Instruments
The instruments are listed here in alphabetical order, to make the information easier to find.
Note: Some of the listed instruments are optional, and not found in every vehicle.
Air Intake Restriction Gauge
The air intake restriction gauge indicates the vacuum on the engine side of the air cleaner. On standard installations, it is mounted on the air intake duct in the engine compartment, and has a go/no-go restriction indicator without graduations. See Fig.. As an option, a graduated indicator (see Fig.) on the air intake duct or, for easier viewing, a dash-mounted restriction gauge may be installed.
Fig. 1, Manual-Reset Air Restriction Indicator, Go/No-Go
Fig. 2, Air Intake Restriction Indicator, Graduated
Air intake restriction vacuum is measured in inches of water (inH2O). For vehicles equipped with a graduated indicator or a restriction gauge on the dash, check the gauge with the engine off. If the yellow signal stays locked in the red zone once the engine is shut down, or is at or above the values shown in Table 4.2, the air cleaner element needs to be replaced.
Note: Rain or snow can wet the filter and cause a temporary high reading.
Table 1, Air Intake Maximum Restriction Values
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Air Intake Maximum Restriction Values (inH2O) |
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Engine Make |
GHG14, GHG17, and GHG21 Engines |
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Detroit |
18 |
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Cummins |
25 |
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Table 1, Air Intake Maximum Restriction Values
Application Air Pressure Gauge
An application air pressure gauge (see Fig.) registers the air pressure being used to apply the brakes, and should be used for reference only. The gauge will not register air pressure until the foot brake pedal is depressed or the trailer hand brake is applied.
Fig. 3, Application Air Pressure Gauge
Coolant Temperature Gauge
Notice: A sudden increase in coolant temperature may indicate engine or cooling system failure. Bring the vehicle to a safe stop and investigate the cause to prevent further damage. Do not operate the engine until the cause has been determined and corrected.
During normal engine operation, the coolant temperature gauge (see Fig.) should read 175 to 195°F (79 to 91°C). If the temperature remains below 160°F (71°C), inspect the cooling system to determine the cause.
Fig. 4, Tachometer and Coolant Temperature Gauge
For Detroit engines, if coolant temperature rises above 215°F (101°C), the CHECK engine lamp will illuminate. If the condition does not improve, the STOP engine lamp will also illuminate and an audible warning will sound. The engine will then derate or shut down, depending on the type of engine protection system installed.
Drive Axle Oil Temperature Gauges
Notice: A sudden increase in oil temperature that is not caused by a load increase may indicate mechanical failure. Bring the vehicle to a safe stop and investigate the cause to prevent further damage. Do not operate the vehicle until the cause has been determined and corrected.
During normal operation, drive axle oil temperature gauges (see Fig.) should read as follows:
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160 to 220°F (71 to 104°C) for Detroit Classic Model 2, 4, and 6 axles.
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160 to 329°F (71 to 165°C) for Detroit New Final Drive (NFD) axles.
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160 to 275°F (71 to 135°C) for Meritor™ drive axles.
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180 to 200°F (82 to 93°C) for Dana Spicer® drive axles.
Fig. 5, Drive Axle Oil Temperature Gauge (rear drive axle gauge shown)
Under heavy loads, such as when climbing steep grades, temperatures that exceed the normal oil temperature range for a short period are not unusual. If the temperature returns to normal when the load decreases, there is no problem.
Engine Oil Pressure Gauge
Notice: A sudden decrease or absence of oil pressure may indicate mechanical failure. Bring the vehicle to a safe stop and investigate the cause to prevent further damage. Do not operate the engine until the cause has been determined and corrected.
The engine oil pressure gauge, as shown in Fig., displays the current engine oil pressure. If engine oil pressure falls below the minimum levels shown in Table., the CHECK engine lamp will illuminate. If the condition does not improve, the STOP engine lamp will also illuminate and an audible warning will sound. The engine will then derate or shut down, depending on the type of engine protection system installed.
Note: Oil pressures in See Table. are given with the engine at operating temperature. With the engine cold, oil pressure may be higher. Individual engines may vary from the listed pressures; observe and record pressures when the engine is new to create a guide for checking engine condition.
Fig. 6, Speedometer and Engine Oil Pressure Gauge
Table 2, Minimum Engine Oil Pressure
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Minimum Oil Pressure |
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Engine Model |
At Idle Speed: psi (kPa) |
At Rated RPM: psi (kPa) |
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Detroit |
14 (97) |
55 (350) |
Table 2, Minimum Engine Oil Pressure
Engine Oil Temperature Gauge
Notice: A sudden increase in oil temperature that is not caused by a load increase may indicate mechanical failure. Bring the vehicle to a safe stop and investigate the cause to prevent further damage. Do not operate the engine until the cause has been determined and corrected.
