Hey guys,

Need help please, looked all over online and can't seem to find the answer to my issue.

Here is a little background.

2006 Dodge Ram 2500 Hemi

water pump was leaking....replaced.....along with fan clutch and thermostat

Fan is running (and loud) for about 3-6 mins when accelerating....never happened before..

after driving for a bit or letting it sit and idle it will stop and everything sounds fine....

Any help will be appreciated, thank you.

 

Its takes a while for the fluid inside the fan clutch to warm and disengage the clutch.

 

At what speeds does it happen? If it's anything under 35mph or so it is operating just fine in my opinion...

I'd have to read up on the Fan to know for sure, but usually they disengage once you get over a certain speed and the IAT is low enough....

If you have a scan-tool that can read out info, let us know what the Intake Air Temperature (IAT) is when this happens and just before and after it happens too.

 

FAN DRIVE VISCOUS


DESCRIPTION

GAS ENGINES



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.


DR/DH ENGINE 7 - 69



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 viscous

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 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.


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.


7 - 70 ENGINE DR/DH



DIAGNOSIS AND TESTING

VISCOUS FAN DRIVE


NOISE

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



² The underhood temperature is above the engagement point for the viscous drive coupling. This may occur



when ambient (outside air temperature) is very high.


² Engine loads and temperatures are high such as when towing a trailer.

² 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 thermometer)


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

² 3.7L Automatic - 93° C - 99°C (200° F - 210° F)

² 3.7L Manual/4.7L Automatic/5.9L - 85° - 91° C (185° - 195° F)

² 4.7L Manual - 74° - 79° C (165° - 175° F)

² 5.7L

² 5.9L

² 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:


² 3.7L Automatic - 76°C - 81°C (168° F - 178° F)

² 3.7L Manual/4.7L Auto/ 5.9L - 67°C - 73°C (153° F - 163° F)

² 4.7L Manual - 56°C - 62°C (133° F - 143° F)

² 5.7L


DR/DH ENGINE 7 - 71

² 5.9L

² 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:



² Fan duty cycle high. This may occur when ambient (outside air temperature) is very high.

² Engine loads and temperatures are high such as when towing a trailer.

² Operating conditions where transmission temperatures may be high

² 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.

 

I think that's normal, my truck does the same thing especially when it hasn't warmed up