Buick 1994 Century Owner's Manual page 226

Adding Coolant
NOTICE:
If you use an improper coolant mix, your engine
could overheat and be badly damaged. The
repair cost wouldn't be covered by your
warranty. Too much water in the mix can freeze
and crack the engine, radiator, heater core and
other parts.
The coolant recovery tank is located on the passenger's
side of the engine compartment.
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