Hummer 2006 H3 - Manual (Page 305)

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 may 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.
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.
Engine Fan Noise
This vehicle has a clutched engine cooling fan.
When the clutch is engaged, the fan spins faster to
provide more air to cool the engine. In most everyday
driving conditions, the clutch is not engaged. This
improves fuel economy and reduces fan noise.
Under heavy vehicle loading, trailer towing and/or high
outside temperatures, the fan speed increases when
the clutch engages. So you may hear an increase in
fan noise. This is normal and should not be mistaken
as the transmission slipping or making extra shifts.
It is merely the cooling system functioning properly.
The fan will slow down when additional cooling is not
required and the clutch disengages.
You may also hear this fan noise when you start the
engine. It will go away as the fan clutch disengages.
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