After the engine has been running for thirty to forty minutes it idles rough and high MPG

ROSI

MEMBER
2009 SUBARU TRIBECA
3.5L
6 CYL
109,500 MILES

After replacing all four oxygen sensors and MAF sensor problem still persist. Subaru dealership told me that the engine has low compression in 140-150 PSI range in all six cylinders and I need to replace engine. The car runs just fine. I do not understand how is this possible. I am devastated. Please advise.

1 Reply

STEVE W.

MECHANIC
13,449 POSTS

Well those numbers are a bit low, that engine should be in the 180-220 psi range. However, it sounds more like it may simply need to have the head gaskets replaced, Subaru engines all seem to have gasket failures. I would do a leak down test to see if the engine is leaking past the rings or valves first. This lists a few tests that can be done, by you or most shops (you do not have to use a dealer) to see if this could be the problem. Then see what the pricing would be for the repair. Shop around a bit if you do not want to DIY the repairs.

https://www.2carpros.com/articles/head-gasket-blown-test