Modern oil in antique cars
My service manual says to use 20-weight oil in my 1938 Buick. Can I use 10W-30 oil safely or is there a better choice? The car is rarely driven.
Buick recommended single viscosity 20-weight non-detergent oil back in 1938 because that was what was available. Since those days motor oil has undergone an evolution that has made it much more effective than anything available in the pre-war era. Modern multi-viscosity oil will be just fine in your Buick, and the detergents in modern oils will not cause a problem in your classic’s engine because it is not aggressive enough to break away chunks of sludge, as some old-timers might say. Instead it will just slowly clean your engine.
The one thing I would recommend to optimize engine wear though, is to use oil especially intended for classic cars or add a ZDDP zinc additive for maximum protection. Today’s engine oils don’t contain zinc oxide because it clogs catalytic converters, but modern cars use roller lifters to compensate for the lack of that lubricant and protectant that was added to motor oil in the old days. You can use modern oil but I would add a ZDDP additive available at auto parts stores.