Hummer 2006 H3 - Manual (Page 298)

Adding Coolant
If you need more coolant, add the proper DEX-COOL ®
coolant mixture at the coolant recovery tank.
{ CAUTION:
Turning the radiator pressure cap when the
engine and radiator are hot can allow steam
and scalding liquids to blow out and burn
you badly. With the coolant recovery tank,
you will almost never have to add coolant at
the radiator. Never turn the radiator pressure
cap — even a little — when the engine and
radiator are hot.
Add coolant mixture at the recovery tank, but be careful
not to spill it.
{ CAUTION:
You can be burned if you spill coolant on hot
engine parts. Coolant contains ethylene glycol,
and it will burn if the engine parts are hot
enough. Do not spill coolant on a hot engine.
Occasionally check the coolant level in the radiator.
For information on how to add coolant to the radiator,
see Cooling System on page 5-29.
5-26