Hummer 2004 H2 - Manual (Page 349)

5. With the coolant surge tank pressure cap off, start
the engine and let it run until you can feel the upper
radiator hose getting hot. Watch out for the
engine cooling fan.
By this time, the coolant level inside the coolant
surge tank may be lower. If the level is lower, add
more of the proper mixture to the coolant surge tank
until the level reaches FULL COLD mark.
6. Then replace the pressure cap. Be sure the
pressure cap is hand-tight and fully seated.
Engine Fan Noise
Your 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 fan is spinning
slower and the clutch is not fully engaged. This
improves fuel economy and reduces fan noise. Under
heavy vehicle loading, trailer towing and/or high outside
temperatures, the fan speed increases as the clutch
more fully 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 partially
disengages.
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