Have used it for 40 years. 400 hp Ag tractors all the way to my 13 HD Limited. All run 15w40. My wife's 08 Ford Edge has 202,000 miles on it and still doesn't use any oil in 6,000 mile oil changes. I have never seen the need for syn oil. I have more engines on this farm than most people will own in their lifetime and have not lost one yet.