I've got a crate 360 magnum in my 1991 dodge power ram 150 it's carburated and has around 20 thousand miles on it. I live in Idaho where it gets 30 below zero routinely through out winter and in the summer it can get up to 105 but is normally 85 to 100. is 5w-30 or 5w-40 better for this engine in this climate?