2006 Pontiac Grand Prix Owner's Manual - Page 340

If the overheat warning continues, there is one more thing you can try. You can add the proper coolant mixture directly to the radiator, but be sure the system is cool before you do it. {CAUTION: Steam and scalding liquids from a hot cooling system can blow out and burn you badly. They are under pressure, and if you turn the pressure cap - even a little - they can come out at high speed. Never turn the cap when the cooling system, including the pressure cap, is hot. Wait for the cooling system and pressure cap to cool if you ever have to turn the pressure cap. 3800 V6 Supercharged Engine shown, 3800 V6 Engine similar 1. You can remove the pressure cap when the cooling system, including the pressure cap and upper radiator hose, is no longer hot. Turn the cap slowly counterclockwise. 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 and remove it. How to Add Coolant to the Radiator (3800 V6 Engines) Notice: Your engine has a specific radiator fill procedure. Failure to follow this procedure could cause your engine to overheat and be severely damaged. 5-34