GMC 1993 Safari Owner's Manual page 251

.
c
PO344
SAE 5W-30
As shown in this chart, SAE 5W-30 is best for your vehicle, However,
you can use SAE IOW-30 if it's going to be 0°F (-18°C) or above.
These numbers on an oil container show its viscosity, or thickness. Do
not use other viscosity oils such as SAE 1OW-40. or SAE 2OW-50.
6-1 3