I ran a 15w40 diesel oil in my 235 , though there is some debate on here about using a diesel oil . You can still get a oil additive from GM dealers to bump the zinc level up or at least you could a couple of years ago.

Last edited by Hydra1/2ton; 07/15/2013 10:28 PM.
First time I saw this truck I said "That's the one!"
1954 Canadian-built Chev Short Box