2003 GMC Sonoma Owner's Manual - Page 298

How to Add Coolant to the Coolant Recovery Tank If you haven't found a problem yet, but the coolant level isn't at the ADD mark, add a 50/50 mixture of dears, drinkable water and DEX-COOL@ engine coolant at the coolant recovery tank. See Engine Coolant on page 5-27 for more information. Adding only plain waterto 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 wouldn't 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. 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. 5-35