Oil in top of engine

[Maguire]

I have a 1986 Mercruiser 140 H.P motor. A lot of oil is going up through the small hose on top of valve cover and into carburetor and causing smoke. Cracked rings has been mentioned as a possibility but motor runs very well and plugs aren't fouled with oil ........don't know if any of that matters. Any help would be appreciated.

 

[mthieme]

Re: Oil in top of engine

It is blowby.
A cracked ring(s) is a probable cause. I recommend doing a dry then wet compression test which will tell you if it lower end or not.

 

[Maguire]

Re: Oil in top of engine

First off, Thanks for the reply. Hope you'll be patient with me here but I really don't know what I'm doing most of the time. By lower end do you mean the crankcase and pistons/rings etc. (the lower half of the motor)? When you say dry test/wet test does that mean test it right after I start it and then again after it has run for awhile and if the second test shows lower compression than the first, it is probably a ring/s? Am I close?

 

[Fishermark]

Re: Oil in top of engine

By lower end do you mean the crankcase and pistons/rings etc. (the lower half of the motor)?

Yep - in this case specfically the pistons / rings.

When you say dry test/wet test does that mean test it right after I start it and then again after it has run for awhile and if the second test shows lower compression than the first, it is probably a ring/s? Am I close?

Close? Well, kinda.

With the engine warmed up, pull all the plugs, open the carb throttle all the way, and do your compression test. That is a dry test.

After that test, put some oil down each spark plug hole and do the test again. (A teaspoon full or so). If the compression raises significantly, then it is your rings. If it doesn't, then it is in the upper end - the valves.