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Subaru oil change 5 qt vs 4.2 qt

I have a 2004 Subaru Outback which has 63,000 miles on it and has always been serviced at the Dealership where it was purchased. At my last visit I was told the engine head gasket has a small leak and there was too much oil. Apparently the mechanic at the dealership has been adding 5 qt oil instead of the 4.2 qt stated in the owners manual. Is this a problem? Could this have caused the headgasket problem?

While he should not have been doing this, if it were high enough to cause damage you’d have experienced engine-destroying bearing knock long ago. You can sleep soundly.

The only reason overfilling is bad is because if the level gets too high the crankshaft can whip the oil into a froth, and that hinders the sbility of the lubrication system to do its job. The oil pump is two interlocked impellars, designed to pump oil in the manner of a hydraulic pump. Air bubbles simply compress and impair the ability of the pump to maintain pressure. And any frothed oil that would get to the bearings would not be able to maintain the pressurized fluid barrier between the surfaces that unfoamed oil does.

No, that would have had no influence on the headgasket leak whatsoever. That’s a whole seperate problem.

So, too much oil does not result in headgasket leakage. Thank you, the same mountainbike, for answering my question.

You’re very welcome.