I have a 2005 Subaru Legacy with the 2.5 normally aspirated engine. I have 135,000 miles. I change oil every 5000 with synthetic, and have been since I bought it 4 years/35,000 miles ago.
I would not normally consider an engine flush (I’m using synthetics, changing oil at under the synthetic recommendation), but the engine has developed a noise on start-up. It sounds like a possible rod knock/collapsed lifter on the #1 cylinder. When the car is cold, the noise goes away once the engine reaches about 2000-2500 rpm. Once the car is warmed up, the engine noise also goes away at idle.
I’ve tried a little Marvel Mystery Oil in the crankcase, and that seemed to help quiet it down somewhat.
My guess (without tearing the engine apart) is that there is a restricted oil passage to one of the bearings. I’d rather try a cheap fix than an engine rebuild/change for this older car.
Yes, I know the manual says not to do an engine flush. The manual ALSO doesn’t talk about the known head gasket problems with this car, or the requirement to replace the coolant every year to keep the passenger-side heater from growing scale enough to keep that heater from working. It also doesn’t tell me why the headlights keep popping every 3 months.
Does anyone have any recommendations on which engine flush to use?