1998 Pontiac Bonneville Owner's Manual - Page 275

What to Use Use amixture of one-half clean water (preferably distilled) and one-half DEX-COOL@coolant which won't damage aluminum parts. If you use this mixture, you don't need to add anything else. NOTICE: If you usean improper coolant mixture, your engine couldoverheat 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 fourtimes a year, have your dealer check your cooling system. Adding only plain water to your cooling system can be dangerous. Plain water, or some other the liquid like alcohol, can boil before proper coolant mixture will. Your vehicle's coolant warning systemis set for the proper coolant mixture. With plainwater or the wrong mixture, your engine could get too but you wouldn't hot get the overheat warning. Your engine could catch fire and you or others could beburned. Use a 50/50 mixture of clean water and DEX-COOL@coolant. I NOTICE: If you use the proper coolant, you don't have to add extrainhibitors or additives which claim to improve the system. Thesecan be harmful. 6-24