[Werner]

Gasoline engine oils from API SC upwards contain additives that attack non-ferrous metals (bearing bronze) and white metals in the plain bearing shells of the crankshaft and connecting rod. Therefore it is better to use API SC.

This has nothing in common with the viscosity!



But the large tolerances of old engines always need a relatively thick oil. Multigrade oil is good. But not with too low base viscosity! Every oil - even multi-range! - becomes thinner with increasing temperature. A multigrade oil only becomes "slower" thinner. Therefore, 10W-XX is less favorable for these engines than 20W-XX.

I worked as a consultant in the lubricants industry and have my own mix: SAE 25W-50 in class API SC.