Fan Clutch Tutorial
Part 1
Part 2
Part 3

Non-thermal clutches operate based on the shaft speed of the water pump. At low and idling speeds the clutch allows the fan blade to turn at almost a 1:1 ratio. At high speeds the silicone fluid contained in the clutch will lose its ability to transfer the energy from the shaft to the fan clutch body (and therefore the fan) and the fan is then allowed to almost free-wheel, removing its load from the engine.

The thermal fan clutch is a little more sophisticated and operates, as the name implies, in response to underhood temperatures. When the engine is cold, the fan is disconnected; when too much heat is generated, the fan is allowed to cool the engine. A bi-metal thermostatic coil mounted at the front of the clutch senses the underhood temperature and operates the clutch accordingly.

Electronic - Viscous EV Fan Clutch Operation
The ECM/PCM signal controls the level of engagement of the EV clutch. An internal solenoid opens a spring loaded valve which allows silicone drive fluid to flow from the storage reservoir to the working area of the unit engaging the clutch. This engagement process is ultimately controlled through the ECM/PCM by the following input variables: Coolant Temperature, Intake Manifold Temperature, Transmission Oil Temperature, A/C Pressure and Engine Oil Temperature. These variables are manufacturer specific and fan speed is dictated based on the level of cooling required. Please consult the Original Equipment specifications to determine which set of variables apply to your vehicle.

Electronic-Viscous Fan Clutch Troubleshooting
During engine start up, the EV fan clutch will engage and match engine speed for up to 3 minutes. This is considered normal and may last more than 3 minutes in cooler climates or at lower driving speeds resulting in fan roar. This condition will cease shortly upon disengagement. Additionally, you may hear an audible “clicking” sound when the vehicle is stationary. These conditions are normal and should cease once the fan clutch disengages.

  • Do NOT replace EV fan clutch unless a specific issue is identified by proper SI (Service Indicator / Check Engine) diagnosis.
  • Do NOT replace an EV fan clutch for fan noise.
  • Do NOT replace an EV fan clutch unless a specific condition related to the EV fan clutch is identified using SI diagnostics. If the EV fan clutch has a condition that warrants replacement, a DTC (Diagnostic Trouble Code) should set and/or SI diagnostics should lead to the replacement of the fan clutch.
  • Do not attempt to replace EV Fan Clutch without proper tools. Please refer to manufacturer requirements for proper tools and replacement.

Next - Fan Clutch Tutorial - Part 3

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