I decided I'm going to try a 40 weight oil in my Mustang once the Auto-Rx rinse cycle is done and I'm wondering which M1 variety everyone thinks would be the best. Choices - Delvac 1/Truck and SUV 5W-40 0W-40 Mix equal parts 5W-30 and 15W-50 The car sits almost all winter and never gets driven when it's below about 40 degrees. It gets used for trips and an occasional autocross in the summer. The reasons for wanting to use M1 are the easy availability and cost. It gets changed often enough vs. the mileage that how it works for any extended drain isn't an issue. Opinions please !