Hummer 2006 H3 - Manual (Page 301)

Cooling System
When you decide it is safe to lift the hood, here is what
you will see:
A. Coolant Recovery Tank
B. Engine Cooling Fan
C. Radiator Pressure Cap
If the coolant inside the coolant recovery tank is
boiling, do not do anything else until it cools down.
The vehicle should be parked on a level surface.
When the engine is cold, the coolant level should
be at least up to the FULL COLD mark. If it is not,
you may have a leak at the pressure cap or in
the radiator hoses, heater hoses, radiator, water
pump or somewhere else in the cooling system.
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