1998 Buick Regal Owner's Manual - Page 289

NOTICE: If you use an improper coolant mixture, your engine could overheat and be badly damaged. The repair cost wouldn't be covered your by 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. Checking Coolant - NOTICE: If you usethe proper coolant, you don't have to 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 the COLD mark or a little higher. When your engine is warm, the level should be up to the HOT mark or a little higher. 6-25