Hummer 2007 H3 Owner's Manual page 344

3. Fill the radiator with the proper DEX-COOL
coolant mixture, up to the base of the filler
neck. See Engine Coolant on page 335
for more information about the proper coolant
mixture.
4. Fill the coolant recovery tank to the
FULL COLD mark.
5. Reinstall the cap on the coolant recovery tank,
but leave the radiator pressure cap off.
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6. Start the engine and let it run until you can
feel the upper radiator hose getting hot.
Watch out for the engine cooling fan.
7. By this time, the coolant level inside the
radiator filler neck might be lower. If the level is
lower, add more of the proper DEX-COOL
coolant mixture through the filler neck until the
level reaches the base of the filler neck.
8. Then replace the pressure cap.
At any time during this procedure if coolant begins
to flow out of the filler neck, reinstall the pressure
cap. Be sure to secure it tightly.
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