Cooling System Pressure Test

Engine Cooling







Component Tests

Cooling System Pressure Test

WARNING: Always allow the engine to cool before opening the cooling system. Do not unscrew the coolant pressure relief cap when the engine is operating or the cooling system is hot. The cooling system is under pressure; steam and hot liquid can come out forcefully when the cap is loosened slightly. Failure to follow these instructions may result in serious personal injury.

NOTE: Vehicles with a degas bottle system have the pressure relief cap on the degas bottle and no radiator cap.

1. Turn the engine OFF.

2. Check the engine coolant level. Adjust the coolant level as necessary.






3. Attach the Radiator/Heater Core Pressure Tester from the Pressure Test Kit to the degas bottle nipple and overflow hose. Install a pressure test pump to the quick-connect fitting of the test adapter.

4. NOTICE: Do not pressurize the cooling system beyond the maximum pressure listed in the specifications table or cooling system components can be damaged.

NOTE: If the plunger of the pressure tester is depressed too fast, an erroneous pressure reading will result.

Slowly depress the plunger of the pressure test pump until the pressure gauge reading stops increasing and note the highest pressure reading obtained. If the pressure reading exceeds the maximum cap pressure listed in the specifications table, install a new pressure relief cap.

5. If the system does not hold pressure, remove the pressure relief cap and wash in clean water to dislodge all the foreign material from the gasket. Check the sealing surface in the filler neck of the degas bottle for nicks or cuts. Install the pressure relief cap.

6. Pressurize the engine cooling system as described in Step 4 above. Observe the gauge reading for approximately 2 minutes. Pressure should not drop during this time. If the pressure drops within this time, inspect for leaks and repair as necessary.

7. If no leaks are found and the pressure drops. the pressure relief cap may be leaking. Install a new pressure relief cap and retest the system.

8. If no leaks are found after a new pressure relief cap is installed, and the pressure drops, the leak may be internal to the radiator transmission cooler (if equipped). Inspect the coolant for transmission fluid and the transmission fluid for coolant. Repair as necessary.

9. If the vehicle is equipped with a 6.4L diesel engine and no leaks are found and the pressure drops, the leak may be in one of the EGR coolers. Carry out the following steps.

1. Remove the outlet EGR temperature sensor and inspect inside the cooler for signs of coolant. Refer to Computers and Control Systems.

2. NOTICE: The vertical and horizontal Exhaust Gas Recirculation (EGR) coolers use gaskets of similar design but different material. Make sure the gaskets are used in their correct locations or the EGR coolers can leak.

NOTE: Do not disconnect any coolant hoses.

If signs of coolant are evident, separate the vertical EGR cooler from the horizontal EGR cooler, taking care not to bend the vertical EGR cooler bellows.

3. Pressurize the cooling system as outlined above. Check for evidence of coolant at the horizontal cooler.

4. Remove the suspect EGR cooler. Carry out the EGR cooler pressure test. Refer to Emission Control Systems.

10. If there is no contamination of the coolant or transmission fluid, the leak may be internal to the engine. Inspect the coolant for engine oil and the engine oil for coolant. Refer to Engine to diagnose the engine.

11. Release the system pressure by loosening the pressure relief cap. Check the coolant level and adjust as necessary.