1998 Chevrolet Astro Owner's Manual - Page 289

NOTICE: If you use an impropercoolant mixture, your engine could overheat and be badly damaged. The repaircost wouldn't be covered by your warranty. Too much water in the mixture can freeze and crack the engine, radiator, heater core and other parts. If you have to add coolant more thanfour times a year, have your dealer check your cooling system. Checking Coolant .. I NOTICE: If you use the proper coolant, don't have to you add extra inhibitors or additives which claim to improve the system. These can be harmful. When your engine is cold, the coolant level should be at ADD, or a little higher. When your engine is warm, the level should be up to FULL HOT, or a little higher. 6-27