1999 Buick Riviera Owner's Manual - Page 217

yellowblue How to Add Coolant to the Radiator 1. You can remove the radiator pressure cap when the cooling system, including the radiator pressure cap and upper radiator hose, is no longer hot. Turn the pressure cap slowly counterclockwise until it first stops. (Don't press down while turning the pressure cap.) If you hear a hiss, wait for that to stop. A hiss means there is still some pressure left. 2. Then keep turning the pressure cap, but now push down as you turn it. Remove the pressure cap. 3. Fill the radiator with the proper DEX-COOLR coolant mixture, up to the base of the filler neck. (See "Engine Coolant" in the Index for more information about the proper coolant mixture.) 4. Then fill the coolant recovery tank to FULL COLD. 5-15