Dodge Ram Truck 1500-2500-3500. Manual — part 241

5.9L DIESEL ENGINE

The electronically controlled viscous fan drive is
attached to the fan drive pulley mounted to the
engine. The coupling allows the fan to be driven in a
normal manner. The fan speed is controlled by the
electronic control module.

OPERATION

GAS ENGINES

A thermostatic bimetallic spring coil is located on the
front face of the viscous fan drive unit (a typical vis-
cous unit is shown in. 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.

Only when sufficient heat is present, will the viscous
fan drive 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 neces-
sary 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.

5.9L DIESEL

The Engine Control Module (ECM) controls the level of engagement of the electronically controlled viscous fan
clutch by monitoring coolant temperature, intake manifold temperature, air conditioning pressure and transmission oil
temperature. Based on cooling requirements, the ECM sends a signal to the viscous fan clutch to increase or
decrease the fan speed.

Fan speed is monitored by the ECM. Fan speeds above or below a calibrated threshold will set a DTC. Circuit
concerns will also set fan clutch DTC’s.

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DIAGNOSIS AND TESTING

VISCOUS FAN DRIVE

NOISE

NOTE: It is normal for fan noise to be louder (roaring) when:

•

The underhood temperature is above the engagement point for the viscous drive coupling. This may occur
when ambient (outside air temperature) is very high.

•

Engine loads and temperatures are high such as when towing a trailer.

•

Cool silicone fluid within the fan drive unit is being redistributed back to its normal disengaged (warm) position.
This can occur during the first 15 seconds to one minute after engine start-up on a cold engine.

LEAKS

Viscous fan drive operation is not affected by small oil stains near the drive bearing. If leakage appears excessive,
replace the fan drive unit.

VISCOUS DRIVE

If the fan assembly free-wheels without drag (the fan blades will revolve more than five turns when spun by hand),
replace the fan drive. This spin test must be performed when the engine is cool.

For the following test, the cooling system must be in good condition. It also will ensure against excessively high
coolant temperature.

WARNING: BE SURE THAT THERE IS ADEQUATE FAN BLADE CLEARANCE BEFORE DRILLING.

1. Drill a 3.18-mm (1/8-in) diameter hole in the top center of the fan shroud.

2. Obtain a dial thermometer with an 8 inch stem (or equivalent). It should have a range of -18°-to-105°C (0°-to-

220° F). Insert thermometer through the hole in the shroud. Be sure that there is adequate clearance from the
fan blades.

3. Connect a tachometer and an engine ignition timing light. The timing light is to be used as a strobe light. This

step cannot be used on the diesel engine.

4. Block the air flow through the radiator. Secure a sheet of plastic in front of the radiator. Use tape at the top to

secure the plastic and be sure that the air flow is blocked.

5. Be sure that the air conditioner (if equipped) and blowe fan is turned off.

WARNING: USE EXTREME CAUTION WHEN THE ENGINE IS OPERATING. DO NOT STAND IN A DIRECT LINE
WITH THE FAN. DO NOT PUT YOUR HANDS NEAR THE PULLEYS, BELTS OR FAN. DO NOT WEAR LOOSE
CLOTHING.

6. Start the engine and operate at 2400 rpm. Within ten minutes the air temperature (indicated on the dial ther-

mometer) should be up to 88° C (190° F). Fan drive engagement should start to occur at/between:

•

3.7L Automatic - 93° C - 99°C (200° F - 210° F)

•

3.7L Manual/4.7L Automatic/5.9L - 85° - 91° C (185° - 195° F)

•

4.7L Manual - 74° - 79° C (165° - 175° F)

•

5.7L

•

5.9L

•

Engagement is distinguishable by a definite increase in fan flow noise (roaring). The timing light also will

indicate an increase in the speed of the fan.

7. When viscous drive engagement is verified, remove the plastic sheet. Fan drive disengagement should start to

occur at or between:

•

3.7L Automatic - 76°C - 81°C (168° F - 178° F)

•

3.7L Manual/4.7L Auto/ 5.9L - 67°C - 73°C (153° F - 163° F)

•

4.7L Manual - 56°C - 62°C (133° F - 143° F)

•

5.7L

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•

5.9L

•

8.3L engine - 93° to 101° C (190° - 205° F) Minimum 73°C (163°F). A definite decrease of fan flow noise
(roaring) should be noticed. If not, replace the defective viscous fan drive unit.

