GMC Denali 2004 Owner's Manual page 314

What to Use
Use a mixture of one-half clean, drinkable water and
®
one-half DEX-COOL coolant which won't damage
aluminum parts. If you use this coolant mixture,
you don't need to add anything else.
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CAUTION:
Adding only plain water to your cooling
system can be dangerous. Plain water, or
some other liquid such as 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 or the
wrong mixture, your engine could get too hot
but you would not get the overheat warning.
Your engine could catch fire and you or others
could be burned. Use a 50/50 mixture of clean,
drinkable water and DEX-COOL
5-22
®
coolant.
Notice: If you use an improper coolant mixture,
your engine could overheat and be badly damaged.
The repair cost would not 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 do not
have to add extra inhibitors or additives which claim
to improve the system. These can be harmful.