2005 Pontiac GTO Owner's Manual - Page 217

How to Add Coolant to the Coolant Overflow Reservoir {CAUTION: Adding only plain water to your cooling system can be dangerous. Plain water, or some other liquid such as alcohol, can boil before the proper coolant mixture will. Your vehicle's coolant warning system is set for the proper coolant mixture. With plain water or the wrong mixture, your engine could get too hot but you would not get the overheat warning. Your engine could catch fire and you or others could be burned. Use a 50/50 mixture of clean, drinkable water and DEX-COOL® coolant. If you have not found a problem yet, check the coolant level on the coolant overflow reservoir dipstick. If the coolant level is not at or above the bottom arrow on the dipstick, add a 50/50 mixture of clean, drinkable water and DEX-COOL® coolant at the coolant overflow reservoir. See Engine Coolant on page 5-23 for more information. Notice: In cold weather, water can freeze and crack the engine, radiator, heater core and other parts. Use the recommended coolant and the proper coolant mixture. {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. 5-31