Checking For A Defective Fan Clutch

First, let’s discuss what the fan clutch does and why it is there. It is a mechanism on engines with belt-driven cooling fans that will clutch the fan on and off depending on the need for more or less cooling air to flow through the radiator. When cruising at highway speeds in a moderate climate, the fan should be idling along turning just fast enough to add a little air flow when needed. At low speeds, the fan clutch will sense higher temperatures through the radiator and “clutch up” thereby increasing the fan speed to maintain constant engine temperature.



If you think that your fan clutch is defective and not working properly, listed here are some recommended procedures to check the condition of the fan clutch:

1. Start the engine with the hood open and note if the fan is turning. Now increase the engine RPM and check if the fan speed and noise increases. If it does, then it’s fine. But if the speed/noise doesn’t increase, then the clutch needs replacement.

2. If it’s working, then leave the engine running in idle and note after 2-5 minutes if the fan speed/noise slows down or not. While raising the RPM, the fan then should not make much noise as it did earlier. If the fan slows, it’s fine. But if speed/noise does not decrease then it’s a sign of “frozen clutch” and hence needs replacement.

3. Leave the engine idle and also watch the temperature indicator in the dashboard. If the fan speed/noise increases in normal temperature when RPM is increased, it’s a good sign. But if the temperature indication continues to increase with no increase in fan speed/noise, then the fan clutch should be replaced.

4. After the engine is at normal operating temperature or above, take some newspaper and roll it up into a long narrow tube. Be very careful not to keep your hands and fingers near to the fan while performing this test. When the engine is idle and has reached operating temperature, insert the rolled paper on the back of the fan pushing it towards the centre hub of the fan while avoiding the blades. If the fan cannot be stopped then it’s good but, if it can be stopped the clutch is defective and should be replaced.

5. Similarly, you can also check the fan clutch by spinning it when the engine is off. A good clutch should offer a certain amount of resistance when spun by hand. If the fan spins easily (more than 1 to 2 turns), the fan clutch needs replacement. If it binds, does not turn or offers more resistance, then the fan clutch is seized and needs to be replaced.

6. Try wiggling the fan blades by hand when the engine is off. If there is any wobble then there is a bad bearing in the fan clutch, or a worn bearing on the water pump shaft. If there’s a worn bearing on the water pump shaft causing it to leak and/or make noise, the clutch should be replaced. A bad water pump bearing will usually cause the water pump to leak and/or make noise, but not always.

7. Defective fan clutch causes problem in the vehicle’s air conditioning system too. The reason is because the fan cools the air conditioners sensor which is in front of the radiator.


Testing can be performed in any order but just make sure the conditions during testing are those that are specified for that specific test. Do not continue to operate the engine if the temperature continues to rise and certainly stop if the temperature approaches “redline”. It’s better if you can detect a fan clutch problem and leave the replacing to a professional mechanic. Just remember that a common symptom of the clutch fan failure is the car overheating when idling…


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Mr. Kalash Ratna Tuladhar is a graduate from the Minnesota State University in Automotive Engineering Technology. He formerly worked for MV Agusta and Bikers Nepal as the Head of after sales. Currently he is planning to open his own workshop “Iron Monk Moto” at Gairidhara, Kathmandu. It may seem that an oil change is a […]

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