Chevrolet 2003 Monte Carlo Owner's Manual page 271

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.
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.
The radiator pressure cap is located in the front of the
engine compartment on the passenger's side of the
vehicle, near the diagonal cross brace. See Engine
Compartment Overview on page 5-12 for more
information on location.
2. Then keep turning the pressure cap, but now push
down as you turn it. Remove the pressure cap.
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