MT3288 - 9/24/2023 20:35 Thank you for looking, So I recently had my tractor (4250 Diesel) worked on by a very good mechanic.... but there was one thing that kind of caught me off guard.... he asked what oil I was using and I said I am using Full Synthetic 5w-40... he told me to not use full synthetic nor John Deere Plus 50-II because they don't have the special ingredients to properly lubricate these older engines (I wish I remember what the "Ingredients" were that these oils are missing)..... He said to only use regular 15w-40 oil (Rotella) to properly lubricate these older diesel engines and to change the oil every 100 hours..... I wanted to see what other people, who knows a lot about these older John Deere engines, thinks about what he said and what you guys use for engine oil.... Thanks a ton!!!