Buick 1994 Century Owner's Manual page 190

NOTICE:
In cold weather, water can freeze and crack the
engine, radiator, heater core and other parts. Use
the recommended coolant.
When the coolant in the coolant recovery tank is at or
above the the "FULL HOT" mark, start your vehicle.
If the overheat warning continues, there's one more
thing you can try. You can add the proper coolant mix
directly to the radiator, but be sure the cooling system is
cool before you do it.
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