N14 Base Engine Troubleshooting and Repair Manual – 008-028   Fan Clutch, Viscous

Use a fan RPM measuring device to check the operation of the viscous fan hub. A strobe or Cummins optical tachometer, Part No. 3377462, can be used.

Mark a spot on the fan hub pulley and on one fan blade so the measuring device can determine the pulley and the fan speed. Reflective tape, Part No. 3377464, in Cummins optical tachometer, Part No. 3377462, can be used to mark the fan blade and the pulley. (Refer to Service Tools Instruction, Bulletin No.

3377544, for more information.)

While the engine is still warm and the vehicle is shut off, cover the radiator grill.

Leave a hole approximately 0.3 m [1-foot] in diameter in the cardboard to allow some air flow to the viscous fan hub.

Start the engine. Idle the engine for 3 to 5 minutes. Lock the throttle in a “HIGH IDLE” position.

On CELECT™ engines, use the PTO option to operate the engine at maximum PTO engine RPM.

Refer to the CELECT™ System Troubleshooting and Repair Manual, Bulletin No.

3666084.

When the coolant temperature reaches 91°C [195°F], measured fan speed

must
reach a minimum of 85 percent of a pulley speed.

The measured fan speed divided by the measured fan hub (pulley) speed

must
be greater than or equal to 0.85.

 Measured Fan Speed 

 >= 0.85
Fan Hub (Pulley) Speed       

While the engine is still at high idle, remove the radiator grill cover. The fan speed

must
begin to decrease after one (1) minute and eventually drop to a maximum of 50 percent of the input pulley speed.

If the viscous fan hub fails this test, have it checked by an authorized fan hub dealer for repair or replacement.

If the fan does

not
operate within the temperature range indicated in the Thermal Control Settings Chart shown in the front of this section, the fan clutch and the controls

must
be checked. Refer to the fan clutch manufacturer’s service manual.

If a fan speed measuring device is

not
available and the complaint is overheating, remove the viscous fan hub bimetal strip and the control pin. This will cause the fan hub to operate all the time.

If the overheating complaint does

not
occur with the control pin removed, install the control pin and take the fan hub to an authorized fan hub dealer for repair or replacement.

Loosen and remove the capscrews or the hexagon nuts which hold the viscous fan clutch to the fan hub.

NOTE: Do

not
discard the fan spacers. The spacers provide the thickness needed to install the fan in the correct position.

Carefully remove the fan and clutch assembly from the fan shroud, and put it on a workbench with the pin side up.

Remove the capscrews or the hexagon nuts which hold the fan to the clutch.

NOTE: If the control pin is removed, the control pin side of the assembly

must
be up to prevent fluid loss which will result in incorrect fan clutch performance.

Install the fan on the viscous fan clutch. Install the capscrews or the hexagon nuts which hold the fan to the clutch.

Make sure the correct number of spacers are still on the fan hub.

Tighten the mounting capscrews or hexagon nuts.

Refer to the manufacturer’s recommendation for torque value.

Carefully install the fan and clutch assembly into the fan shroud.

Tighten the mounting capscrews to the vehicle manufacturer’s specifications.