Automotive Service Excellence (ASE) A8 Engine PerformanceGeneral Engine DiagnosisEasy
A technician performs a 'wet' compression test on cylinder #3 after a 'dry' test showed a significantly low reading. The dry reading was 90 psi, and the wet reading is 140 psi. What does this result indicate?
- AA leaking intake valve.
- BWorn piston rings.
- CA blown head gasket.
- DA cracked cylinder head.
Show answer & explanationAnswer & explanation
Correct answer: B. Worn piston rings.
When a small amount of oil is added to a cylinder and the compression significantly increases during a wet compression test, it indicates that the oil is temporarily sealing worn piston rings, thereby improving compression.
Why the other options are wrong
- A. A leaking intake valve's compression would not significantly improve with the addition of oil, as the oil would not seal the valve seat.
- C. A blown head gasket's compression would not significantly improve with the addition of oil, as the oil would not seal the gasket leak.
- D. A cracked cylinder head, depending on its location, could cause various issues, but its compression would not typically be significantly improved by adding oil to the cylinder.
Wet Compression Test - Worn Rings
A diagnostic test where a small amount of oil is added to a cylinder to see if compression improves, indicating worn piston rings.
- Significant compression increase (typically >10-20%) points to ring wear.
- If compression does not improve, valve or head gasket issues are more likely.
- Follows a dry compression test on a low cylinder.
Memory trick: Wet Test, High Score? Rings are Worn, nothing more!