GMC SIERRA 1995 Manual page 246

NOTICE:
In cold weather, water can freeze and crack the engine, radiator,
heater core and other parts. So use the recommended coolant.
A
CAUTION:
You
can be burned if you spill coolant on hot engine parts.
Coolant contains ethylene glycol and it will burn if the engine
parts are hot enough. Don't spill coolant on a hot engine.
1. You can remove the coolant surge tank pressure cap when the cooling
system, including the coolant surge tank pressure cap and upper
radiator hose, is no longer hot. Turn the pressure cap slowly to the left
until it first stops. (Don't press down while turning the pressure cap.)
If you hear a hiss, wait for
that
to stop.
A hiss
means there
is still some
pressure left.
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