The time has come to change the oil in my MazdaSpeed 6. I bought two jugs of Mobil 1 0W-30 AFE to get the $10 rebate. The car takes six quarts or so. I was thinking about grabbing a Mobil 1 oil change special from AutoZone with some 0W-40 European Formula for my car and a couple of quarts of 5W-20 for our CX-9. I'm hoping the one quart of 0W-40 might give a little boost to the 0W-30 to help with fuel dilution and the hot weather we've had in Houston. Will there be a problem? Is the one quart really going to make a difference at all?