Cylinder Leakage Detection

Cylinder Leakage Detection

When a cylinder produces a low reading, use a leak detector to help pinpoint the exact cause. The leak detector is inserted in the spark plug hole, the piston is brought up to dead center on the compression stroke and compressed air is admitted. Once the combustion chamber is pressurized, read the percentage of leakage. Leakage exceeding 20 percent is excessive.

While the air pressure is retained in the cylinder, listen for the hiss of escaping air. A leak at the intake valve will be heard in the intake manifold and a leak at the exhaust valve and can be heard at the tail pipe. Leakage past the piston rings will be audible at the PCV connection or oil filler opening. If air is passing through a blown head gasket to an adjacent cylinder, the noise will be evident at the spark plug hole of the cylinder into which the air is leaking. Cracks in the cylinder block or gasket leakage into the cooling system may be detected by a stream of bubbles in the radiator.