I've got a 2008 Mazda3. I live in Houston where it's been around 100º everyday. It won't start cooling off till mid October. My car has only had 5w-20, mostly Pennzoil Platinum. I've had good UOAs. Last oil change was done at the dealer because it was too hot for me do it. This dealer features Quaker State products. I guess they put 5w20 QS according to the window sticker. My question is would there be any advantage to running a 5w-30 during this hellacious Texas summer? or should I just continue 5w-20 year round? The car runs just fine, has 36,000 miles and I the A/C is usually on full blast anytime I'm in the car.