How is a wet compression test conducted?

A wet compression test is primarily intended to diagnose the condition of an engine's piston rings and cylinder walls. During this test, a small amount of oil is added to the cylinder through the spark plug hole. The purpose of introducing the oil is to create a temporary seal that can help determine if worn piston rings or a damaged cylinder wall are the sources of low compression.

When the compression test is then repeated after the oil is added, an increase in the measured compression indicates that the problem likely lies with the piston rings, as the oil helps to temporarily seal any gaps. This method is effective because if the compression remains low, it suggests that the issue could be more serious, such as valve problems or cylinder wall damage.

This method is distinct and specific compared to other practices that might involve changing fuel types, altering engine temperature, or replacing mechanical components. Those actions do not measure the same characteristics of the engine's internal condition that a wet compression test specifically targets.