I understand that BMW required oil change every 25000km, but I prefer doing it every 3000 but with other oil like mobie 1, they are syp. oil, but will it harm my engine. Another question is that if the factory suggested, for example 15w oil, if I use 20w, is that ok? sorry I have driven my car for 4 years but never got a perfect anwser for these questions. Please give me a hand. Thank You!