An engine compression test is one of the most reliable methods to determine the health of your engine. It measures the pressure created by the combustion of fuel inside the cylinders. Low compression can indicate worn piston rings, leaking valves, or head gasket issues, while uneven compression across cylinders often points to more serious internal problems.
Below, we provide a comprehensive engine compression test chart with common gasoline and diesel engines to help you quickly reference acceptable compression ranges.
Before using the chart, here’s a brief guide on how to conduct a compression test:
Warm up the engine – Compression readings are most accurate when the engine is at operating temperature.
Disable fuel and ignition systems – Prevent the engine from starting during the test.
Remove spark plugs or injectors – Depending on engine type.
Insert compression gauge – Screw the gauge into the cylinder spark plug hole.
Crank the engine – Turn the engine several revolutions (usually 4-5 seconds).
Record the reading – Repeat for all cylinders and compare against the chart.
Understanding Compression Test Results
Normal Compression: All cylinders within the manufacturer’s range.
Low Compression: Cylinder reading significantly below the recommended PSI (often 10-15% lower than others).
Uneven Compression: One cylinder differs substantially from the others. It can indicate leaks in valves, piston rings, or head gasket failure.
Zero or Near-Zero Compression: Often caused by a broken valve or piston damage.
Tips for Accurate Results
Test multiple times – Repeating the test ensures accurate readings.
Use a quality gauge – Cheap or worn-out gauges can give false readings.
Compare all cylinders – Even if one cylinder is low, it can affect engine performance.
Check for leaks – After testing, you can apply a small amount of oil in the cylinder. If compression improves, it usually indicates worn piston rings.
Final words
An engine compression test is a simple but effective diagnostic tool to assess your engine’s internal health. Using the compression test chart, you can quickly compare your readings against standard values for popular engines. Regular testing helps catch issues early, prevents costly repairs, and keeps your engine running efficiently.
Ryan Gary
With a solid foundation of 20 years in the mechanical industry and a Mechanical Engineering degree, Ryan Gary brings a deep understanding of automotive systems to Engine Oil Journal.
Driven by a passion for vehicles and a commitment to providing accurate information, he created this platform to empower drivers to make informed decisions about engine oil care.
