2004 Buick Rainier Owner's Manual - Page 316

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 do not have to add extra inhibitors or additives which claim to improve the system. These can be harmful. Adding Coolant If you need more coolant, add the proper DEX-COOL® coolant mixture at the coolant recovery tank. Checking Coolant The engine coolant recovery tank is in the engine compartment on the passenger's side of the vehicle. See Engine Compartment Overview on page 5-14 for more information on location. {CAUTION: Turning the radiator pressure cap when the engine and radiator are hot can allow steam and scalding liquids to blow out and burn you badly. With the coolant recovery tank, you will almost never have to add coolant at the radiator. Never turn the radiator pressure cap - even a little - when the engine and radiator are hot. The vehicle must be on a level surface. When your engine is cold, the coolant level should be at FULL COLD, or a little higher. 5-28