Engine Compression & Cooling System Tools

During a cylinder compression test, a cylinder reads low at 90 PSI. You squirt a teaspoon of oil into the spark plug hole and retest: compression jumps to 150 PSI. What does this diagnose?

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 Correct IncorrectThe oil temporarily coats and seals worn piston rings against the cylinder wall. If compression jumps significantly ('wet test'), the rings are likely worn. If compression stays low, a valve is likely burned or leaking.

During a cylinder compression test, a cylinder reads low at 90 PSI. You squirt a teaspoon of oil into the spark plug hole and retest: compression jumps to 150 PSI. What does this diagnose?

• A cracked intake manifold
• A burned exhaust valve
• A clogged catalytic converter
• Worn piston rings or cylinder bore scoring (oil temporarily sealed the ring gap)