GMC 1993 Safari Owner's Manual page 267

Radiator Pressure Cap
PO407
Your radiator pressure cap is a 15 psi (105 kPa) pressure-type
m n ._
must be tightly installed to prevent coolant
loss
and possible eng ...-
damage from overheating. Be sure the arrows on the pressure cap h e
UD
with overflow tube on the radiator filler neck.
When you replace your radiator pressure cap, an AC@ cap is recommended.
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.
6-29