Engines

Engine Starting

NOTE: Before starting the engine, read Chapter 3 for detailed information on how to read the instruments and operate the controls.

Whenever you start an engine, watch for any signs of engine problems. If the engine vibrates, misfires, or makes unusual noises, turn the engine off as soon as possible and determine the cause of the problem. Frequently, engine damage may be avoided by a quick response to early indications of problems.

When starting a vehicle equipped with a manual transmission and clutch lockout switch, the clutch pedal must be fully depressed during the entire start sequence. Failure to do so can cause the pinion to release and re-engage, which could cause ring gear and starter pinion damage.

If a vehicle does not start on the first attempt, make sure that the engine has completely stopped rotating before reapplying the starter switch. Failure to do so can cause the pinion to release and re-engage, which could cause ring gear and starter pinion damage.

Moving a vehicle with the starter and/or using the starter to bump the engine for maintenance procedures is strictly prohibited. Use of these methods to bump the engine over or move the vehicle can cause the pinion to release and re-engage, which could cause ring gear and starter pinion damage.

IMPORTANT: Ring gear and starter pinion damage caused by improper starting procedures is not warrantable.

Pre-Start

NOTE: These pre-start steps apply to all engines.

1.

Perform the engine pretrip inspection and daily maintenance checks in Chapter 9 .

2.

Set the parking brake.

3.

For manual transmissions, place the transmission in neutral and disengage the clutch.

3.

For automatic transmissions, make sure the transmission shift control is in neutral or park.

NOTE: On vehicles equipped with a neutral start switch, the transmission must be in neutral before the engine can be started. For air start systems, check the air supply before starting the engine. There must be 100 psi (689 kPa) of air pressure available.

Starting Precautions, All Engines

Do not use any starting aid, such as ether, in engines with an intake air preheater. This could cause an explosion, resulting in serious personal injury or death.

NOTE: Some starters are equipped with optional overcrank protection. If overcranking occurs, a thermostat breaks the electrical circuit to the starter motor until the motor has cooled.

Protect the turbocharger during the start-up by not opening the throttle or accelerating the engine above 1000 rpm until minimum engine idle oil pressure registers on the gauge. Failure to do so could damage the turbocharger.

Mercedes-Benz

NOTE: Before doing these steps, do the steps in "Pre-Start."

Never attempt to start any Mercedes-Benz electronic engine using ether or any other starting fluid. Serious engine damage could result.

1.

Turn the ignition switch to the on position ( Fig. 4.1 ). All the electronic gauges on the ICU (instrumentation control unit) complete a full sweep of their dials, the warning and indicator lights light up, and the buzzer sounds for three seconds.

Fig. 4.1, Ignition Switch Positions

IMPORTANT: On vehicles equipped with an intake air preheater, the amber INTAKE HEATER indicator stays on for a minimum of two seconds, regardless of coolant temperature. Wait until the INTAKE HEATER indicator goes out before attempting to start the engine.

2.

Turn the ignition switch to the start position. Without touching the throttle pedal, start the engine.

3.

Idle the engine for one to three minutes at 700 rpm (600 rpm for 6-cylinder engines) before operating the engine under load.

4.

Check the oil pressure gauge for any drop in lubricating oil pressure or mechanical malfunction in the lubricating oil system. Minimum oil pressure at idle is 7 psi (50 kPa).

Do not rev the engine if the oil pressure gauge indicates no oil pressure. Shut down the engine if no oil pressure appears within approximately ten seconds. Check to determine the cause of the problem. Operating the engine with no oil pressure will damage the engine.

Caterpillar

NOTE: Before doing these steps, do the steps in "Pre-Start."

1.

Turn the ignition switch to the on position ( Fig. 4.1 ). The amber CHECK ENGINE indicator comes on for five seconds.

IMPORTANT: On vehicles equipped with an intake air preheater, the amber INTAKE HEATER indicator stays on for a minimum of two seconds, regardless of coolant temperature. Wait until the INTAKE HEATER indicator goes out before attempting to start the engine.

2.

Turn the ignition switch to the start position. Release the switch the moment the engine starts.

2.1

If the engine does not start after 15 to 20 seconds of cranking, turn the ignition switch off.

2.2

Wait two minutes to allow the starter motor to cool. Turn the ignition switch back to the on position and try to start the engine again.

2.3

As soon as the engine starts, release the ignition switch allowing the engine to run at a slow idle.

If the oil pressure is too low, shut down the engine immediately to prevent serious damage. If the vehicle is equipped with an automatic shutdown system, the engine will shut down after 30 seconds.

3.

The engine may be operated at low load and speed once the engine oil pressure has reached 10 psi (69 kPa) and air pressure (if applicable) has reached 64 to 76 psi (441 to 524 kPa).

4.

When the engine has reached the minimum operating temperature of 160°F (71°C), the engine may be operated at full load.

Cummins

Never attempt to start any Cummins IS series electronic engine (ISB, ISC, ISL) using ether or any other starting fluid. Serious engine damage could result.

NOTE: Before doing these steps, do the steps in "Pre-Start."

1.

Turn the ignition switch to the on position ( Fig. 4.1 ). The amber CHECK ENGINE indicator comes on for five seconds. Leave the ignition switch on until the CHECK ENGINE indicator goes out.

IMPORTANT: On vehicles equipped with an intake air preheater, the amber INTAKE HEATER indicator stays on for a minimum of two seconds, regardless of coolant temperature. Wait until the INTAKE HEATER indicator goes out before attempting to start the engine.

2.

Turn the ignition switch to the start position. After the engine starts, release the key.

3.

Bring the engine up to operating speed gradually as it warms up and develops stable oil pressure.

NOTE: When the engine is started, it takes a short time to build up a lubricating oil film between the shafts and bearings, and between the pistons and liners. The oil pressure gauge indicates any drop in lubricating oil pressure within 15 seconds of engine start-up.

4.

If minimum engine oil pressure at idle of 10 psi (69 kPa) does not register within 15 seconds, shut down the engine.

Protect the turbocharger during the start-up by not opening the throttle or accelerating the engine above 1000 rpm until minimum engine idle oil pressure registers on the gauge. Failure to do so could damage the turbocharger.

5.

Idle the engine for three to five minutes at 1000 rpm before operating the engine under load.

Detroit Diesel

NOTE: Before doing these steps, do the steps in "Pre-Start."

1.

Turn the ignition switch to the on position ( Fig. 4.1 ). The CHECK ENGINE and ENGINE PROTECT indicators should come on and go out within six to ten seconds.

IMPORTANT: On vehicles equipped with an intake air preheater, the amber INTAKE HEATER indicator stays on for a minimum of two seconds, regardless of coolant temperature. Wait until the INTAKE HEATER indicator goes out before attempting to start the engine.

2.

When all the indicators go out, turn the ignition switch to the start position. If the engine won't start within 15 seconds, release the ignition switch and allow the starter motor to cool.

