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How to Test for Compression Leaking Into the Cooling System

Your engine needs to be able to build and hold a great deal of compression in the combustion cylinders in order to operate properly. Additionally, compression in each of the cylinders needs to be within a small percentage range from highest to lowest. Compression can leak past one or both of the valves, which can be detected by a noticeable hissing sound in the exhaust or intake. Compression can also leak past the head gasket seals into the cooling system. This kind of leak needs to be found and fixed quickly, before it causes serious internal damage to your engine.

Instructions

1

Disconnect the spark plug wires at the plugs by gripping the plug and twisting while turning. Write the cylinder number on the plug boot to facilitate reassembly.

2

Rotate the spark plugs counterclockwise with the spark plug socket and ratchet to remove them. Use extensions and universal swivel as needed.

3

Thread the leakdown tester into the opening for the first spark plug. Remove the radiator cap by pressing down and turning it counterclockwise. Add the exhaust gas detector solution to the radiator coolant. Place the balloon or rubber glove over the radiator opening.

4

Turn the key to start and allow the engine to turn over about 10 times.

5

Check the glove or balloon to see if it appears to have filled at all. If so, you have determined there is a leak from the combustion chamber into the cooling system from number one cylinder. Write down the compression reading.

6

Repeat Steps 3, 4 and 5 until you have checked all of the cylinders in turn, checking the balloon/glove after each time you turn the engine over. Write down each of the compression readings.

7

Compare the compression readings from cylinder to cylinder. The reading should be around 150 pounds per square inch of compression, with a maximum variance of about 15 pounds per square inch from high to low readings.

8

Remove the balloon or glove from the radiator opening and inspect the coolant. Some exhaust gas leak kits will cause the coolant to change color in the presence of exhaust gasses. Others will have you look at the coolant using a special light.