my 02 hit 50k, and i went to mobil full syn 5w-40. Since i have been in the oil/ fuel additive business i have learned alot. just did a power service class even. people think backwards on oil, as i used to. us stroker users with the oil fed injectors, this full syn makes a difference! At initial start up, it is a 5w oil but since it is a full synthetic, all the lubrication properties are greater than a 15w oil. But at full temp the 40w is the same. makes start ups easier and easier on your equipment. Faster oil pressure build (especially in cold weather), and the protection of a full synthetic oil. believe it or not...delo is one of the low grade oils now.