Buick 2007 Rainier Owner's Manual page 388

How to Add Coolant to the Radiator
1. You can remove the radiator pressure cap
when the cooling system, including the
radiator pressure cap and 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.
2. Then keep turning the pressure cap. Remove
the pressure cap.
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3. Fill the radiator with the proper DEX-COOL
coolant mixture, up to the base of the filler
neck. See Engine Coolant on page 379
for more information about the proper coolant
mixture.
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