1999 Chevrolet Astro Owner's Manual - Page 224

yellowblue If there seems to be no leak, start the engine again. See if the engine cooling fan speed increases when idle speed is doubled by pushing the accelerator pedal down. If it doesn't, your vehicle needs service. Turn off the engine. CAUTION: 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 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-COOLR coolant. 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 clean, drinkable water and DEX-COOLR engine coolant at the coolant recovery tank. (See "Engine Coolant" in the Index for more information.) 5-12