Just had a quick question. I don't own one, but the Subaru WRX (Turbo engine)looks pretty quick for a Subaru. Just courious could an oil like Castrol GTX 10w30 handle the demands of a Subaru Turbo engine?
The owners manual lists 5W30 (preferred), 10W30, and 10W40, IIRC. I'd recommend Mobil1 0W40 for the WRX turbo from what I see posted on this board.
As far as Castrol goes, I wouldn't recommend any but the European formulations, not GTX.
There aren't too many non synthetic oils which can handle the heat of a turbo unfortunately. Although I got decent life out of a Chrysler turbo engine running Castrol XLR 10w30 (Canadian's will remember this oil from the 80s)