GMC 1997 Safari Owner's Manual page 285

Radiator Pressure Cap
NOTICE:
Your radiator cap is a 15 psi (105 kPa)
pressure-type cap and must be tightly installed
to prevent coolant loss and possible engine
damage from overheating. Be sure the arrows on
the cap line up with the overflow tube on the
radiator filler neck.
When you replace your radiator pressure cap, a GM cap
is recommended.