During normal operation, the optional engine oil temperature gauge (see Fig.) should read in the following temperature range:
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200 to 260°F (93 to 126°C) for Detroit engines
Under heavy loads, such as when climbing steep grades, temperatures that exceed the normal oil temperature range for a short period are not unusual. If the temperature returns to normal when the load decreases, there is no problem.
Fig. 7, Engine Oil Temperature Gauge
Fuel/Diesel Exhaust Fluid (DEF) Gauge
For engines that are EPA10-compliant or newer, the fuel and DEF levels are measured in a dual purpose fuel/DEF level gauge. See Fig..
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Diesel Fuel Level Indicator
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DEF Level Indicator
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Low DEF Warning Lamp (amber below 10% DEF)
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Low Fuel Warning Lamp (amber at 1/8 tank of fuel)
Fig. 8, Fuel/DEF Gauge, EPA10 and Newer
The diesel fuel level is indicated at the top of the gauge, with a low-fuel warning lamp that illuminates amber when the diesel fuel level registers 1/8th of capacity.
The DEF level is indicated in a four-segment lightbar on the lower portion of the gauge. There is a low DEF level warning lamp that illuminates amber when the DEF level reaches 10% of capacity. See Greenhouse Gas Emissions and Fuel Consumption Standards for details of the DEF gauge functions.
Primary and Secondary Air Pressure Gauges
Warning: If air pressure falls below minimum pressure, the braking ability of the vehicle will be limited. Slow the vehicle down and bring it to a gradual stop. Do not attempt to move the vehicle until air pressure has risen above the minimum level. Moving a vehicle without adequate braking power could cause an accident resulting in property damage, personal injury, or death.
Air pressure gauges (see Fig.) register the pressure in the primary and secondary air systems. Normal pressure, with the engine running, is 100 to 120 psi (689 to 827 kPa) in both systems.
Fig. 9, Air Pressure Gauge (primary shown)
A low-air-pressure warning light and audible alert, connected to both the primary and secondary systems, activate when air pressure in either system drops below approximately 70 psi (483 kPa).
When the engine is started, the warning light and audible warning remain on until air pressure in both systems exceeds minimum pressure.
Speedometer
Two speedometer options are available. The U.S. version of the speedometer (see Fig.) registers speed in both miles per hour (mph) and kilometers per hour (km/h), with mph in larger numbers. The metric version of the speedometer face reverses this arrangement, with km/h in larger numbers.
Suspension Air Pressure Gauge
A suspension air pressure gauge (see Fig.) registers the air pressure applied to the vehicle air suspension.
Fig. 10, Suspension Air Pressure Gauge
Tachometer
The tachometer (see Fig.) indicates engine speed in revolutions per minute (rpm) and serves as a guide for shifting the transmission and keeping the engine in the appropriate rpm range. For low idle and rated rpm, see the engine identification plate.
Transmission Fluid Temperature Gauge
The transmission fluid temperature gauge, shown in Fig., measures the transmission lubricant operating temperature. Temperatures vary by application, but the transmission fluid temperature gauge reading should not exceed 250°F (121°C).
Fig. 11, Transmission Fluid Temperature Gauge
Notice: A sudden increase in transmission fluid temperature that is not caused by a load increase may indicate mechanical failure. Bring the vehicle to a safe stop and investigate the cause to prevent further damage. Do not operate the vehicle until the cause has been determined and corrected.
Under heavy loads, such as when climbing steep grades, temperatures that exceed the normal oil temperature range for a short period are not unusual. If the temperature returns to normal when the load decreases, there is no problem.
Turbocharger Boost Pressure Gauge
A turbocharger boost pressure gauge (see Fig.) indicates the pressure in the intake manifold, in excess of atmospheric pressure, being created by the turbocharger.
Fig. 12, Turbocharger Boost Pressure Gauge
Voltmeter
The voltmeter indicates the vehicle charging system voltage when the engine is running and the battery voltage when the engine is off. By monitoring the voltmeter, the driver can stay aware of potential battery charging problems and have them fixed before the batteries discharge enough to create starting difficulties. A digital voltage display is integrated with driver message center. An optional voltmeter gauge (see Fig.) may be installed.
Fig. 13, Voltmeter
The voltmeter will normally show approximately 13.7 to 14.1 volts when the engine is running. The voltage of a fully charged battery is 12.7 to 12.8 volts when the engine is off. Battery voltage under 12.0 volts is considered a low battery, and a completely discharged battery will produce only about 11.0 volts.
If the voltmeter shows an undercharged or overcharged condition for an extended period, have the charging system and batteries checked at an authorized Western Star service facility.
On a vehicle equipped with a battery isolator system, the voltmeter measures the average voltage of all the batteries when the engine is running. When the engine is off, the voltmeter shows only the isolated battery voltage and does not indicate the voltage of the engine-starting batteries.