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Was it from too much oil?

One of my mechanic’s technicians accidentally put too much oil in my car ('99 Forester) during an oil change. About 600 miles later (and before I discovered the overfill), I had severe loss of power right after starting the car, as well as a big cloud of blue smoke from the tail pipe when I hit the gas. Once the car was completely heated up, the problem was limited to sluggish acceleration.



This would happen every time I started the car, until about a week after discovering the overfill and pumping out the excess oil, and the symptoms gradually diminished. Now it runs as it did before, with zero or minimal blue smoke.



So:

What the heck happened? Could this have all been caused by the oil overfill, and could there have been long-term damage?



PS: Also have the leaky head gasket (external leak only so far) that these cars are notorious for.



Appreciate any advice.

How much oil was added over and above the correct amount? Was it a quart or less, or was it 4 quarts, as if the engine had twice as much oil as it should have had?

This is important. A small amount of overfill won’t do any damage. If the engine were substantially overfull I’d think you would have noticed it before 600 miles.

Twice as much oil in the engine as there should be usually means something other than the engine (in Subarus it’s usually the transmission) was drained instead of the engine oil.

See where this is going? If someone drained the transmission fluid instead of the oil (happens all the time), then added the 4-5 quarts of oil the engine should have in it, the engine is WAY overfilled and the transmission is . . .

EMPTY, or nearly so.

I suggest you check the transmission fluid level ASAP.

No matter what, a simple check of the dipstick would have alerted you to this problem right away, instead of 600 miles later.

Now go check the transmission fluid.

Same thing happened to me a week ago. In the dealership they filled up my oil twice, naturally without checking the level the second time. I had 9 quarts instead of 5. After a couple of minutes I was driving with a plume of blue smoke behind me, the oil on the spark plugs was making the motor run poor, etc. At home I emptied all dealership oil (by the way, it was black) and replaced it with my favorite - Castrol. Driving improved immediately, but took a week to burn all junk and restore smooth engine operation.

And you didn’t complain about this, you just emptied the oil and did your own oil change?

As I recommended to Subariver, check the transmission fluid ASAP. Technicians often drain the tranny instead of the engine on Subarus, which is why the engines get filled with twice the oil they should have. The dirty oil never gets drained (you said it was black), but new oil is added, and the transmission might be empty.

This happens often.

Transmission fluid looks good. Oil is clear. I’d say they had added a couple of quarts of oil too much. Hard to tell, because it was sucked out with a big plastic pump without gradations & it was hard to gauge the amount visually. (Until now, I never really thought much about the need to check the oil level after an oil change. Too trusting.)

Excellent advice from mcparadise about the mistaken drain plugs. While working for Subaru I saw a number of damaged and sometimes totally destroyed transmissions due to this error. This mistake is not a rare one at all.

You reference transmission fluid (automatic?) but what you should inspect is the final drive oil.