GMC 2007 Acadia Owner's Manual page 417

1. To remove the panel that covers the radiator
cap, detach fasteners and lift off panel.
2. Remove the radiator pressure cap when the
cooling system, including the upper radiator
hose, is no longer hot. Turn the pressure cap
slowly counterclockwise about one full turn.
If you hear a hiss, wait for that to stop. A hiss
means there is still some pressure left.
4. Fill the radiator with the proper DEX-COOL
coolant mixture, up to the base of the filler
neck. See Engine Coolant on page 406
for more information about the proper coolant
mixture.
3. Keep turning the
pressure cap slowly,
and remove it.
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