In California? Yeah 10w-40 all year round should be fine. When it gets below freezing is when you may want to back it off to 5w-40 perhaps. Originally these engines called only for *w-40 oil. The manual stated that *w-30 oils were only to be run in the absence of available *w-40, and only for a short time at that. Since then there are now some 5w-30 oils that meet VW spec. But I prefer the 5w-40 myself, especially on a 1.8T with high miles.