Gray smoke and oil usage after warmed up

1994 XJ, 4.0 156K

I have done a search regarding the issue with blowby on these engines and I believe mine has an issue with the rings. I use an extensive amount of oil and after sitting at a light for awhile it starts enough blowing smoke out the tailpipe so that everyone nearby starts to stare. It seems to be limited to sitting at a long light (after it warms up) and does not noticeably smoke while driving, except right after a long red light.

The engine runs smooth and only has a light knock so I don't want to tear it apart to fix it right at this point.

I have no oil in the air cleaner and am wondering if the ccv vacuum hose has enough vacuum to suck the oil "mist" directly into the intake manifiold and out the tailpipe.

Does anyone have any idea on how to fix the smoke and oil usage symptom?

Rings will smoke under heavy load. Rings cause blowby and oil in the air box. Leakage around the valve guides is worse at high vacuum situations, like sitting at a light. Sounds like valve guides to me. Changing the valve seals may be a temporary solution but a valve job that includes sleeving the guides, not knurling the guides is the fix.

The sure fire way to tell is to drive it a while until it is warm then go sit in the drive through line at Burger King and let it idle. By the time you wait for a couple of cars and get to the window, it will look like you are spraying for bugs. :laugh3:

old_man said:

The sure fire way to tell is to drive it a while until it is warm then go sit in the drive through line at Burger King and let it idle. By the time you wait for a couple of cars and get to the window, it will look like you are spraying for bugs. :laugh3:

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Hmmm. That's sounds pretty familiar. Can seals on the 4.0 be done w/o pulling the head? What are the issues with doing head only at 156K?

valve seals are easily done with the head on. You need basic hand tools (decent socket set), an air compressor, an adapter to connect the air to the spark plug hole and a spring compressor made for in-car repair. having a service manual of some kind will be helpful

If you have a shop do it, it should about 300 bucks. give or take.

Not to say that it hasn't been done successfully, but at156k, a valve job is not a good idea as it can hasten ring failure in a worn engine.

A leakdown test will confirm the cylinder seal. If the leakdown rate is less than 20% and all cylinders are within 2 or 3% the bottom is most likely ok..I very rarely have seen the compression rings pass, and the oil control rings fail.

If the bottom end passes, the culprit is as Tom said....the valve guides and/or seals. And if you have the head refurbished...don't let anyone talk you into knurling the worn guides (unless you plan to sell your rig pretty quick) spend the extra bux and have the job done properly.