Hummer 2006 H2 - Manual (Page 359)

Cooling System
When you decide it is safe to lift the hood, here is what
you will see:
A. Coolant Surge Tank
B. Coolant Surge Tank Pressure Cap
C. Engine Cooling Fan
If the coolant inside the coolant surge tank is boiling, do
not do anything else until it cools down. The vehicle
should be parked on a level surface. Check the coolant
level after the system cools down. Some amount of
coolant may be lost due to overheating.
The coolant level should be at or above 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.
{ CAUTION:
Heater and radiator hoses, and other engine
parts, can be very hot. Do not touch them. If
you do, you can be burned.
Do not run the engine if there is a leak. If you
run the engine, it could lose all coolant. That
could cause an engine fire, and you could be
burned. Get any leak fixed before you drive the
vehicle.
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