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Viscous Fan Clutch Not Working and Troubleshoot Guide

This guide will go through the reason why your fan clutch may be faulty and how to diagnose step-by-step

Engine fan consume the largest portion of the energy supply from the engine, up to 10%

Fan clutch functions includes:

  • Reduce fan energy consumption
  • Reduce friction and noise
  • Regulate engine temperature
  • Reduce dirt and impurities
  • Saves fuel
viscous fan clutch structure

How viscous fan clutch works

  • When the engine is in low temperature or in capacity, the clutch is separated, fan speed rotates at low speed
  • When the engine is at high capacity and the water temperature rises, the clutch coupled and rotate together, the fan rotates at high speed
  • When water temperate reach designated low temperature, the clutch reverts back to separated state
  • The ECU will detect temperature via water temp sensor and operate accordingly

Common viscous fan clutch issues

Damaged Fan

Possible Cause: Damaged engine fan usually caused by friction, wear or entry of foreign objects.

Suggestion: Normally it has nothing to do with clutch fan. Seek the source of issue elsewhere

Oil Leak/Fluid Leak

Possible Cause: The outer part or solenoid coil has signs of fluid leaking. Normally it's caused by faulty clutch fan

Suggestion: Try swapping clutch fan

Damaged wire

Possible Cause: Clutch fan wire got cut/pulled by foreign factors

Suggestion: Clutch fan isn't the source of the issue.

Solenoid coil / Actuator unable to rotate

Possible Cause: Try rotating the bottom part (solenoid coil / actuator) with hand. If you have difficulty rotating or it's just stuck, then it could be either foreign object or clutch fan

Suggestion: See if there's any foreign object stuck on clutch fan, if any foreign objects absent, then it is likely the clutch fan. 


engine belt stuck on clutch fan

Engine belt stuck on clutch fan, causing solenoid coil/actuator unable to rotate

Troubleshooting steps

1. Engine fan check - See if any damages on fan

2. Clutch fan check - See if any visible damage on clutch fan

3. Wire check - See if the wire to ECU is normal

4. Solenoid coil / Actuator check - Try rotating solenoid coil / actuator and see if it's stuck

5. Check with diagnostic tool scanner - See if the readings reach the desired levels

6. Solenoid coil / Actuator testor - Test solenoid coil / Actuator if you have an actuator tester. Normal solenoid coil electric current should be 40mA to 60mA


Viscous fan clutch is going to be the norm when more industrial engine uses ECM/ECU. It relies on temp sensor to detect temperature and send signals through ECM/ECU and switches the clutch fan to different levels accordingly. It will regulate engine temperatures more efficiently compared to older direct fuel injection engine models.

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