Pontiac G5 Owner's Manual page 295

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. Do not 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 counterclockwise
about two or two and one-half turns. If you
hear a hiss, wait for that to stop. This will let
any pressure still left to be vented out the
discharge hose.
2. Then keep turning
the pressure
cap slowly, and
remove it.
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