Pontiac 1997 Grand Prix Owner's Manual page 254

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.
hose, is no longer hot. 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 pressureleft.
2. Then keep turning the pressure cap, but now push
down as you turn it. Remove the pressure cap.
1. You can remove the pressure cap when the cooling
system, including the pressure cap and upper radiator
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