Here's a few things I got from the FAQ's on Blackstone's site. As far as type of oil used by Blackstone employee's. They say the mostly use mineral oil because it does what they need it to do. When it comes to when to change oil, as far as age or mileage goes, they feel just having old oil in a vehicle doesn't harm anything. Oil usage gives the best indication of the condition of a motor. I liked their analogy of, using Synthetic oil will not guarantee longer engine life, like eating a vegetarian diet will not guarantee you longer life.,,,