GMC 1996 Sonoma Owner's Manual page 247

A 50/50 mixture of water and the proper coolant for
your vehicle will:
0
Give freezing protection down to -34°F (-37°C).
Give boiling protection up to 265 "F
(
129°C).
Protect against rust and corrosion.
Help keep the proper engine temperature.
Let the warning lights and gages work as they
should.
NOTICE:
When adding coolant it is important that you use
DEX-COOL
TM
(orange-colored, silicate-free)
coolant meeting
GM Specification 6277M.
If silicated coolant is added to the system,
premature engine, heater core or radiator
corrosion may result. In addition, the engine
coolant will require change sooner
--
at
30,000 miles (50 000 km) or 24 months whichever
occurs first.
Use a mixture of one-half clear? ~vuter (preferably
distilled) and one-half DEX-COOL
TM
(orange-colored,
silicate-free) antifreeze that meets GM Specification
6277M, which won't damage aluminum parts. Use
GM Engine Coolant Supplement (sealer) (GM Part
No. 3634621) with any complete coolant change. If you
use this
mixture, you don't need to add anything else.
.
A dding 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 a 50/50 mix of clean
water and DEX-COOL
TM
(orange-colored,
silicate-free) antifreeze.