What does a compression test measure in an engine?

A compression test measures the pressure within the engine cylinders during the compression stroke. This test is critical for evaluating the health of the engine's internal components, specifically the pistons, piston rings, and valves.

When conducting a compression test, the goal is to assess how well the engine can compress the air-fuel mixture within the cylinder. A healthy engine will generate a specific range of pressure, indicating that the piston is sealing effectively against the cylinder walls and that the valves are functioning properly to allow for an adequate compression cycle. Low compression readings can indicate issues such as worn piston rings, leaky valves, or head gasket failures.

This process provides valuable insights into the engine's performance and helps diagnose various problems before they lead to more severe failures, making it an essential tool in automotive diagnostics and service.