Buick 1994 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.
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.)
Add coolant mix at the recovery tank, but be careful not
to spill
it.
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