IMPORTANT: If the engine won't start, check the main engine power fuses. The fuses are located along the main engine electrical harness on the left frame rail, near the batteries. If the fuses are blown, replace the fuses. Be sure to find the cause of the blown fuses as soon as possible.

Never pour fuel or other flammable liquid into the air inlet opening in the air intake in an attempt to start the vehicle. This could result in a flash fire causing serious personal injury or property damage.

3.

Check the oil pressure gauge immediately after starting the engine.

4.

If no pressure registers within 10 to 15 seconds or the ENGINE PROTECT indicator comes on, shut down the engine and check the lubricating oil system.

Protect the turbocharger during the start-up by not opening the throttle or accelerating the engine above 1000 rpm until minimum engine idle oil pressure of 12 psi (83 kPa) registers on the gauge.

5.

Idle the engine for about five minutes at 1000 rpm before operating the engine under load.

Cold Weather Starting

Do not use any starting aid, such as ether, in engines with an intake air preheater. This could cause an explosion, resulting in serious personal injury or death.

Modern electronic engines do not normally require special starting aids. At low temperatures, intake air preheaters, manifold preheaters, or water jacket heaters are sometimes used to assist in starting.

Mercedes-Benz

The intake air preheater is activated by turning the ignition switch to the on position ( Fig. 4.1 ). If the engine is at normal temperature, the amber INTAKE HEATER indicator goes out after two seconds.

If the temperature is low enough to require the heater, the amber INTAKE HEATER indicator stays on while the intake air preheater warms up. After the indicator goes out, start the engine. If the engine doesn't start after about 30 seconds of cranking, turn the key to the off position and wait two minutes; then repeat the starting procedure.

NOTE: If the engine doesn't start on the second try, wait at least five minutes before using the intake air preheater again.

Caterpillar

Caterpillar truck engines with direct injection are designed to start at temperatures above 32°F (0°C) without using start systems. If the temperature is below 32°F (0°C), startability will be improved by the use of an automatic ether injection system and/or a jacket water heater.

Directing ether at the heater element in the intake air preheater could cause extensive engine damage.

The intake air preheater is activated by turning the ignition switch to the on position ( Fig. 4.1 ). If the engine is at normal temperature, the amber INTAKE HEATER indicator goes out after two seconds.

If the temperature is low enough to require the heater, the INTAKE HEATER indicator stays on while the intake air preheater warms up. After the indicator goes out, start the engine.

IMPORTANT: Attempting to start the engine before the INTAKE HEATER indicator has gone off could result in excessive white smoke at startup.

If the engine doesn't start after 15 to 20 seconds of cranking, turn the key to the off position and wait two minutes; then repeat the starting procedure.

Cummins

The cold start system approved for use on Cummins engines has been based upon starting aid capabilities to –25°F (–32°C).

Turn the ignition switch to the on position ( Fig. 4.1 ). If the engine is at normal temperature, the amber INTAKE HEATER indicator goes out after two seconds.

If the temperature is low enough to require the heater, the INTAKE HEATER indicator stays on while the intake air preheater warms up. After the indicator goes out, start the engine.

Run the engine slightly above idle until oil pressure shows on the gauge. If oil pressure doesn't show on the gauge within 30 seconds of starting, turn the key to the off position and wait one minute; then repeat the starting procedure.

Starting After Extended Shutdown or Oil Change

Do the following steps after an oil change or after the engine has been shut down for more than three days:

1.

Disconnect the electrical connector from the fuel pump solenoid valve.

2.

Crank the engine until oil pressure shows on the gauge.

3.

Connect the electrical connector to the fuel pump solenoid valve.

4.

Start the engine. After one minute, shut down the engine and check for leaks.

5.

Allow five minutes for the oil to settle, then check the engine oil level and add oil if needed. Do not overfill.

Engine Break-In

Mercedes-Benz

Every Mercedes-Benz engine is tested on a dynamometer before shipment. Therefore, no break-in period is necessary for the MBE900 engine. Before running the engine for the first time, follow the instructions in Chapter 2 of the MBE900 Engine Operator's Manual .

Caterpillar

Every Caterpillar engine must pass a full-load operation test on a dynamometer before shipment, eliminating the need for a break-in period. Only an initial operational check is necessary.

Cummins

Cummins electronic engines are run on a dynamometer before being shipped from the factory. They do not require a break-in period.

NOTE: Special break-in oils are not recommended for new or rebuilt Cummins engines.

Detroit Diesel

Detroit Diesel engines can be put to work upon delivery without having to follow a formal break-in schedule. The engine has been "run-in" on a factory dynamometer during performance and quality assurance tests prior to shipment.

Engine Operation

General Information

Operating vehicles with diesel engines in areas where there are concentrated flammable vapors (such as diesel, gasoline, or propane fumes) can create a hazardous situation. These vapors can be drawn into the engine through the air intake, and cause engine overspeed. Be especially cautious of low-lying or closed-in areas, and always check for signs that flammable vapors may be present.

Do not operate the engine in an area where flammable vapors such as gasoline or diesel fumes are present. Shut down the engine when in an area where flammable liquids or gases are being handled. Failure to observe these precautions could result in serious injury or death.

All diesel engines have been built to comply with the requirements of the Federal (U.S.) Clean Air Act. Once an engine is placed in service, the responsibility for meeting both state and local regulations is with the owner/operator. Good operating practices, regular maintenance, and correct adjustments are factors which will help to stay within the regulations.

Adequate maintenance of the engine, which is the responsibility of the owner/operator, is essential to keep the emission levels low.

The driver should be familiar with the vehicle warning system in order to bring the vehicle to a safe stop if the engine malfunctions. If the driver doesn't understand how the warning system works, an engine shutdown could occur causing a safety hazard. See Chapter 3 for information on the control panels for the various engines.

Mercedes-Benz

While you are driving, watch for any signs of engine problems. If the engine overheats, uses excessive fuel or lubricating oil, vibrates, misfires, makes unusual noises, or shows an unusual loss of power, turn the engine off as soon as possible and determine the cause of the problem. Frequently, engine damage may be avoided by a quick response to early indications of problems.

1.

Use the tachometer to determine when to shift. Follow the pattern on the shift lever when moving through the gears.

2.

Depending on the vehicle gearing, the posted speed limit can sometimes allow operation in either of the top two gears; however, for improved operating efficiency (fuel economy and engine life), operate in the top gear at reduced rpm, rather than in the next lower gear at the maximum rpm.

3.

Cruise at partial throttle whenever road conditions and speed requirements permit. This driving technique permits operating within the most economical power range of the engine.

4.

Use lower gears in steep downhill driving. Normally, the gear used to descend a hill is the same gear used to climb a hill of the same grade.

5.

Never allow the engine to exceed the rated speed. Use the exhaust brake and the optional constant-throttle brake, if installed, to lower engine rpm below the rated speed.

