5w-20 year round. It's what the dealer has for "normal" oil. My TCH is garaged and temps in San Diego rarely get below 40F. This morning was cold, 43F. Last week the lows were in the 50s.

I'm sure 0w-20 would get a tiny bit better gas mileage, and possibly get to the valve train a bit faster. I may try it once to see if I can tell any difference. Has anyone compared the two oils (5w-20 vs 0w-20) to see if their summer MPG changes enough to notice?