CAUTION: Some engines equipped with serpentine 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 overheating.

CAUTION: If the viscous fan drive is replaced because 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.

ELECTRONICALLY CONTROLLED VISCOUS FAN DRIVE

NOISE

NOTE: It is normal for fan noise to be louder (roaring) when:

•

Fan duty cycle high. This may occur when ambient (outside air temperature) is very high.

•

Engine loads and temperatures are high such as when towing a trailer.

•

Operating conditions where transmission temperatures may be high

•

Cool silicone fluid within the fan drive unit is being redistributed back to its normal disengaged (warm) position.
This can occur during the first 15 seconds to one minute after engine start-up on a cold engine.

LEAKS

Viscous fan drive operation is not affected by small oil stains near the drive bearing. If leakage appears excessive,
replace the fan drive unit.

ELECTRONICALLY CONTROLLED VISCOUS DRIVE – 5.9L DIESEL

If the fan assembly free-wheels without drag (the fan
blades will revolve more than five turns when spun by
hand), do not replace the fan drive. This spin test
must be performed when the engine is cool.

If the fan assembly does not free-wheel and a metallic
grinding sound exists, replace the electronically con-
trolled fan drive (Refer to 7 - COOLING/ENGINE/RA-
DIATOR FAN - REMOVAL).

NOTE: The following test may take up to 15 min-
utes to perform.

The engine should be at normal operating tempera-
ture.

1.

Set the parking brake and verify the transmission

is in park or neutral.

2. Set air conditioner (if equipped) and blower fan to

OFF.

3. Start and allow engine to reach normal operating

temperatures.

4. Stop engine, connect the scan tool and select

appropriate model year and engine option.

5. Check for and correct existing DTC’s

6. Using Tool 6801, connect pin 1 of the electronically controlled viscous fan drive connector, located at the lower

fan shroud to battery ground.

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7. Using the scan tool, verify that DTC 0480 set.

8. Start the engine.

9. Go to the SENSOR screen and observe the fan speed.

10. Run the engine at 2500 rpm.

NOTE: It maybe take 15 minutes before fan speed increases.

11. The fan speed should increase according to the table below.

12. If fan speed does not increase, replace the electronically control viscous fan drive.

ELECTRONICALLY CONTROLLED VISCOUS FAN DRIVE SPEEDS

ENGINE RPM

FAN RPM (Min)

500

490

1000

950

1500

1420

2000

1850

2500

2230

3000

2440

13. If the fan speed does increase and there is still a concern, refer to the appropriate Engine Electrical Diagnosis

Section to diagnosis the electronically controlled viscous fan drive control circuit.

CAUTION: If the viscous fan drive is replaced because of mechanical damage, the cooling fan blades
should also be inspected. Inspect for fatigue cracks or chips that could result in excessive vibration.
Replace fan blade assembly if any of these conditions are found.

REMOVAL

3.7L/4.7L/5.7L ENGINE

1. Do Not attempt to remove the fan/viscous fan drive

assembly from the vehicle at this time.

CAUTION: If the viscous fan drive is replaced
because 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 condi-
tions are found. Also inspect water pump bearing
and shaft assembly for any related damage due to
a viscous fan drive malfunction.

2. Disconnect negative battery cable from battery.

3. Remove coolant reserve/overflow container from

fan shroud and lay aside. Do Not disconnect the
hoses or drain coolant from the container.

4. Using Special Tool 6958, remove the fan blade/vis-

cous fan drive assembly from the water pump by
turning the mounting nut counterclockwise as
viewed from the front. Threads on the viscous fan
drive are RIGHT-HAND..

5. Do Not unbolt the fan blade assembly from viscous fan drive at this time.

6. Remove the fan shroud-to-radiator mounting bolts.

7. Pull the lower shroud mounts out of the radiator tank clips.

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