Tommy,
What year and size engine are you referring to?
GM recommended multi-viscosity oils for 1954 and later 235/261 engines (and also recommended single weight oils).
These would be fine:
10W-30
10W-40
15W-30
15W-40
and even 20W-50 would do no harm to a 1954 and later 235/261 engine
Diesel oil with ZDDP would be fine.
