1997 GMC Sonoma Owner's Manual - Page 214

How to Add Coolant to the Coolant R I rovery Tank 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 mix. -A CAUT'3N: 5-16 IT you haven't found a problem yet, but the coolant level isn't at ADD, add a 50/50 mixture of clean water (preferably distilled) and DEX-COOL@ (silicate-free) antifreeze at the coolant recovery tank. (See "Engine Coolant" in the Index for more information.) I I Adding only plain water to your cooling system can be dangerous. Plain water, or some other liquid like alcohol, can boil before the proper coolant mix will. Your vehicle'scoolant warning system is set for the proper coolant With mix. plain water or the wrong your engine could mix, you get too hot but wouldn't get the overheat warning. Your engine could catch fire and or you others could be burned. a 50/50 mix of clean Use water andDEX-COOL' coolant.