2004 Buick Park Avenue Owner's Manual - Page 278

How to Add Coolant to the Radiator 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. Do not 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. 2. Then keep turning the pressure cap, but now push down as you turn it. Remove the pressure cap. 3. Remove the 3800 Series II V6 engine cover shield to access the bleed valve. 5-34