What information is gained from a compression test?
A compression test reveals the condition of your engine’s valves, its valve seats, and piston rings and whether these parts are wearing evenly. Healthy engines should have compression over 100 psi per cylinder, with no more than 10 percent variation between the highest and lowest readings.
What causes low compression?
Exhaust valves and air intake valves at the top of the cylinder can also get overheated, and leak gas or the valve seals can become too worn to seal the gas in properly. Either way, the result is often low compression. Several valve problems can lead to low compression. For one, you may have a dropped valve seat.
How do you test cylinder compression?
If a cylinder has low compression, perform a wet compression test to indicate whether it’s a bad valve, head gasket, or worn piston rings causing the problem. To perform this test, inject about a teaspoon of oil into the weak cylinder through the spark plug hole and screw the compression gauge back in.
What is a good compression test result?
Good compression test results indicate that the engine does not have a compression-related problem at the moment—and that’s about all. The thing is this: Any mechanic worth his weight in salt should already know that something is wrong with the engine prior to doing a compression test.
What can cause high compression on one cylinder?
Another possibility is a broken camshaft in the area that operates valves for two adjacent cylinders. Furthermore, The engine compression could be too high in one or more cylinders. This would be an indication of excessive carbon buildup in the engine.
What does an engine compression test tell you?
An engine compression test will tell you many things about the mechanical condition of your engine. The test can detect, for example, pressure leaks through rings, cylinders, valves, or a head gasket without taking apart the engine.