Buick 2002 Regal Owner's Manual page 234

How to Add Coolant to the Radiator
NOTICE:
Your engine has a specific radiator fill procedure.
Failure to follow this procedure could cause your
engine to overheat and be severely damaged.
Turn the pressure cap slowly counterclockwise until
it first stops. (Don't press down while turning the
pressure cap).
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.
If you hear a hiss, wait for that to stop. A hiss means
there is still some pressure left.
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