1999 Buick Riviera Owner's Manual - Page 218
1999 Buick Riviera Manual
Page 218 highlights
yellowblue 5. Put the cap back on the coolant recovery tank, but leave the radiator pressure cap off. 7. By this time, the coolant level inside the radiator filler neck may be lower. If the level is lower, add more of the proper DEX-COOLR coolant mixture through the filler neck until the level reaches the base of the filler neck. 8. Then replace the pressure cap. At any time during this procedure if coolant begins to flow out of the filler neck, reinstall the pressure cap. Be sure the arrows on the pressure cap line up like this. 6. Start the engine and let it run until you can feel the upper radiator hose getting hot. Watch out for the engine cooling fans. 5-16