i guess i cant see how the oil would make any differnce unless your running regual oil and its thick because it's cold out. it comes w/ synthetic stock so i guess ill stay w/ stock oil. for the price we payed for this wheeler whats a few more bucks for the right oil. its not like it takes alot to change it. as far as the milage goes, it all depends on your right thumb doesn't it. lol.