My 1992 f-250, I changed the oil and at 2300 miles it was kind of dirty. I kept joking that I've added so much oil that it should have been cleaner. Maybe the Marvel mystery one-quart oil top off did its job in the fifty miles it was used. I put in SuperTech 5-30 high mileage full synthetic. and a Motorcraft Fl-1A filter. I changed the oil when I first got the truck and it has sat a lot since then, The rear main seal used to leak and mark its spot and now it doesn't. I'm not sure what Maricle has happened but now I have to figure out why my truck uses oil. It doesn't smoke or leave spots on the ground. I bought my oil online from Wall Mart, two jugs and a filter were enough for free shipping.