Hi all,
I own an '02 Outback Limited with the manual transmission. The car has almost 180k on it and I've owned it since August 2020, when it had 163k on it. In the entire time I've owned the car, it has consumed oil...I'd say about a quart every 800 miles. What's weird though is that when I check the dipstick (engine cool, flat surface, pull out, wipe clean, reinsert, and check the level), it will read full, full, full, full, full, and then all of sudden will have nothing on it. For instance, on my first oil change with this car, I'd checked the dipstick just 2 days before I had the oil changed. It was full. When I got the oil changed, the shop said there was no oil in the car (!) (meanwhile, no ticking or overheating or oil light). Fast forward to last June, when I had a leaky valve cover gasket replaced, a compression test, and a leak down test before a cross country road trip (1500 miles on which the car did not burn oil, although it did on the way home, following the same route...). Now, oil consumption seems to have gotten a lot worse, about twice as bad. I'd heard seafoam and MMO could help with this if I just had stuck piston rings or whatever, so I used a can of seafoam spray and I've changed the oil 2 or 3x now every 300 miles using 20% MMO. This doesn't seem to have helped at all. The car definitely uses more oil when MMO is in it (I guess because it is so thin?) (I made it about 200 miles before I needed to add more). When using MMO, I first coupled it with conventional 5w-30 (what I usually use), but last time tried with 10w-40 (it actually went through the oil faster). I'm going to try today just going back to 100% 5w-30, but still, this seems really excessive. I can't smell anything unusual when I'm driving, I can't see smoke out the tailpipe, I know the car passed the leakdown test, and while I don't remember the compression numbers I don't recall that my mechanic was concerned. He actually told me the oil consumption is normal. Any ideas on where in the world this oil is going and how I could fix it? I checked my PCV valve and it rattles. The other day, I had the car running with the hood open and for whatever reason the passenger side of the engine smoked slightly briefly, not sure if it was oil or what was going on. I am pretty new and inexperienced in the world of cars, just interested in it and trying to learn how to fix and take care of my ride.
Is it dripping from the head gaskets? You didn't say what engine you have, but that vintage of Subaru with 4-cylinder non-turbo engine is very prone to head gasket problems. They tend to leak externally before failing internally. If yours has that engine with original head gaskets they are overdue to fail. Also, is there oil residue on the spark plugs or in the tailpipe?
Another possible issue is valve stem seals. Those could certainly be shot after 20 years, permitting oil to be drawn down the valve stems into the combustion chambers.
Of course the engine just could be burning oil due to wear after 20 years and 180K miles. Oil control rings can wear before compression rings, which a compression or leakdown test is not going to detect.
