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 used oil analysis. 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 5w30 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.