2003 Buick Century Owner's Manual - Page 240

Adding only plail. .later to your cooling system can be dangerous. Plainwater, or some other liquid such as 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 50/50mixture of clean, drinkable water and DiiX-C00Ls cooiant. Notice: If you use an improper coolant mixture, your engine could overheat and be badly damaged. The repair cost 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 than four times a year, have your dealer check your cooling system. Notice: If you use the proper coolant, you don't have to add extra inhibitors or additives which claim to improve the system. These can be harmful. 5-23