6.

Never allow the engine to idle for more than 30 minutes. Excessive idling can cause oil to leak from the turbocharger.

Stop the engine at the first sign of malfunction. Almost all malfunctions give some warning to the operator before significant damage occurs. Many engines are saved because alert operators heed the warning signs (sudden drop in oil pressure, unusual noises, etc.) and immediately shut down the engine.

NOTE: Long periods of idling are not good for an engine because the combustion chamber temperatures drop so low that the fuel may not burn completely. This will cause carbon to clog the injector spray holes and piston rings, and may result in stuck valves.

If the engine coolant temperature becomes too low, raw fuel will wash the lubricating oil off the cylinder walls and dilute the crankcase oil, causing all moving parts of the engine to suffer from poor lubrication.

Caterpillar

Proper operation and maintenance are key factors in obtaining the maximum life and economy of a vehicle engine. Follow the directions in the Caterpillar Operation and Maintenance Manual and this manual for trouble-free, economical engine operation.

Caterpillar electronic engines can be equipped with a variety of options designed to warn the driver of engine malfunctions. The driver of a vehicle equipped with these engines should know the extent of the warning system in order to bring the vehicle to a safe stop if the engine malfunctions. If the driver doesn't understand how the warning system works, an engine shutdown could cause a safety hazard.

The electronic control system can monitor engine oil pressure, coolant temperature, intake manifold air temperature, and coolant level. There are four customer programmable levels for Caterpillar engine monitoring: off, warning (factory default), derate, and shutdown.

In the engine monitoring off mode the ECM will ignore the oil pressure sensor and coolant level sensor (if installed). Engine monitoring warning mode uses oil pressure, coolant temperature, intake manifold temperature, and the coolant level sensor (if installed and enabled). The CHECK ENGINE indicator will flash and the warning light will come on when the diagnostic code is active. Engine monitoring derate and shutdown modes allow the ECM to alter engine performance or stop the engine to help the engine avoid damage and return to normal conditions.

1.

Operate the engine at low load. After minimum oil pressure is reached and the temperature gauge needle begins to move, the engine may be operated at full load.

1.

Caterpillar electronic engines automatically idle at 900 to 1000 rpm for the correct warm-up time after a cold engine start of less than 40°F (5°C). These electronic engine systems will reduce the idle speed to 600 rpm when the engine has warmed sufficiently to operate the vehicle.

IMPORTANT: Fuel heaters used on vehicles with Caterpillar electronic engines could cause excessive fuel temperatures that affect engine performance and operation of the electronic engine controls. If a fuel heater is used, make sure it has thermostatic controls. If the fuel heater has a timer, set the timer to activate only for a limited period of time before the engine starts. Make sure the fuel heater is used only for starting the engine.

2.

Select a gear that allows a smooth, easy start without increasing engine speed above low idle or slipping the clutch. Engage the clutch smoothly. Jerky starts waste fuel and put stress on the drivetrain.

2.

It is not necessary to accelerate Caterpillar electronic engines to governed speed in the lower gears to get the vehicle moving, except in a high power demand situation such as starting on a grade.

3.

Continue to upshift until cruising speed is reached. Use only the rpm needed to make an upshift into the next gear. The engine speed needed to make an upshift increases as the truck speed increases. If the truck can be operated in a higher gear after reaching the desired speed, select the highest gear available that will pull the load. Experience with your truck will show you what rpm is needed to make upshifts under various conditions. This progressive shifting technique will lower fuel costs because the engine will be operating at the lowest rpm needed to pull the load.

3.

Caterpillar electronic engines can be programmed to limit engine rpm while the truck is operated in the lower and higher gears. This feature assists the driver in following progressive shifting techniques.

4.

On uphill grades, begin downshifting when the engine rpm falls to 1200 rpm. Fuel economy will be best if you let the engine lug back to around this speed before you downshift. Downshift until a gear is reached in which the engine will pull the load. Let the engine lug down if you can make it to the top of a hill without downshifting.

IMPORTANT: Do not allow Caterpillar electronic engines to exceed 2300 rpm (2100 rpm if equipped with an exhaust brake).

5.

On a downhill grade, do not coast or put the transmission in neutral. Select the correct gear that does not allow the engine to exceed its maximum speed. Use the brakes to limit the truck speed.

5.

A simple rule to follow is to select the same gear (or one gear lower) that would be needed to go up the grade.

6.

As with any engine, prolonged idling of Caterpillar engines is not recommended. An idling engine wastes fuel and if left unattended, is also unsafe.

6.

Caterpillar engines can be programmed to shut off automatically after a specified idling time. The vehicle transmission must be in neutral and the parking brake must be set for the automatic shutoff option to work.

Cummins

Follow the directions in the Cummins Operation and Maintenance Manual and in this manual for trouble-free, economical vehicle engine operation.

1.

Cummins diesel engines produce high horsepower and peak torque characteristics at low rpm. Because of this, it is not necessary to keep the engine "wound up" to deliver the required horsepower at the wheels. These characteristics may also result in less shifting and make shifting at lower rpm (to peak torque) more practical.

2.

Depending on the vehicle gearing, the posted speed limit can sometimes allow operation in either of the top two gears; however, for improved operating efficiency (fuel economy and engine life), operate in the top gear at reduced rpm rather than in the next lower gear at the maximum rpm.

3.

Cruise at partial throttle whenever road conditions and speed requirements permit. This driving technique permits operating within the most economical power range of the engine.

4.

When approaching a hill, open the throttle smoothly to start the upgrade at full power, then shift down as desired to maintain the optimum vehicle speed. The high torque of Cummins engines may permit topping some grades without shifting.

5.

Cummins engines are designed to operate over a wide speed range. More frequent shifting than necessary does not allow proper utilization of this flexibility. The driver who stays in top gear and uses the wider speed range will achieve the best fuel economy.

6.

The Cummins diesel engine is effective as a brake on downhill grades, but care must be used not to overspeed the engine going downhill. The governor has no control over engine speed when the engine is being pushed by the loaded vehicle.

6.

Never turn off the ignition switch while going downhill. With the engine still in gear, fuel pressure will build up against the shutdown valve and may prevent it from opening when the ignition key is turned on.

Do not allow the engine to exceed its governed speed, or serious engine damage could result.

7.

Use a combination of brakes and gears to keep the vehicle under control at all times and to keep the engine speed below the rated governed rpm.

Detroit Diesel

Individual driving habits can make a difference in the performance and economy of any engine. The recommendations below call attention to the techniques that can be employed to save fuel and extend the operating efficiency and life of a new Detroit Diesel engine for the longest possible time.

Engines with Detroit Diesel Electronic Control (DDEC) can be equipped with a variety of options designed to warn the operator of engine problems. The operator of a DDEC-equipped engine should know the extent of the warning system in order to bring the vehicle to a safe stop if the engine malfunctions. If the operator doesn't understand how the system works, an engine shutdown could cause a safety hazard.

