2003 Chevrolet 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. 5-36