Looks and runs like new still, except it suddenly started losing oil about a month ago. This vehicle was extremely well maintained, well beyond manufacturer recommendations. For just one example, oil changes were always at (not exceeding) 3,000 miles. For the first ~10 years (weekend runabout) conventional oil was used, 5W30 or 10W30. For the last year, it has been a commuter, and oil is still changed every 3,000 miles, but now synthetic blend 5W30 is used. Other maintenance done has all been expected, "scheduled" stuff like tires, a battery, air filters, spark plugs, a couple brake jobs, stuff like that.
EVERY 3,000 miles, the engine would "use" about 1/2 to 3/4 quart of oil between 3,000 mile oil changes. (nothing odd)
Around mid-February, I checked the oil at around 1500 miles past last oil change (synthetic blend 5W30) It was a half quart low. That didn't bother me. The fact that it was PITCH BLACK did. That was unusual for this car. Oil does get darker/discolored, but I've never seen it black before. Didn't think too much about it. Dumped a half-quart of regular 10W30 in (what I had handy). A week later (and another ~300 miles), I checked the oil again and it was A FULL QUART LOW. Since that time, it has lost (for lack of a better word) a full quart of oil every 250 miles.
Obviously there's a problem. Now here is what has the mechanics stumped. Several good mechanics have looked at this car. These are the facts known so far:
1) There are NO oil leaks. I confirmed this myself, but several mechanics have had it up on the lift and can not find even a minor oil leak. I would expect the underside of the car to be covered in oil if oil was leaking at a rate of 1QT/250miles , but there's no oil at all down there, that anyone can find. My garage floor is oil free. My parking spot at work is oil free. 2) There are no problem codes in the computer. 3) Car starts easily and runs well, but sometimes hesitates on acceleration above about 2000RPM or so (that started around the same time that the excessive oil consumption started) 4) Engine easily passed emissions test while losing oil. In fact, the mechanic who tested emissions noticed the engine was again a full quart low, and added oil. 5) Several (dry) compression tests have been run since oil started disappearing. Numbers on all cylinders on all tests range from 190 - 195 (a couple of 200 readings in there somewhere also). According to Mitsubishi, this is good. According to all mechanics I have consulted, this is very good. The last compression test done, I witnessed myself. I read the gauges as (cylinders 1 - 4) 195 - 195 - 190 - 190. A "wet" compression test was also done at one point, and I was told that it was GOOD, but don't remember the readings. Other mechanics have told me that the wet test was redundant anyway. (because the dry test looked good) 6) One mechanic told me that there's no oil inside the tailpipe. I guess that's good? 7) Car has sat for several days (once) after excessive oil consumption started. While sitting (not driven), it apparently lost no oil. 8) In desperation, one mechanic drained out the synthetic blend 5W30, changed the oil filter, then refilled the engine with * 15W40 * conventional oil. According to the Mitsubishi service manual, that is OK for the engine (it'll take from 5W30 up to 20W50?, or somewhere there). But, the thicker oil made no difference. The car still loses a quart of oil every 250 miles, when driven.To put it bluntly, where the HELL is the oil going? I'm kind of attached to the car, so I'll throw money at it. But first I need to know what the problem IS. I'm stumped. Several good mechanics are stumped. No rings or valve problems, no oil leak, emissions good, exhaust not discolored, but oil is disappearing at rate of 1 Quart every 250 miles. Is this a wierd Mitsubishi quirk that none of my mechanics have heard of? That is, makes oil disappear without burning it or leaking it???