What does a compression test measure in an engine?

A compression test is an essential diagnostic tool used to evaluate the sealing effectiveness of an engine's cylinders. When performing this test, the technician measures the pressure generated within each cylinder when the engine is cranked. If the cylinders are sealing properly, they should reach a specific pressure level, indicating that the piston rings, valves, and head gaskets are functioning correctly.

A low compression reading in one or more cylinders can suggest issues such as worn piston rings, leaking valves, or a blown head gasket. Therefore, this test helps identify potential problems that could affect engine performance and the overall health of the engine. Understanding compression readings allows technicians to determine if further repairs are necessary to ensure optimal engine function.

The other options focus on different aspects of engine performance or function that are unrelated to the purpose of a compression test. Fuel efficiency relates to how effectively an engine uses fuel but is not measured by compression. The engine coolant temperature is important for maintaining optimal operating conditions but is measured separately, and the level of exhaust gas recirculation pertains to emissions control rather than cylinder compression.