What is the factory recommended oil for a 1981 Chevy Silverado 350 CID engine?
The factory recommendation for a 1981 Chevy Silverado 350 CID engine's oil would depend on the specific climate where the truck was operated and the owner's manual. However, in general, for that era and engine, it would likely have specified a SAE 10W-30 or 20W-40 oil, likely a conventional oil (not synthetic). The owner's manual would detail the exact specification, including the API service classification (like SG or SH; these would be older classifications). Checking the owner's manual is crucial for definitive information.