What would cause low compression readings on only two adjacent cylinders in a compression test?

What would cause low compression readings on only two adjacent cylinders in a compression test?

• A. Worn piston rings
• B. Poor sealing liner O-rings
• C. Defective head gasket
• D. Cracked wet liner

Answer: (C)

When a compression test shows low readings in two neighboring cylinders, the leakage path is typically shared between those two chambers. The most common cause for that pattern is a defective head gasket between the two cylinders. If the gasket between adjacent cylinders fails, compressed air can leak from one cylinder into the other or into the cooling passages, so both cylinders register abnormally low compression when tested. Worn piston rings usually cause low compression in a single cylinder because the leakage path is around the piston in that bore. Poor sealing of liner O-rings tends to affect the cylinder with the liner, not necessarily its neighbor. A cracked wet liner can cause additional symptoms like coolant loss or mixing, rather than a clean two-adjacent-cylinder low reading pattern.

When a compression test shows low readings in two neighboring cylinders, the leakage path is typically shared between those two chambers. The most common cause for that pattern is a defective head gasket between the two cylinders. If the gasket between adjacent cylinders fails, compressed air can leak from one cylinder into the other or into the cooling passages, so both cylinders register abnormally low compression when tested.

Worn piston rings usually cause low compression in a single cylinder because the leakage path is around the piston in that bore. Poor sealing of liner O-rings tends to affect the cylinder with the liner, not necessarily its neighbor. A cracked wet liner can cause additional symptoms like coolant loss or mixing, rather than a clean two-adjacent-cylinder low reading pattern.