All engines have an operating range in which the engine performs most efficiently. The operating range extends from maximum torque rpm at the low end to engine rated speed at the high end. Detroit Diesel engines deliver best fuel economy when operated in the low- and mid-speed segments of the efficiency range and produce maximum horsepower at rated speed, which is also the recommended maximum speed of the engine.

1.

It is seldom necessary to accelerate the engine to governed speed in the lower gears to get the vehicle moving, except in a high power demand situation such as starting on a grade.

1.

To conserve fuel, start off in low gear and develop only the engine speed needed to get rolling. Then, increase engine speed gradually as upward gear shifting progresses.

1.

As described by Detroit Diesel, this progressive shifting technique will get the vehicle up to the desired cruising speed while minimizing noise emission and maximizing fuel economy. A progressive shift pattern is illustrated in Fig. 4.2 .

1. Governed RPM
2. Engine RPM
3. Idle RPM
4. Miles (Kilometers) Per Hour

Fig. 4.2, Progressive Shift Pattern

NOTE: A momentary hesitation in throttle response will occur when a vehicle with a turbocharged engine is started on a grade. Do not disengage the clutch. The rpm will recover and the vehicle will accelerate up the grade.

2.

For city driving, run in the highest gear possible and reduce engine speed. This enables you to operate at a safe speed for traffic conditions while using less fuel and reducing noise. Also, when slowing down for reduced speed zones, remain in your running gear and reduce engine rpm to stay within the speed limit. Avoid downshifting until you are ready to return to highway cruising speed.

3.

For highway cruising and for best fuel economy, run the engine at 80 to 90 percent of rated rpm to maintain highway speed. Engines with 1800 rpm ratings are exceptions and will provide fuel economy when run at their rated speed. Proper gear selection should permit cruising in the economy range with no appreciable sacrifice in desired highway speed.

3.

It is okay to operate below rated rpm at full throttle if you are satisfied with the way the vehicle performs. However, there are times when hilly terrain, high winds, or other conditions make it impractical to operate without reserve power. Such conditions are better met if the vehicle is operated in a lower gear with reserve power available for changes in terrain, wind, etc.

4.

The proper use of gears will shorten time on hills and minimize the amount of shifting. When starting up a hill, gradually depress the accelerator pedal all the way down and keep it there as the vehicle moves up the grade. If the engine continues to maintain a satisfactory road speed, remain in that gear for the entire grade.

4.

If the hill causes a steady decline in engine rpm, downshift as required until the engine can maintain a stable uphill speed. Make full use of each gear before going to a lower gear. By remaining in a gear until arriving at the speed of the next lower gear, the vehicle will top the grade in the best possible time on less fuel and fewer shifts.

5.

Because of their constant horsepower over a wide speed range, Detroit Diesel engines can be operated at full throttle at lower rpm than other engines. This offers benefits in fuel economy and engine life. And more than likely, it will be possible to top most grades without downshifting.

5.

When the vehicle starts into a grade, allow the engine to lug down to maximum torque rpm before downshifting. Downshift, if required, at maximum torque rpm also or at the predetermined road speed for the next lower gear.

5.

Do not be afraid to lug the engine down. It has more than enough torque at low rpm to keep a loaded vehicle moving against a grade and it won't harm the engine.

6.

The driver who is not familiar with the vehicle's shift points can greatly improve driving skill by learning them for all gears. By knowing rather than guessing where the shift points are, it is possible to avoid overspeeding the engine by downshifting too soon or missing the full use of a gear by downshifting too late. The shift points of any vehicle can be determined by a simple road-test method. Run the vehicle and determine the maximum road speed possible in every gear at the engine governed full-load speed setting.

6.

The top road speed possible in a gear would be the shift point for that gear. The results should be recorded in the proper order of shifting and displayed inside the cab.

7.

To slow the vehicle on downgrades and curves (using the engine), shift to a lower gear and allow the vehicle to decelerate in that gear. The engine provides maximum braking effect when running at the top end of the operating range, but it must not be allowed to exceed its full-load rated rpm. Continue to downshift as further reduction in vehicle speed is required. If the vehicle is above the allowable maximum speed of a lower gear, use the service brakes to slow the vehicle to an acceptable speed where the transmission may be downshifted safely. Again, the importance of knowing the shift points is demonstrated.

Do not allow the engine to exceed its governed speed, or serious engine damage could result.

IMPORTANT: The engine governor has no control over engine rpm when the engine is being pushed by a loaded vehicle down a grade. Use service brakes and gears in combination on long grades to keep the vehicle speed under control and the engine rpm below full-load rated governed speed.

NOTE: Essential information regarding the operation and care of Allison automatic transmissions is contained in the Allison Driver's Handbook. Applying the knowledge presented will not only make driving easier, but will give the maximum benefits from an Allison-equipped vehicle.

Maintenance literature is also available for drivers of Allison-equipped vehicles who desire trouble-free performance and maximum life from their equipment. These maintenance books are available from any authorized Detroit Diesel engine distributor.

8.

As with all engines, prolonged idling of Detroit Diesel engines is not recommended. An idling engine wastes fuel and if left unattended, is also unsafe.

8.

A Detroit Diesel Electronic Control (DDEC) engine can be equipped to shut off automatically after a specified idling time. The vehicle transmission must be in neutral and the parking brake must be set for the automatic shutoff option to work. To start the engine, follow the normal start-up procedure.

8.

Engines equipped with DDEC will idle fast when cold. As the engine warms up to operating temperature, the idle speed will decrease. Warm the engine until idle speed is normal before operating the vehicle.

Cruise Control

The cruise control is activated by the CRUISE ON and SET/RESUME switches located on the instrument control panel ( Fig. 4.3 ) or by optional PAUSE, RESUME, and SET buttons on the transmission shift knob ( Fig. 4.4 ). The minimum speed at which cruise control can be used on Mercedes-Benz, Caterpillar, and Cummins electronic engines is 30 mph (48 km/h). On Detroit Diesel engines, the minimum speed at which cruise control can be used is 35 mph (56 km/h).

1. Cruise Control CRUISE ON Switch
2. Cruise Control SET/RESUME Switch
3. Engine Shutdown Override/Check Switch

Fig. 4.3, Cruise Control Switches and Engine Shutdown Override/Check Switch

Fig. 4.4, Cruise Control, Transmission Shift Knob Buttons

NOTE: On Caterpillar engines, the minimum and maximum speed cruise control set limits can be programmed by authorized personnel into the ECM personality module.

Do not use the cruise control system when driving conditions do not permit maintaining a constant speed, such as in heavy traffic or on roads that are winding, icy, snow-covered, slippery, or roads with a loose driving surface. Failure to follow this precaution could cause a collision or loss of vehicle control, possibly resulting in personal injury or property damage.

