S4_Cinci (I S'edTFA)

My oil temp shows about 225 in normal driving with 0w-30 and it dropped to midway between the 200 and 225 marks when I switched to the 0w-40. Dealer put in 0w-30 at 10,000 miles and now my oil temps are back up to 225-230 again. I would be comfortable with mixing the 15w-50 and the 0w-40 at a 50/50 ratio in the summer (for midwest). I used to run 15w-50 Mobil 1 during the summer in my old domestic DOHC V8 which called for 5w-30 and put 120,000 miles on it with no oil or wear issues whatsoever. Granted; it wasn't a turbo engine so I am no expert in that respect - but I like the M1 0w-40 in the S4 over the 0w-30. Less valvetrain noise with the 0w-40 as well!

gk1

I think cars may vary since mine has always run between 200-225 with 0w-30.

Singletrack

I'd go with at least a 5w or 10w in Texas.