Which method can help identify a cylinder leaking combustion gases into the cooling system?

A cylinder leakage test is an effective method for identifying a cylinder leaking combustion gases into the cooling system because it directly measures the integrity of the engine's combustion chambers. In this test, compressed air is introduced into the cylinder at top dead center (TDC) of the compression stroke, and the technician monitors for any loss of pressure. If there is a leak, air will escape into areas such as the cooling system, crankcase, or out the exhaust, indicating a problem with the cylinder sealing.

This method provides a precise look at where the leakage may be occurring, determining whether it is due to issues like a blown head gasket, cracked cylinder head, or damaged piston rings.

While observing radiator coolant for bubbles can indicate the presence of combustion gases, it is not a definitive testing method. Similarly, a chemical vial sensitive to combustion gases can confirm the presence of hydrocarbons but does not localize the issue to a specific cylinder. An exhaust analyzer probe measures exhaust emissions but does not provide information on cylinder leakage directly. Therefore, the cylinder leakage test stands out as the most direct and reliable method for diagnosing a leak of combustion gases into the cooling system.