Do not attempt to shift gears without using the clutch pedal when the cruise control is engaged. Failure to follow this precaution will result in a temporarily uncontrolled increase in engine speed; transmission damage and gear stripping could result.

1.

To cruise at a particular speed:

1.1

Move the CRUISE ON switch on the instrument panel to on.

1.2

Hold the throttle down until the speedometer indicates the desired speed.

1.3

Momentarily move the SET/RESUME switch on the instrument control panel to SET or push the SET button on the transmission shift knob.

2.

To disengage the cruise control:

2.1

Depress the brake pedal, or clutch pedal, or

2.2

Move the CRUISE ON switch on the instrument control panel to off or push the PAUSE button on the transmission shift knob.

3.

To resume a preselected cruise speed:

3.1

If the CRUISE ON switch on the instrument control panel is in the off position, move it to on.

3.2

Momentarily move the SET/RESUME switch on the instrument control panel to RESUME or push the RESUME button on the transmission shift knob. Cruise will return to the last speed selected.

To adjust cruise speed up or down, hold the SET/RESUME switch on the instrument control panel at RESUME to accelerate or at SET to decelerate, or press the RESUME (accelerate) or SET (decelerate) button on the transmission shift knob, until the desired speed is attained.

NOTE: The resume vehicle speed memory is not maintained if the ignition is shut off. Also, it is not maintained with Cummins engines if the CRUISE ON switch is turned to off and with Detroit Diesel engines if the CRUISE ON switch is turned to off for more than 10 seconds.

Power Takeoff (PTO) Governor

General Information

All electronic engines may be equipped with a PTO governor. This mode is used only when the vehicle is parked. The PTO mode is activated by the CRUISE ON and SET/RESUME switches on the dash ( Fig. 4.3 ) or by optional PAUSE, RESUME, and SET buttons on the transmission shift knob ( Fig. 4.4 ).

1.

To engage the PTO:

1.1

Move the CRUISE ON switch on the instrument control panel to on.

1.2

Hold the throttle pedal down until the desired engine speed is indicated on the tachometer.

1.3

Momentarily move the SET/RESUME switch on the instrument control panel to SET or push the SET button on the transmission shift knob.

IMPORTANT: Two PTO engine speeds can be preset on Cummins CELECT Plus engines. With the CRUISE ON switch in the on position, move the SET/RESUME switch to SET to reach the first preset value or, move the switch to RESUME for the second preset value. After one preset value has been selected, turn the CRUISE ON switch to off, then turn it back to on before using the second preset value.

2.

To disengage the PTO:

2.1

Depress the brake pedal or clutch pedal, or, (only on Cummins CELECT Plus engines the throttle pedal), or

2.2

Move the CRUISE ON switch on the instrument control panel to off or press the PAUSE button on the shift knob.

3.

To resume a previously selected engine speed:

3.1

If the CRUISE ON switch on the instrument control panel is in the off position, move it to on.

3.2

Momentarily move the SET/RESUME switch on the instrument control panel to RESUME or press the RESUME button on the transmission shift knob.

3.2

To adjust engine speed up or down, hold the SET/RESUME switch on the instrument control panel at RESUME to accelerate or at SET to decelerate until the desired speed is reached, or press the RESUME button on the transmission shift knob to accelerate or the SET button to decelerate until the desired speed is reached.

NOTE: The resume engine speed memory is not maintained if the ignition is shut off or, on Cummins engines, if the CRUISE ON switch is turned to off.

Detroit Diesel

Some Detroit Diesel engine vehicles have separate controls for the PTO. If equipped with a preset nonadjustable PTO engine speed, there is only an on/off switch labeled FAST IDLE. If the vehicle is equipped with a variable PTO engine speed, there are two controls: an on/off switch, and a potentiometer knob. Both of these are labeled GOVERNOR.

To operate the PTO with separate PTO controls:

1.

Apply the parking brakes.

2.

Turn on the switch labeled GOVERNOR (or FAST IDLE for vehicles with a preset PTO system).

3.

For vehicles with a variable PTO, use the potentiometer knob to adjust the engine rpm.

Cold Weather Operation

General Information

Satisfactory performance of a diesel engine operating in low ambient temperatures requires modification of the engine, surrounding equipment, operating practices, and maintenance procedures. The lower the temperatures the greater the amount of modification required, and yet with the modifications applied, the engines must still be capable of operation in warmer climates without extensive changes.

The following information is provided to engine owners, operators, and maintenance personnel on how the modifications can be applied to get satisfactory performance from their diesel engines.

There are three basic objectives:

Reasonable starting characteristics followed by practical and dependable warm-up of the engine and equipment.

A unit or installation which is as independent as possible from external influences.

Modifications which maintain satisfactory operating temperatures with a minimum increase in maintenance of the equipment and accessories.

If satisfactory engine temperature is not maintained, higher maintenance cost will result due to increased engine wear.

Special provisions to overcome low temperatures are definitely necessary, whereas a change to a warmer climate normally requires only a minimum of revision. Most of the accessories should be designed in such a way that they can be disconnected so there is little effect on the engine when they are not in use.

IMPORTANT: If a winterfront is used on a vehicle with an electronic engine equipped with a charge air cooler, make sure that there are slit openings distributed across the face of the winterfront to allow airflow through the entire charge-air-cooler core. Do not use a winterfront with closed areas that block uniform air flow across all sections of the charge-air-cooler crossflow tubes. This will adversely affect the operation and durability of the charge air cooler.

Mercedes-Benz

Special precautions must be taken during cold weather. For service products to use in cold weather, see Chapter 5 of the MBE900 Engine Operator's Manual .

IMPORTANT: At outside temperatures below –4°F(–20°C), a coolant preheater is recommended.

1.

Check for cracks in the battery cases, for corrosion of the terminals, and for tightness of the cable clamps at the terminals. Run a load test to determine full or partial charging. Charge the batteries to full capacity. Replace any battery that is unable to hold full charge or is physically damaged.

2.

Check the alternator output. Check the condition and tension of the poly-V belt.

3.

Periodically check the coolant mixing ratio (concentration of antifreeze in the coolant). Add more if necessary. The coolant mixing ratio should never rise above 55 percent antifreeze.

4.

Use low-viscosity lubricating oils for adequate lubrication.

5.

At temperatures below 32°F (0°C), do not use summer-grade (2-D) diesel fuel. To avoid fuel problems due to paraffin separation, use winter-grade (1-D or winterized 2-D) diesel fuel only.

The addition of kerosene lowers the flash point of diesel fuel. To prevent fire and risk of injuries due to burning, do not smoke or use open flames around fuel mixed with kerosene. Comply with all appropriate safety regulations.

6.

When winter-grade diesel fuel is not adequate, it is possible to mix kerosene with the diesel fuel. Add the kerosene only when refilling the tank, and before adding the diesel fuel.

NOTE: Engine power may drop according to the proportion of kerosene. For this reason, never add more than 50 percent kerosene to the fuel.

