2004 Chevrolet Impala Owner's Manual - Page 299

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. 2. Then keep turning the pressure cap, but now push down as you turn it. Remove the pressure cap. The radiator pressure cap is located in the front of the engine compartment near the diagonal cross brace on the passenger's side of the vehicle. See Engine Compartment Overview on page 5-12 1. 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. {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. Do not spill coolant on a hot engine. 5-37