Hello all, I understand doing a compression test on an engine at running temp. But, can oil seepage past the valve seals/guides falsify the test? I know you first take a reading of compression dry and then squirt some oil in the cyl. to get a wet reading to differentiate between rings and valves etc. But does the possibility of oil past the seals/guides that much of a concern and does it make the reading false. I know compression testing has been done for years, if this is a possibility then wouldn't all tests be void with any motor that has mileage on it? Thanks. John

I dont think that will make a diff... The amount of oil is too small. unless the return passage is clogged :)

I didn't think it would make much of a difference unless oil is pouring past the seals/guides! John

Actually when your doing a compression test, your checking the condition of your rings. Adding the oil, wet test, is to see if your compression goes up. If it goes up considerable, you have bad rings or worn cylinders.
If you want to do a cheack to pin point the area that causing low compression, either rings, valves, valve guides, you need to do a leakdown test, it is much or acurrate.:skull: