I'd been putting 10w-30 into my engine for the past 25 years. The engine is a 400ci SBC from a mid-70s GM truck. Not clear if it ever been rebuilt, as there were no records when I bought the car. I suspect not - it was more likely picked from a junkyard, hosed down, and painted to match the car.

I read a recent magazine article by somebody resurrecting an older hot rod (a barn find). Part of the process was draining the oil and filling the engine with 20w-50. Have I been doing this wrong? Are the older engines designed for the heavier weight oil? The oil pressure has always been low, in the 30-35psi range.

Thanks for help and opinions.

Dorsey