Caterpillar

If the engine is in good mechanical condition and the precautions necessary for cold weather operation are taken, ordinary cold weather will not cause difficulty in starting or loss of efficiency.

If the engine does not start, prime the fuel system.

For cold weather operation, use the following guidelines:

1.

When starting the engine in temperatures below 32°F (0°C), use engine lubricants of lower viscosity. See the engine operation and maintenance manual for specifications.

2.

When operating in temperatures below 32°F (0°C), use sufficient antifreeze solution in the cooling system to prevent freezing.

3.

During cold weather, give more attention to the condition of the batteries. Test them frequently to ensure sufficient power for starting. Inspect all switches and connections in the electrical system and keep them in good condition to prevent losses through poor contacts. See Group 15 in the Business Class® Trucks Service Manual for detailed information.

4.

If so equipped, turn off the battery disconnect switch after the engine is stopped to prevent battery discharge while the starter motor is cooling.

4.

For starting below 0°F (–18°C), an optional cold-weather starting assist is recommended. For temperatures below –10°F (–23°C), consult your Caterpillar dealer for recommendations.

Do not use any starting aid, such as ether, in engines with an intake air preheater. This could cause an explosion, resulting in serious personal injury or death.

5.

Customer parameters may include cold mode operation. When the coolant temperature is below 64°F (18°C), the system puts the engine in cold mode, limiting engine power, advancing timing, and adjusting the low idle to 600 rpm to improve warm-up time. The system will keep the engine in cold mode until coolant temperature rises above 64°F (18°C) or until the engine has been running for 12 minutes. The system will then stop the cold mode and allow the engine to operate normally.

6.

Fuel cloud point is the temperature at which wax crystals become visible, which is generally above the pour point of the fuel. To keep the fuel filter elements from plugging with wax crystals, the cloud point should be no higher than the lowest ambient temperature at which the engine must start.

Cummins

The two most commonly used terms associated with preparation of equipment for low-temperature operation are "winterization" and "arctic specifications."

Winterization of the engine and/or components so that starting and operating are possible in the lowest temperature to be encountered, requires:

Proper lubrication with low-temperature lubricating oils.

Protection from the low-temperature air. The metal temperature does not change, but the rate of heat dissipation is affected.

Fuel of the proper grade for the lowest temperature.

Heat to raise the engine block and component temperatures to at least –25°F (–32°C) for starting in lower temperatures.

Electrical equipment capable of operating in the lowest expected temperature. All switches, connections, and batteries in the electrical system should be inspected and kept in good condition to prevent losses through poor contacts.

Arctic specifications refer to the design of material and specifications of components necessary for satisfactory engine operation in extremely low temperatures to –64°F (–53°C). Contact the nearest Freightliner dealer or Cummins engine dealer, to obtain the special items required.

"Antileak" antifreezes are not recommended for use in Cummins engines. Although these antifreezes are chemically compatible with DCA water treatment, the "antileak" agents may clog the coolant filters.

IMPORTANT: Fuel heaters used on vehicles with Cummins CELECT engine systems could cause high fuel temperatures that affect engine performance and operation of the electronic engine controls. If a fuel heater is used, make sure it has thermostatic controls. If the fuel heater has a timer, set the timer to activate only for a limited period of time before the engine starts. Make sure the fuel heater is used only for starting the engine.

Detroit Diesel

Preparations made in advance of winter and maintenance performed during the cold months will help to ensure efficient engine starting and operation.

1.

Engine oil thickens as it gets colder, slowing cranking speed. When cold, multigrade oil offers less resistance to the cranking effort of the engine and permits sufficient rpm to be developed to start the engine. See "Lubricating Oil Recommendations" in the Detroit Diesel Owner's and Operator's Guide for specific recommendations.

2.

When an engine equipped with a DDEC system is started at temperatures below 25°F (–4°C), the idle speed automatically increases to 900 rpm. The injection timing is also advanced to decrease white smoke. As the engine oil warms up, the idle speed gradually decreases. When the oil temperature reaches 122°F (50°C), both the idle speed and the injection timing return to normal.

3.

During cold weather, the batteries should be tested more frequently to ensure ample power for starting. All electrical connections should be tight and in good condition to prevent losses through loose or corroded connections.

4.

The ether start system should be properly charged and in good working order.

5.

Ethylene glycol base antifreeze is recommended. An inhibitor system is included in this type of antifreeze, and the corrosion protection is sufficient as long as the recommended concentration range of 30 to 67 percent (antifreeze to water by volume) is employed.

6.

If the engine is to be operated in arctic temperatures, consult the nearest Freightliner dealer or an authorized Detroit Diesel engine dealer for information regarding availability of special cold-weather equipment.

High Altitude Operation

Engines lose horsepower when operated at high altitude because the air is too thin to burn as much fuel as at sea level. This loss is about three percent for each 1000 feet (300 m) altitude above sea level for a naturally aspirated engine. Most turbocharged engines are rated for higher altitudes than naturally aspirated engines.

An engine will have smoky exhaust at high altitudes unless a lower gear is used. The engine will not demand full fuel from the fuel system unless the engine is altitude-compensated by the use of a turbocharger. Shift gears as needed to avoid excessive exhaust smoke.

Engine Shutdown

Mercedes-Benz

If any of the following occur, shut down the engine immediately.

The oil pressure swings back and forth or falls sharply.

Engine power and rpm fall even though the accelerator pedal remains steady.

The exhaust pipe gives off heavy smoke.

The coolant and/or oil temperature climb abnormally.

Abnormal sounds suddenly occur in the engine or turbocharger.

1.

With the vehicle stopped, apply the parking brakes and place the transmission in neutral.

Idle the engine one to two minutes before shutting it down, if this can be done without damage to the engine. After hard operation, shutting down the engine without idling may cause damage to the turbocharger.

2.

Allow the engine to idle one to two minutes before shutting it down. This allows the lubricating oil and the coolant to carry heat away from the combustion chambers, bearings, shafts, and seals. The extreme heat may cause bearings to seize or oil seals to leak.

IMPORTANT: Bearings and seals in the turbocharger are subjected to the high heat of combustion exhaust gases. While the engine is running, this heat is carried away by oil circulation, but if the engine is stopped suddenly, the turbocharger temperature may rise as much as 115°F (46°C).

Except in emergency, do not shut down the MBE900 engine when the coolant temperature is above 194°F (90°C). To do so could damage the engine.

3.

Turn off the ignition switch and shut down the engine.

Caterpillar

Stopping the engine immediately after it has been working under load can result in overheating and accelerated wear of the engine components. Excessive temperatures in the turbocharger centerhousing will cause oil coking problems. Follow the procedure, outlined below, to allow the engine to cool.

1.

With the vehicle stopped, apply the parking brakes.

2.

Reduce the engine speed to low idle.

3.

Place the transmission shift lever in neutral.

