My car has been burning oil and runnin like ****. I know the compression is low on a couple cylinder. the cylinders are like 220 and a couple are 150. Now is there anyway of knowing if it is bad rings or something wrong with the heads? thanks
TGO Supporter
sure you're doing the test right? i've never saw 220psi before. anyway squirt soem oil in the low holes and if it raises the compression you have bad valve. 150 isn't bad, actually i'd think 150 would be a respectable number.
Supreme Member
As for the compression test, you first run all the cylinders in the normal fashion (all plugs out, coil disabled, choke and throttle held full open, crank each cylinder until max pressure reached, record each cylinder's pressure, etc.). That's the dry test. Then, you put a tablespoon or so of oil in the cylinders through the spark plug holes, turn the engine over a few times to spread it around the cylinder, and then repeat the compression test. If the rings are worn, the oil will tend to enhance the seal and raise the compression pressure significantly from the dry test. You have to do both in order for the wet test to have any meaning. If the dry test numbers are close cylinder-to-cylinder and where they should be (say 150 psi), and no significant change to the dry test, then everything's fine. If the dry test is low and the wet test is low, then you have valve sealing problems.
Per 5-7kid
Per 5-7kid
Supreme Member
220 psi is pretty common in a motor with an exhaust lobe rolled...
Don't forget, engine compression is an adiabatic process; so the temp inside the cyl rises (since essentially no heat escapes during the test) which makes the pressure always far higher than the static CR minus "leakage" from valves being open during part of the comp stroke would indicate.
150-165 is fairly typical of a stock CR motor with a stock cam in it. Those cyls are probably OK. One with 220 is fornicated.
Don't forget, engine compression is an adiabatic process; so the temp inside the cyl rises (since essentially no heat escapes during the test) which makes the pressure always far higher than the static CR minus "leakage" from valves being open during part of the comp stroke would indicate.
150-165 is fairly typical of a stock CR motor with a stock cam in it. Those cyls are probably OK. One with 220 is fornicated.
The engine is about 10:1 compression. I tested the passanger side and the 2,4, and 8 cylinders were right on 220, but the #6 was like 160. I know 220 sounds high and it shocked me but thats what it read. thanx for the info guys.