Hi- Just got back from the Ford dealer today after geting some warranty work done, and I had a chance to talk with a Factory Technician. He stated that Cam. shaft differences in the newer mustangs require 5W20 to lubricate efficiently at higher RPMs. This is the first time that I have actually met an individual who has stated a direct change in the 4.6L modular motor that supports the newer oil. Can I count on Red Line 5W20 to protect as well as a 5W30 or 10W30 in the lower RPM range? What's the deal? I have mechanics telling me that it is important to stick with 5W20. Others are saying that the only reason for the lighter oil is CAFE concerns. I switched to Red Line 5W20 today,, down from Red Line 5W30.