Dodge RAM TRUCK 1500 1995 Service Manual page 318

7 - 48 COOLING SYSTEM SERVICE PROCEDURES
B R
(5) Remove fan Hade-to-viscous fan drive mount­
ing bolts.
Inspect the fan for cracks, loose rivets, loose or
bent fan blades.
INSPECTION
The fan cannot be repaired. If the fan is damaged,
it must be replaced. Inspect the fan as follows:
(1) Remove fan blade and thermal viscous fan
drive assembly from engine. Refer to the preceding
Removal procedure.
(2) Remove fan blade assembly from thermal vis­
cous fan drive unit (four bolts).
(3) Lay fan on a flat surface with leading edge fac­
ing down. With tip of blade touching flat surface, re­
place fan if clearance between opposite blade and
surface is greater than 2.0 mm (.090 inch). Rocking
motion of opposite blades should not exceed 2.0 mm
(.090 inch). Test all blades in this manner.
WARNING: DO NOT ATTEMPT TO B E N D
OR
STRAIGHTEN FAN B L A D E S IF NOT WITHIN S P E C I ­
FICATIONS.
(4) Inspect fan assembly for cracks, bends, loose
rivets or broken welds. Replace fan if any damage is
found.
CAUTION: If the fan blade assembly is replaced be­
cause of mechanical damage, the fan pulley and
viscous fan drive should also be inspected. These
components could have been damaged due to ex­
cessive vibration.
INSTALLATION'
(1) Install fan blade assembly to viscous fan drive.
Tighten mounting bolts to 23 N-m (17 ft. lbs.) torque.
(2) Position the fan shroud and fan blade/viscous
fan drive to the vehicle as an assembly.
(3) Install viscous fan drive assembly on fan hub
shaft. Tighten mounting nut to 57 N-m (42 ft. lbs.)
torque.
(4) Install fan shroud bolts.
(5) Install battery cables to batteries.
VISCOUS FAN DRIVE
OESCilPTIOl AID 0PERATI0I
Also refer to either of the previous Cooling System
Fan sections.
The thermal viscous fan drive (Figs. 68 or 69) 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.
A thermostatic bimetallic spring coil is located on
the front face of the viscous fan drive unit (a typical
viscous unit is shown in figure 70). 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 re­
gardless of engine speed.
MOUNTING NUT
TO WATER PUMP
Fig. 70 Viscous Fan Drive—Typical
Only when sufficient heat is present, will the vis­
cous fan drive engage. This is when the air flowing
through the radiator core causes a reaction to the bi­
metallic 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 re­
acts and the fan speed is reduced to the previous dis­
engaged speed.
CAUTION: Some engines equipped with serpentine
drive belts have reverse rotating fans and viscous
fan drives. They are marked with the word R E ­
V E R S E to designate their usage. Installation of the
wrong fan or viscous fan drive can result in engine
overheating.
CAUTION: If the viscous fan drive is replaced be­
cause of mechanical damage, the cooling fan
blades should also be inspected. Inspect for fatigue
cracks, loose blades, or loose rivets that could
have resulted from excessive vibration. Replace fan
blade assembly if any of these conditions are
found. Also inspect water pump bearing and shaft
assembly for any related damage due to a viscous
fan drive malfunction.