How to know if its Valve Stem Oil Seals or Piston Rings?

My car blows blue smoke when its been idle for a while then it stops while im driving...How do i figure out which one it needs. I know I have a real main seal leak but that wouldn't cause blue exsaust smoke would it?? I have a 1997 Mitsubishi Eclipse with 187 miles...Mainly highway miles.How to know if its Valve Stem Oil Seals or Piston Rings?
1. Your car does not have valve sem seals. Even if seals were installed it would not fix the real problem. Blue smoke out the back on deceleration and when you first start the car means the valve guide clearance is loose. The clearance between the valve stems and the valve guide is usually .001 -.0015 on the intake valves and .0015 -.0017 on the exhaust valves. If the car does not use an unusual amount of oil or foul spark plugs don't bother with the expensive valve guide replacement repair.If you use more than a quart of oil per 1000 miles and the car is in otherwise good shape get it fixed by an independant mechanic. It'll take some outside machine work to drill oversize all the valve guides and new ones pressed in place. This job also requires re-grinding the valves and seats for a perfect valve seal.





Piston ring problems usually cause blue smoke 100% of the time while driving the car.





A dry compression test will tell if the rings are bad. The second test involves a shot of motor oil in a the spark plug hole being tested. If the compression goes up there is a valve problem. If it stays down it's a ring problem.How to know if its Valve Stem Oil Seals or Piston Rings?
comment on above answer....





that is all true except the last part: if u squirt oil into the cylinder %26amp; do the compression test again, if the compression goes up, it shows a ring problem, not a valve problem. And if it doesnt go up after u squirt oil in it, it's either super worn rings or bad valve Report Abuse

sounds like valve seals, but you could test the compression on each of the cylinders to see if you have loss of compression, (rings) And your right, the rear main seal wouldnt cause that....... you can get a compression tester anywhere, even wal mart!
you could get a compression test.


A good mechanic can figure it out.


Most likely the oil is pooling in the valve cover and its dripping thru the valves worn rubber seals.
Rings smoke all time usually more on acceleration. Valve seals smoke worst on 1st start up.






if it only smokes when you start it up it is bad valve seals, with that many miles on the engine the whole engine needs redone.
with 187,00 miles my guess is the engine is tired and needs to be replaced or rebuilt.