Buick 1998 Century Owner's Manual page 281

What to Use
Use a mixture of one-half clean water (preferably
distilled) and one-half DEX-COOL@ coolant which
won't damage aluminum parts. If you use this mixture,
you don't need to add anything else.
Adding only plain water to your cooling system
can be dangerous. Plain water, or some other
liquid like alcohol, can boil before the proper
coolant mixture will. Your vehicle's coolant
warning system is set for the proper coolant
mixture. With plain water o r the wrong mixture,
your engine could get too hot but you wouldn't
get the overheat warning. Your engine could
catch fire and you or others could be burned.
Use a 50/50 mixture of clean water and
DEX-COOL@ coolant.
NOTICE:
If you use an improper coolant mixture, your
engine could overheat and be badly damaged.
The repair cost wouldn't be covered by your
warranty.
Too
much water in the mixture can
freeze and crack the engine, radiator, heater core
and other parts.
If
you have to add coolant more than four times a year,
have your dealer check your cooling system.
NOTICE:
If
you use the proper coolant, you don't have to
add extra inhibitors or additives which claim to
improve the system. These can be harmful.
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