Thanks for all the good information. My engine was rebuilt a couple years ago and only has around 500 miles on it. Should I still use 15w40 during the winter months or would a 10w30 be better? Is there a huge difference?
You're in Southern California. No need to change weights at all. I'd wager $100 that you've rarely seen below freezing. If you were in Alaska, then maybe, but I run 15W-40 in my diesel year round up here.
[on edit] Went back and saw that you're in Missouri now (you should change your profile location.) You'll still be fine with 15W40 year round. It might occaisionally get colder there than in SouthCentral Alaska, but still OK.
