Valve Stem

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.

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.

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