1994 Chevrolet Astro Owner's Manual - Page 198
1994 Chevrolet Astro Manual
Page 198 highlights
How to Add Coolant to the Coolant Recovery Tank If you haven't found a problem yet, but the coolant level isn't above at or the FULL mark, add a 50/50 mixture of clean water (preferably distilled) and a proper antifreeze at the coolant recovery tank. (See "Engine Coolant" in the Indexfor more information about the proper coolant mix.) ... I NOTICE: In cold weather, water can freeze and crack the engine, radiator, heater core and other parts. Use the recommended coolant. When the coolant in the coolant recovery tank is at above the FULL, or mark, start your vehicle. you If the overheat warning continues, there's one more thing can try. You can add the proper coolant mix directly to the radiator, but besure the cooling system is cool before youdo it.