From Castrol's website:
is a premium, super multigrade that provides maximum protection in all seasons and can help extend engine life. SAE 10W-40 exceeds API service SM, SL, SJ and SH as well as exceeding the engine protection requirements for API Certified Gasoline Engine Oils.
Castrol SAE 10W-40:The guy up top put in Castrol 10W40, about which I expressed some concern but he assured me that between the heat and the old engines wear it would be better for it. Well so far that seems to be holding true. I expected it to sound like a threshing machine but it actually sounded better than when I got there. I learned later that the oil, because of the fact that the engine doesn't have roller lifters, should be an SL type. Well I couldn't get an answer one way or the other about that so this morning I picked up a zinc additive to add to the oil.
is a premium, super multigrade that provides maximum protection in all seasons and can help extend engine life. SAE 10W-40 exceeds API service SM, SL, SJ and SH as well as exceeding the engine protection requirements for API Certified Gasoline Engine Oils.