1996 Pontiac Bonneville Owner's Manual - Page 269

NOTICE: If you use an improper coolant mix, your engine could overheat and be badly damaged. The repair cost wouldn't be covered by your warranty. Too much water in the mix 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. Checking Coolant NOTICE: If YOU use the propercoolant, you don't have to add extra inhibitors or additives which claim to improve .the system. These can be harmful. When your engine cold, the coolant level should be is at FULL COLD or a little higher. When your engine is warm, the level should up toFULL HOT or a be little higher.