Bobtheoilguy is a very interesting read. Grandpa always said 10w30 in the winter and 10w40 in the summer, sounds like he may have been wrong. Bob seems to indicate that the first number is the one you want to switch with the seasons. I've always believed that additives are not good with the exception of slick 50 in tired old engines. I've seen it written recently that the only people who promote additives are those who stand to make money off of them. I don't have any stock in slick 50, just good experience with using it.
