During a cylinder leakage test, air escaping from the oil fill port indicates likely wear of which component?

• A. Worn or weak piston rings
• B. A burnt or poor sealing exhaust valve
• C. A burnt or poor sealing intake valve
• D. Cylinder liner cavitation

Answer: (A)

Air escaping from the oil fill port during a cylinder leakage test points to blow-by past the piston rings. When the rings are worn or weak, compressed air in the cylinder can slip past the piston into the crankcase and then vent out through the oil fill/vent path. This is the telltale sign that the rings aren’t sealing well.

If air were leaking out of the exhaust or intake ports, that would indicate a burnt or poorly sealing valve (exhaust or intake, respectively). Cylinder liner cavitation isn’t tied to air leaking through the oil fill port, so it wouldn’t produce this symptom.