1993 Buick Century Owner's Manual - Page 204

When the coolant inthe coolant recoverytank is at or above the "FULL HOT" mark,start your vehicle. If the overheat w r i g continues, there's one more thing you ann can t y You can add the proper coolant mix directlyo r. t the radiator, but be sure the cooling system is cool before you do it. /i\ CAUTION: Steam andscalding liquids from a hot cooling system can blow out and burn you badly. They are under pressure, andif you turn theradiator pllessure cap--even a little-they can -me out at hlgh speed. NeAler turn the cap when the cwllng q t r , Including the radiator sen pressure cap, is hot. Wait tor the cooling system and radiator pressure to c o o l if you cap ever have to turn the pressure cap. I 202