Curious, oil smoke..........

[Dr. Righteous]

Greets all.

Last week I purchased a '94 Jeep Grand Cherokee Limited on the cheap.
A bit rough around the edges, but overall good shape. Many things were let go, but nothing that isn't easy to fix. 4.0L I6, known for running forever. Didn't see any oil smoke, and had great power and good mileage. No reason to think there was a problem. The only thing I noticed wrong was that the PCC (same as a PCV on a V8 but no check valve) was shot, all rubber, tubes were bad. Would smell oil when I drove it. Also the valve cover gasket was bad so those was first thing I fixed. When I had the valve cover off I looked for gum and other signs of no oil changes. It didn't look bad. Wasn't gummed up, I could read the casting numbers on the cylinder head. About what you would expect to see for a 100K+ engine.
I noticed it consumed about 1/2 quart on a 500 mile trip but I chalked it up to a non working PCC system, but still NEVER saw any smoke from the tailpipe. I tuned it up this weekend, plugs, wires, cap, rotor , everything. The plugs were very worn, and ashy like it was consuming oil. After I did the ignition stuff I charged the AC. It sat idling for probably 20 minutes. I noticed some blue smoke coming from the tail pipe. BURNING OIL, that is bad news. After I finished the AC I took it for a test drive. It ran much smoother better because of the worn out ignition parts, AC was ice cold. I kept my eye on the rear view mirror when I stopped at lights to watch for smoke as well as when I was driving. Never saw any. I got back home and let it sit and idle a while and still didn't see any at first. But it seems if it sits idling long enough, here comes the smoke.
In my experience, when there is enough wear for blue smoke, engine power is way down and gas mileage is bad. Not in this case. I have not done a compression check yet, but that is next. I was actually SHOCKED to see it smoking. It just runs very well and 122K miles is LOW for one of these. I had a '91 XJ Jeep with the 4.0L that I put 220K HARD miles on it and it used no oil and still ran fantastic. Will check the compression to see what that reads. I don't expect it to be too far out because of how well this things runs.

Any ideas??

[creative1]

valve guides and/or seals would be my first guess. i dont know anything about those engines, but that would be my guess. if it was rings, you would see oil smoke when stepping on the go pedal.

[Dr. Righteous]

Yeah, with worn guide or bad seals I would expect a lot of cold smoke. There is none. Only after warmup and idle. Have to run camera at Church tonight so I don't know if I can do a compression check this after noon, but tomorrow for sure.

[TK]

you can replace teh guid seals on the 4.0 by removing the rocker cover and the plugs do a leak down compression test though, see if it has some compression loss thrue teh valves. re-man heads for the 4.0 are pretty cheap