Pressure Relief Cap Check

p3 mm 20.01

Warning: Do not remove or loosen the surge tank cap until the engine and cooling system have completely cooled. Use extreme care when removing the cap. A sudden release of pressure from removing the cap prior to the system cooling can result in a surge of scalding coolant that could cause serious personal injury.

  1. Remove the surge tank filler cap first, to relieve the cooling system pressure, then remove the SAE cap; see Fig..

    1. SAE Cap (for coolant overflow pressure relief only)

    2. Surge Tank Filler Cap

    3. Cold Maximum Coolant Level

    4. Cold Minimum Coolant Level

    Fig. 1, Surge Tank

  2. Using a radiator-cap tester, check the pressure cap to see if it maintains pressure to within 10% of the pressure rating marked on the cap. If it does not, replace the cap. Make sure that the replacement radiator cap is correctly rated for the cooling system of the vehicle.
  3. There is a second valve in the pressure relief cap that opens under vacuum. This prevents the collapse of hoses and other parts that are not internally supported when the system cools. Inspect the vacuum-relief valve to be sure it is not stuck.
  4. Make sure that the filler cap seals properly on the coolant filler neck seat, and that the O-ring is not cracked or deteriorated. Replace the cap if the O-ring shows deterioration or damage.
Note:
Parent topic: Engine Cooling/Radiator
Document Number: 0000110988
Manual Publication Date: 2024-05-15
Topic Publication Date: 2024-11-22