Buick 2000 Century Owner's Manual page 225

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.) If you hear a hiss, wait for that to stop.
A hiss means there is still some pressure left.
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.
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.
2. Then keep turning the
pressure cap, but now
push down as you
turn it. Remove the
pressure cap.
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