[peterbilt]

imported post

i use valvoline 10w40 and put some seafoam in about 100 miles before each service flushes nice and easy i have friends that run 20 50 oil, they take alittle longer to warm up and get rollin normally plus i wouldnt run anything over 10w40 anyway its a fluid cooled so you dont have to have the oil so thick if your engine is original and older you could blow it up with the thicker oils