Have used it for 40 years. 400 hp Ag tractors all the way to my 13 HD Limited. All run 15w-40. 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.