NOTE: If the engine has been operating at low loads, run it at low idle for 30 seconds before stopping. If the engine has been operating at highway speed or at high loads, run it at low idle for three minutes to reduce and stabilize internal engine temperatures before stopping.

4.

Check the crankcase oil level while the engine is stopped. Maintain the oil level between the add and full marks on the dipstick.

5.

Turn off the ignition switch and shut down the engine.

6.

If equipped with an idle shutdown timer, it can be set to shut the engine down after a preset amount of time. Ninety seconds before the preset shutdown time, the CHECK ENGINE indicator will begin to flash at a rapid rate. If the position of the clutch pedal or service brake changes during this final ninety seconds (diagnostic light flashing) the idle shutdown timer will be disabled until reset.

7.

After stopping the engine, fill the fuel tank.

8.

If temperatures below 32°F (0°C) are expected, allow the engine water jacket expansion tank to cool, then check the coolant for proper antifreeze protection. The cooling system must be protected against freezing to the lowest expected outside temperature. Add permanent-type antifreeze if required.

9.

Repair any leaks, perform minor adjustments, tighten loose bolts, etc. Observe the vehicle mileage or the service meter reading, if so equipped. Perform periodic maintenance as instructed in the Lubrication and Maintenance Chart in the Caterpillar Operation and Maintenance Management.

Cummins

1.

With the vehicle stopped, apply the parking brakes and place the transmission in neutral.

2.

Idle the engine three to five minutes before shutting it down. This allows the lubricating oil and the water to carry heat away from the combustion chambers, bearings, shafts, etc. This is especially important with turbocharged engines.

2.

Bearings and seals in the turbocharger are subjected to the high heat of combustion exhaust gases. While the engine is running, this heat is carried away by oil circulation, but if the engine is stopped suddenly, the turbocharger temperature may rise as much 115°F (46°C). The extreme heat may cause bearings to seize or oil seals to leak.

3.

Do not idle the engine for excessively long periods. Long periods of idling are not good for an engine because the combustion chamber temperatures drop so low the fuel may not burn completely. This will cause carbon to clog the injector spray holes and piston rings and may result in stuck valves.

3.

If the engine coolant temperature becomes too low, raw fuel will wash the lubricating oil off the cylinder walls and dilute the crankcase oil; therefore, all moving parts of the engine will suffer from poor lubrication.

4.

Turn off the ignition switch and shut down the engine.

Stop the engine at the first sign of malfunction. Almost all malfunctions give some warning to the operator before significant damage occurs. Many engines are saved because alert operators heed the warning signs (sudden drop in oil pressure, unusual noises, etc.) and immediately shut down the engine.

Detroit Diesel

1.

With the vehicle stopped, apply the parking brakes and place the transmission in neutral.

2.

Allow the engine to run at half speed or slower with no load for four to five minutes to cool the engine gradually and uniformly.

3.

Turn off the ignition switch and shut down the engine.

Engine Braking System, Optional

Constant-Throttle Valves (MBE900 only)

To increase braking performance, the Mercedes-Benz MBE900 engine can be equipped with constant throttles in each combustion chamber. Small valves built into the cylinder head allow a small amount of compressed air to escape through the exhaust port during the combustion stroke. The constant-throttle valves are open during the entire time that the engine brake is activated. Although some braking ability is lost because the valves are constantly open, constant-throttle braking is quieter in operation than other types of engine brakes.

When only the exhaust brake is installed, a two-position switch on the dash controls the engine braking system. The exhaust brake is only active when the engine speed is between 900 and 2,700 rpm. Depressing the accelerator or clutch pedal deactivates the exhaust brake. The ABS system, when active, also deactivates the exhaust brake.

When both the exhaust brake and the constant throttles are installed, a three-position switch on the dash controls the engine braking system. The exhaust brake can be used alone or together with constant-throttle valves for steep or long grades. Like the engine brake, the constant throttles are deactivated when the accelerator or clutch pedal is depressed. The ABS system, when active, also deactivates constant-throttle braking.

Jacobs Engine Brake

A Jacobs engine brake is a hydraulic-electric engine attachment that converts a diesel engine into an air compressor. This is done by changing engine exhaust valve operation. An engine brake is not a substitute for a service braking system, except in emergencies, because it does not provide the precise control available from the service brakes.

The Jake Brake is controlled by a single, dash-mounted paddle switch with three positions: OFF, LO and HI.

Jacobs Engine Brake Operation

To engage the engine brake, the dash switch must be in the LO or HI position and both the clutch and throttle pedals must be fully released. To disengage the engine brake, depress the throttle or clutch pedal, or move the dash switch to OFF.

The engine brake must be disengaged when shifting gears. The clutch must be used if the dash switch is in the LO or HI position. If the engine brake is engaged when the transmission is in neutral, the braking power of the engine brake can stall the engine, which could result in loss of vehicle control, possibly causing personal injury and property damage.

Since the engine brake is most effective at rated engine speed, gear selection is very important. Gearing down the vehicle within the limits of the rated engine speed makes the engine brake more effective. Maximum braking occurs with the use of the lowest gear that does not exceed the rated engine speed. A rule of thumb for gear choice is to select the gear that normally would be used to climb an approaching downhill grade. Generally, this same gear can be used with the engine brake for a controlled descent of the hill.

"Control speed" is the speed at which the engine brake performs 100 percent of the required downhill braking, resulting in a constant speed of descent. The control speed varies depending on vehicle weight and the downhill grade.

For faster descent, select a higher gear than that used for control speed. Service brakes must then be used intermittently to prevent engine overspeed and to maintain desired vehicle speed.

IMPORTANT: When descending a grade, remember that frequent use of service brakes causes them to become hot, which results in a reduction of their stopping ability. Grade descent speed should be such that the service brakes are used infrequently and that they remain cool, thus retaining their effectiveness.

A driver may descend slower than control speed by selecting a lower gear, one that will not overspeed the engine. The engine brake retarding force will then be sufficient to cause vehicle deceleration. Occasional deactivation of the engine brake may be necessary to maintain the designated road speed under these conditions.

The engine brake can be used to stop a vehicle if the service brakes quit working. By energizing the engine brake as soon as a service brake problem is apparent, a retarding effect is applied to the vehicle. As grade conditions permit, the driver can progressively downshift, using the engine brake in each gear. Eventually, the engine brake will stop the vehicle.

Using the engine brake as a primary braking system when the service brakes are operable is dangerous. This can cause long, unpredictable stopping distances, possibly resulting in personal injury or property damage.

Whenever vehicle braking is required, the engine brake may be used with the service brakes. There is no time limit for operation of the engine brake.

1.

After the engine is warmed up and the vehicle is in motion, move the paddle switch to the desired position, LO or HI. Depending on the engine model, LO will provide 1/3 or 1/2 of the full braking capacity of the engine. HI will provide maximum engine braking.

2.

