Head gasket

When one is leaking? We always replace both of them. Whatever happened to one, . . . the other one is just as old and is likely to develop the same problem.

If you have a misfire problem, that is detected by the engine computer on 1996 and newer models. Reading the diagnostic fault codes will tell you which cylinder is misfiring.

If combustion gases are being pushed into the cooling system, usually coolant will go into the affected cylinder when the engine is stopped and there is still pressure in the cooling system. You can also use a cooling system pressure tester to keep the system pressurized. Remove the spark plugs, then watch which cylinder fills with coolant. This is not always conclusive because the fifteen pounds of pressure in the cooling system is not always enough to push a noticeable amount of coolant through the leak, while the much higher pressure in the combustion chamber can push gases into the cooling system.

You can also consider performing a cylinder leakage test. A compression test will tell you if a cylinder has low compression. A cylinder leakage test will tell you why it is low. Keep in mind head gasket leaks are usually so small, compression tests will look normal. The cylinder leakage test takes some time to perform. You bring the piston to top dead center on the compression stroke, then pump air in through the spark plug hole. That air goes through the tester which has a gauge that shows the percent leakage. More importantly, you can look in four places for the cause of the excessive leakage. You will hear hissing at the tail pipe if an exhaust valve is leaking. You will hear that at the throttle body if an intake valve is leaking. The hissing will be heard at the "oil" cap or dip stick tube if there is excessive leakage past the piston rings. If a head gasket is leaking into the cooling system, you will see a steady stream of tiny bubbles at the radiator cap.

You might find additional information here:

https://www.2carpros.com/articles/head-gasket-blown-test