Originally Posted By: thunderfog
Originally Posted By: sicko
Aren't the turbo direct injection engines still fairly new to Subaru, or at least to the WRX's? With a new'ish engine it's difficult to say what oil is proven to work for it, but in the past thicker oils like GC, and Rotella T6 5w-40 have shown to be good in turbo Subarus.
If it were my vehicle, and if it didn't violate the warranty, I'd use something like Castrol 0w-40. It's actually a very thin 40, and I believe it would protect the engine and turbo just fine. If a 40 weight isn't allowed, then I'd go with something like GC, PP 5w-30, or M1 0w-30. Any one of them should offer ample protection for a 4k mile OCI.
IIRC, the 2015 WRX has the new 2.0L, while the STI uses the legacy (not the car) 2.5L engine. Someone correct me if I'm wrong.
I misread the Subaru website, you're absolutely right the WRX has the direct injection engine, but the STI still uses the port injection engine.