1994 Buick Century Owner's Manual - Page 227

To Check Coolant When your engine is cold, the coolant level should be at "ADD" or a little higher. When your engine is warm, the level should be up to "FULL HOT'' or a little higher. Add coolant mix at the recovery tank, but be careful not to spill it. To Add Coolant If you need more coolant,add the proper mix at the coolant recovery tank. If the coolant recovery tank is completely empty, add coolant to the radiator. (See "Engine Overheating"in the Index.) 225