1996 GMC Sonoma Owner's Manual - Page 201

How to Add Coolant to the Coolant Recovery Tank If you haven't found a problem yet, but the coolant level isn't at ADD, add a SO/SO mixture of clecr/z cr.nter(preferably distilled) and DEX-COOL (orange-colored, silicate-free) antifreeze at the coolant recovery tank. (See "Engine Coolant" in the Index for more information.) TM 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. 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's coolant warning mix. With system is set for the proper coolant plain water or the wrong your engine could mix, get too hot but you wouldn't get the overheat warning. Your engine could catch fire and or you others could be burned. Use a 50/50 mix of clean water and DEX-COOL antifreeze. TM 5-15