1995 Buick Park Avenue Owner's Manual - Page 204

How to Add Coolant to the Radiator . ,A ' j ' " ' . I 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 to the left until it first stops. (Don't press down while turning the pressure cap.) 3. Fill the radiator with the proper mix, up to the base of the filler neck. If you hear a hiss, wait for that to stop. A hiss means there is still some pressure left. 5-16