A buddy of mine down here in Miami used only Mobil 1 Full Synthetic in his Screaming Eagle Ultra. From the heat, it built up a sludge in the heads and clogged up the whoel thing. Harley told him that they weren't sure if the waranty would cover it due to it not being Harley OE oil. After a fight they covered it and now he has had an overheating problem. So the bike is back in the shop. Just my info that I have for the matter.