Cylinder Leakage Test

When a cylinder produces a low reading, the use of Rotunda Engine Cylinder Leak Detection/ Air Pressurization Kit 303-F012 (014-00708) or equivalent will help pinpoint the source.

The leakage detector is inserted in the spark plug hole, the piston is brought up to top dead center on the compression stroke and compressed air is admitted.

Once the combustion chamber is pressurized, a special gauge will 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 by the intake valve will be heard in the throttle body area. A leak by the exhaust valve can be heard at the tail pipe. Leakage past the rings will be audible at the Positive Crankcase Ventilation (PCV) connection. If air is passing through a blown gasket to an adjacent cylinder, the noise will be evident at the 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 degas coolant bottle.