Originally Posted by bluesubie
5W-30 is not recommended by the factory. It is listed as the preferred weight by SoA for fuel economy and the OP's owner's manual states thicker viscosities are recommended for severe conditions and in higher temps. Although FHI does have to approve SoA's recommendations. By recommending 5W-30, SoA is saying that it's fine to run an oil with an operating viscosity of a 20 weight. Make one modification to your engine's performance and you should toss the oil weight recommendations out the window (unless you've chosen viscosity based on oil pressure readings).
It's funny that someone could probably post here asking if running 5W-20 in a WRX was ok and people would think they were nuts. Fact is, a Resource Conserving oil will shear to a 20 weight very quickly so there really isn't any difference since 5W-20's are very stable.
would you recommend a 5w40 or 50. Im using redline oil and its a 2005 wrx.