Dodge 2000 DURANGO Service Manual page 211

DN
DESCRIPTION AND OPERATION (Continued)
Fig. 16 Spring Clamp Size Location
1 – SPRING CLAMP SIZE LOCATION
The spring type hose clamp applies constant ten-
sion on a hose connection. To remove a spring type
hose clamp, only use constant tension clamp pliers
designed to compress the hose clamp.
VISCOUS FAN DRIVE
DESCRIPTION
CAUTION: Engines equipped with accessory drive
belts have reverse rotating fans and viscous fan
drives. They are marked with the word REVERSE to
designate their usage. Installation of the wrong fan
or viscous fan drive can result in engine overheat-
ing.
The thermal viscous fan drive is a silicone-fluid-
filled coupling used to connect the fan blades to the
water pump shaft. The coupling allows the fan to be
driven in a normal manner. This is done at low
engine speeds while limiting the top speed of the fan
to a predetermined maximum level at higher engine
speeds.
On all 4.7L an electrical cooling fan located in the
fan shroud aids in low speed cooling, It is designed to
augment the viscous fan, However, it does not
replace the viscous fan.
A thermostatic bimetallic spring coil is located on
the front face of the viscous fan drive unit. This
spring coil reacts to the temperature of the radiator
discharge air. It engages the viscous fan drive for
higher fan speed if the air temperature from the
radiator rises above a certain point. Until additional
engine cooling is necessary, the fan will remain at a
reduced rpm regardless of engine speed.
Fig. 17 Fan Blade/Viscous Fan Drive—4.7L/5.2L/5.9L
1 – VISCOUS FAN DRIVE
2 – FAN BLADE
3 – SCREW AND WASHER
Fig. 18 Viscous Fan Drive—4.7L/5.2L/5.9L Engines—
1 – VISCOUS FAN DRIVE
2 – THERMOSTATIC SPRING
3 – MOUNTING NUT TO WATER PUMP HUB
OPERATION
When sufficient heat is present, the viscous fan
drive will engage. This is when the air flowing
through the radiator core causes a reaction to the
bimetallic coil. It then increases fan speed to provide
the necessary additional engine cooling.
Once the engine has cooled, the radiator discharge
temperature will drop. The bimetallic coil again
reacts and the fan speed is reduced to the previous
disengaged speed.
COOLING SYSTEM
Engines
Typical
7 - 9