Dry test first

Start with a normal dry compression test on every cylinder using a consistent procedure. Record the numbers, crank count, throttle position, and battery condition so the comparison is meaningful.

What the wet test adds

Adding a small amount of oil can temporarily improve ring sealing. If pressure rises significantly, worn rings or cylinder-wall sealing become more likely. If pressure does not change much, valves, head gasket, cam timing, or test setup may deserve attention.

Tool setup

Use a compression tester with the correct adapter, a readable gauge, a hose that reaches safely, and a release valve for repeat testing. Avoid over-oiling the cylinder because it can distort the result and create mess.

Next diagnostic step

Compression numbers are clues, not a full diagnosis. A leak-down test, borescope inspection, cooling-system pressure test, or scan data may be needed before expensive engine work.

Frequently asked questions

Do you do wet or dry compression test first?

Do the dry test first, then use a wet test only to add context for low cylinders.

Does a wet test prove bad rings?

It can point toward ring sealing, but it should be confirmed with other evidence.

Can too much oil affect the result?

Yes. Too much oil can distort readings and create cleanup or safety problems.

Best next page

Use the Compression Testers guide when this diagnostic path points to a purchase decision. Compare job fit, limitations, compatibility, and the cost of ownership before choosing a model.

Open Compression Testers guide

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