Chevrolet 2002 Camaro Owner's Manual page 226

How to Add Coolant to the Radiator
(3800 V6 Engine Only)
NOTICE:
Your engine has a specific radiator fill procedure.
Failure to follow this procedure could cause your
engine to overheat and be severely damaged.
5-16
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
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.