The engine brake activates when the dash switch is in LO or HI position and the driver's feet are removed from both the clutch and throttle pedals. If the engine brake fails to activate, stop the vehicle in a safe spot and check the adjustment of the throttle and clutch switches. If no cause can be detected in the electrical system, check the engine brake system.

3.

To obtain maximum retarding, maintain the top governed speed of the engine through appropriate selection of gears when the engine brake is in use.

4.

When either the clutch or throttle pedal is depressed, the engine brake is deactivated.

If the engine brake fails to shut off when either the throttle or clutch pedal is depressed, place the dash switch in the OFF position and do not use the engine brake until the throttle or clutch switch system is repaired. If the engine brake fails to shut off when the dash switch is turned off, the engine should be shut down and the engine brake repaired before continuing operation. Failure to do so could result in damage to the engine.

Exhaust Braking System, Optional

General Information

An exhaust brake is an optional auxiliary braking system that assists but does not replace the service brake system. The exhaust brake switch located on the control panel, in combination with the accelerator and clutch pedals, allows the driver to make maximum use of the exhaust brake in off-highway and mountain driving as well as in traffic or high speed highway driving.

The exhaust brake is a butterfly type valve mounted in the exhaust pipe. When the driver's foot is not on the accelerator pedal and the exhaust brake switch is in the on position, an air cylinder shuts the butterfly valve which restricts the flow of exhaust gases and retards the engine. This retarding action is carried through the engine and drivetrain, slowing the vehicle and reducing the need for frequent service brake applications.

Exhaust brakes are not intended for use as the primary braking system during vehicle operation.

Starting the Engine

Before starting the engine, make sure that the exhaust brake switch is in the off position. Do not turn the exhaust brake on until the engine has reached normal operating temperatures.

Driving Downhill

While approaching a steep grade, make sure that the exhaust brake switch is in the on position. The exhaust brake comes on as soon as you remove your foot from the accelerator pedal. While going down the grade, use a low enough gear to safely descend with a minimum application of the service brakes. As a general guideline, use the same gear as you would to ascend the hill.

Do not allow the engine to exceed its governed speed, or serious engine damage could result.

Apply the service brakes to reduce the engine rpm or make a slower descent by using a lower gear.

Do not use the exhaust brake when driving on slippery or low traction road surfaces. Failure to follow this precaution could result in a loss of vehicle control and possible personal injury or property damage.

Exhaust Brake Operating Characteristics

When you remove your feet from both the accelerator and clutch pedals and the exhaust brake switch is in the on position, the exhaust brake is applied. The following conditions should exist if the brake is operating properly:

A slight change in the sound of the engine may be noticed when the exhaust brake is applied.

Exhaust smoke should appear normal.

Engine temperature should remain in the normal operating range.

Road speed usually decreases when the exhaust brake is applied during a descent. When the vehicle is carrying a heavy load or the grade is extremely steep, you may need to apply the service brakes occasionally.

Do not expect a retarding effect similar to sudden hard application of the service brakes. The exhaust brake retards the vehicle with a smooth braking effect.

During a descent, the tachometer usually shows a drop in rpm depending on the grade and the vehicle load.

Depending on the grade and vehicle load, you may or may not feel the retarding force acting against your body when the brake is applied. The retarding force of the brake may not always be noticed, but it is actually preventing the vehicle from going much faster.

Shutting Off the Engine

Make sure the exhaust brake is turned off before shutting off the engine.

Pacbrake® Exhaust Brake

The Pacbrake exhaust brake is intended as a supplement to the service brakes and will not bring the vehicle to a complete stop. The Pacbrake will assist in the control or reduction of road speed in conjunction with, or independent of, the service brakes. The amount of retarding or braking force is controlled by the driver.

Pacbrake Operation

The Pacbrake is controlled by the exhaust brake switch and the throttle pedal. All applications are additionally affected, controlled, or governed by engine speed through transmission gear selection. The Allison MD3060 transmission has automatic downshifting when the exhaust brake is requested. See the information on the "Allison World Transmission" later in this chapter.

On some applications, when the Pacbrake is in use, it may be necessary to check that the cruise control is not set and that the throttle is in the idle position.

On some applications the engine, transmission, cruise control, and the Pacbrake exhaust brake may electronically interact with each other, which automatically operates their functions. Following are some examples of the programmed options that may be available with the cruise control in the on position:

The coast mode engages the Pacbrake when the service brake is applied and disengages when the service brake is released.

The latch mode engages the Pacbrake when the service brake is applied and the Pacbrake remains on after the service brake is released. The Pacbrake is disengaged when another input (depressing the throttle or clutch, engine speed drops below 800 rpm, or the exhaust brake switch is turned off) is supplied.

The manual mode does not require the cruise control switch to be on and operates the Pacbrake manually at the driver's discretion.

The amount of braking power the engine will develop is related to the speed (rpm) of the engine. The higher the engine rpm, the greater the retarding power.

Certain conditions may require that the transmission be downshifted in order to generate adequate rpm for the amount of retarding power required. Pacbrake exhaust brakes are designed and approved for safe use at 300 rpm above the engine's maximum governed rpm. Refer to individual engine manufacturer's specifications.

The Pacbrake will function best if it is used all of the time. However, if the vehicle is used inconsistently or seasonally, it may be necessary to perform a preventive maintenance procedure.

1.

With the engine shut-down, use any oil-free or nonpetroleum based high-heat lubricant and spray or coat a sufficient amount on the restricter valve shaft and the attaching locations at each end of the actuation cylinder. See Fig. 4.5 .

A. Lubrication Point

Fig. 4.5, Pacbrake Exhaust Brake and Air Cylinder

2.

With your hands or a pair of pliers, motion the valve several times to distribute the lubricant down the shaft and the attaching locations.

NOTE: Starting the engine and idling for short periods of time is not recommended. During a cold engine start-up, enough moisture is developed within the engine and the exhaust system to create a corrosion hazard that could affect the future operation of the Pacbrake. The brake housing may trap water in the valve shaft bore causing corrosion in an improper or nonfunctioning brake. If it is necessary to periodically start the engine, it is recommended that normal operating temperatures be attained before shutting down the engine.

Allison World Transmission

Pacbrake exhaust brakes on engines that are used with the Allison World Transmission MD series, are interfaced with the transmission electronic control module (ECM). An exhaust brake enabled transmission ECM will usually provide converter lockup in gears two through six. Effective exhaust braking begins when the transmission automatically downshifts into fifth gear (62 mph or less). Once on, the Pacbrake exhaust brake will control road speed and/or slow the vehicle sufficiently that the transmission will automatically downshift, if necessary, to Allison's preselect mode.

The preselect mode is normally assigned to second gear; however, the transmission can be reprogrammed by an Allison Transmission Distributor to third or fourth gear should the operator desire. If additional retarding power is required before the automatic downshifting occurs, you can select a lower transmission gear on the Allison shift selector.