How To Add Coolant To The Radiator - GMC 2006 Envoy Owner's Manual

If the overheat warning continues, there is one more
thing you can try. You can add the proper coolant
mixture directly to the radiator, but be sure the cooling
system is cool before you do it.
CAUTION:
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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 radiator
pressure cap — even a little — they can come
out at high speed. Never turn the cap when the
cooling system, including the radiator pressure
cap, is hot. Wait for the cooling system and
radiator pressure cap to cool if you ever have
to turn the pressure cap.

How to Add Coolant to the Radiator

1. You can remove the radiator pressure cap when
the cooling system, including the radiator pressure
cap and upper radiator hose, is no longer hot.
Turn the pressure cap slowly counterclockwise about
one full turn. If you hear a hiss, wait for that to stop. A
hiss means there is still some pressure left.
2. Then keep turning the pressure cap. Remove the
pressure cap.
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