Chevrolet 2007 HH7 Owner's Manual page 314

If no coolant is visible in the coolant recovery tank,
add coolant at the pressure cap as follows:
CAUTION:
{
Steam and scalding liquids from a hot
cooling system can blow out and burn
you badly. They are under pressure, and if
you turn the pressure cap — even a
little — they can come out at high speed.
Never turn the cap when the cooling
system, including the pressure cap, is hot.
Wait for the cooling system and pressure
cap to cool if you ever have to turn the
pressure cap.
314
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
®
coolant.