Pressure Cap Test




Coolant system pressure tester

The pressure cap should be tested for the correct operating range every time the antifreeze is changed or any cooling system maintenance performed.


Do not remove the pressure cap when the engine is hot. The cooling system is under pressure and hot coolant and steam may escape causing severe burns. Allow engine to cool before servicing the cooling system.

1. See Figure 6-3. Using a cloth over pressure cap, turn cap 1/4 turn counterclockwise (CCW) to safety stop (2). Let pressure escape. Press down and turn cap to pass over safety stops and remove.

2. Inspect cap for gasket deterioration and broken springs.

3. Turn butterfly valve parallel to boss on COOLANT SYSTEM PRESSURE TESTER (HD-45335) tester head and turn pressure cap adapter onto tester head. Turn butterfly valve perpendicular to seal tester head.


To test new caps, wet the upper sealing gasket before turning onto adapter.

4. Turn pressure cap onto adapter. Rotate to safety stops.

5. See Figure 6-4. Pump handle to pressurize pressure limiting valve in cap. Stop pumping when pressure valve in cap opens.

6. Replace pressure cap if:

b. Opens above high limit, 124 kPa (18 psi).

c. Pressure falls rapidly when pressurized within range.

7. Open butterfly valve and remove adaptor and cap.

Figure 6-4. Pressure Cap Test
Do It Yourself Car Diagnosis

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