I mentioned in a post several weeks ago that I have a friend that was given some free M1 0w40 that he wanted to use up in his V6 2010 Toyota 4Runner. Anyway he has been running this oil and reports that his truck has never run better so his new question is can he use this oil year round? I know it is a 40 weight and his truck recommends a 30 weight but it is a 0w40 so as far as cold starting in Jan when it gets below zero will Mobil 1 0w40 flow better or worse than M1 5w30 (what he usually runs)? should he just save the rest of the 0w40 for the summer months?