Lets talk oil.

Your bearings do. lol

Maybe, but far as i know its always been 15w-40 rotella T in it all times of the year. At 300k and no probs yet soooo they must not notice too much lol

If you are pluggin the old diesel in, no problem, or if it doesnt get too cold...( too cold is 40 to 60 below 0 farenhieght) They handle the 15W40 fairly well....... I know that about January all of the Pickups that have diesels get a 10W40 Synthetic oil up to the mine.... The big equipment runs 20 hours a day, and is plugged in for the other 4 hours it is shut off

Last winter I tried a 5W-40 in the Duramax and it seemed to like it a lot better then the 15W-40. Definately going to do that again this winter.

A 5w40 huh? Is that a synthetic? I would think so, as I havent ever seen anything that is a dinosaur oil that was lower than a 10w40

Yes sir. Rotella T Synthetic only comes in 5W-40. Their convential oil is a 15W-40, which stinks, because if they made a synthetic 15W-40, I would buy that instead...

Last winter I used Mobil 1 5W-40 and I know Amsoil makes a 5W-40 as well.