1993 Buick Century Owner's Manual - Page 205

How to Add Coolant to the Radiator d ' 1. You can remove the I 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 to the left until it first stops. (Don't press down while turning the pressure cap.) If you hear ahiss, wait for that to stop.A hiss means there is still some pressure left. F 3. Fill the radiator with the proper mix, up to the base of the filler neck. I 4. Then ffl the coolant recovery tank to the "FULL HOT" mark. 2. Then keep turning the pressure cap,but now push down as youturn it. Remove the pressure cap. I !1 I J A = 203