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 concernbut 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.