GMC 1993 Suburban Owner's Manual page 292

The following explains your cooling system and how to add coolant when it
is
low. If you have a problem with engine overheating, see "Engine
Overheating" in the Index.
The proper coolant for your vehicle will:
8
Give freezing protection down to
-34°F (-37°C).
e
Give boiling protection up to 258°F (125°C).
8
Protect against rust and corrosion.
Help keep the proper engine temperature.
8
Let the warning lights and gages work as they should.
What to use:
Use a mixture of clean water (preferably distilled), and antifreeze that meets
"GM Specification 6038-M," which won't damage aluminum parts. Also
use
GM Engine Coolant Supplement (sealer) with a complete coolant change. If
you ,use these, 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 mix will. Your vehicle's coolant warning system is set
for the proper coolant mix. With plain water or the wrong mix, 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
If you use an improper coolant
mix,
your engine
could
owheat 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.
Some conditions, such as air trapped in the cooling system, can affect the
coolant level in the radiator. Check the coolant level when the engine is cold
and follow the steps under "Adding Coolant" for the proper way to add
coolant.
If you have to add coolant more than four times a year, have your dealer
check your cooling system.
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