As the title states, I have a mysterious oil usage phenomenon. When I fill up my gas tank I always check my oil, and if the Jeep has been driven locally it uses about half a quart. But, on long highway distances it uses almost a full quart. Funny thing is, there are NO leaks that are evident, anywhere, except for the power steering. I have taken my creeper and my Might-D Light LED light under there and inspected every inch that I can see, and bottom of motor (and transmission) is dry, plus there are no leak spots on clean concrete or pavement, and the plugs are clean and normal. The only leak that I have found was a minor one from the power steering cooler line, and a left outer CV shaft boot that's starting to show signs of seepage. Otherwise, it's dry as a bone under there.
assuming with a 2002 kj your mileage is on higher end? Had similar experiences with kjs with very high mileage for work trucks burning up oil. Vehicles ran great, still plenty power/torgue, zero leaks, no smoke or any other obvious signs. Finally one workday, was able to determine cause of at least for these kjs: coworker was driving behind me in another truck in a busy highway interchange area and the 05kj i was driving was throwing heavy blue smoke he said, but only in quick fits as I was going heavy throttle to enter highway, lane changes, etc. But once back to easier rpm, or idling, no smoke at all, but I was constantly adding oil at fillups. The trucks actually ran really well still and for a very long time like this with us adding oil very frequently; with the overall fleet maintenance program being very poor. That was our experience.
I'd second the burn hypothesis. If you are convinced it's not dripping out somewhere then it really only leaves a burn-off. Only other things I've personally seen happen is valve cover leaking onto exhaust (near #6) but you'd usually smell that one.
"Hey, ya never know til you try." Kurt Russell-Big Trouble in Little China
I had recently checked my exhaust for soot or other build up. If a vehicle is burning up to a quart of oil every tank then there should be some oily residue in the exhaust pipe, but my findings indicate a normal burn. Plus, I have had my fiance follow me a few times, from the grocery store, from her boys baseball game, and to go get her oldest boys XJ, and she has never seen any smoke coming out of my exhaust. So with the combination of clean plugs, low soot content, and no smoke, I can rule out burning oil.
Another possibility is that it could be dripping while running or driving, but you would think that it would have some residual dripping after I park the Jeep, but still no drips have been found on the ground, or on a clean sheet of card board.
Just curious what air filter you are using, and how far you go between oil changes? If oil is disappearing, it's either leaking, or burning off. You may not see the smoke either. You also need to evaluate how old your PCV valve is, and do you have signs of oil in the pcv lines.
If you are going too long between oil changes, or in the past the engine has gone too long between oil changes, then you could have some sludge build up as well. BG 109 before an oil change, then followed with MOA may help.
My maintenance schedule is very good, but I can't say for the P.O. When I had run my VIN (to search my Jeep's history), I had came up with two previous owners. The last one before me was a private owner, the first one was a car rental agency out of Colorado from around the ski areas. I will take a look at the PCV system and look for oil sludge on my next oil change this weekend.