I bought a 2007 Ford Mustang the otherday with 44,000 miles. Questioning the seller he stated he did his own oil changes. The car is a V6 and Ford calls for 5w30 oil. The seller said he runs 10-30 in the winter and 10-40 in the summer. Never 5-30 as he thought it was to light.I live in the desert part of my state and summers get to the 90's for a few momnths and winter some times 17 above zero, but usually in the 30's. This car will not be run in the winter except on occasion at 40 plus degrees outside. I think just 10-30 all year should be fine as it has never run on 5-30. Thinking of using Mobil 1 as that is what I use in my other vehicles. Any thought and opinions are welcome. Thanks,Spad