GMC 1996 Sierra Owner's Manual page 280

Radiator Pressure Cap
(Gasoline Engine)
The radiator pressure cap must be tightly installed with
the arrows
on
the cap lined LIP with the overflow tube on
the radiator filler neck.
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.
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