Well, as soon as I get back from Mexico, I'm gonna change out the oil in the Lumina and put in some 15w-40, most likely some Delo 400. Anyways, I'm curious as to who on here also is running 15w-40 in a vehicle whose specs. don't call for that grade. What vehicle to you run it in? What was the manufacturers requirements (5w-30, 10w-30, etc...)? Why did you make the change? Thanks, Justin.