GMC 1995 Safari Owner's Manual page 232

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.
Thermostat
Engine coolant temperature is controlled by a thermostat in the engine
coolant system. The thermostat stops the flow of coolant through the
radiator until the coolant reaches a preset temperature.
When you replace your thermostat, an AC@ thermostat is recommended.