Cooling Fan Comes on When Car is Cold – Causes and Fixes 

Cooling Fan Comes on When Car is Cold

The cooling fan is one of the significant internal components of a vehicle. But it can act up from time to time, leaving you to wonder why. Have you ever needed clarification about why cooling fan comes on when car is cold? 

It can be concerning when it does come on under such an instance when it is not supposed to act that way. 

We have presented a detailed disclosure of why the cooling fan of your automobile unnecessarily functions out of the blue and how you can resolve the issue actively. 

You will also get a proper comprehension of how the cooling fan functions in your vehicle, eventually letting you understand the issues better and fix them efficiently. 

How does the Cooling Fan Work? 

The cooling fan does not constantly function upon starting your car. 

The primary function of the cooling fan is to cool down the engine body when the temperature exceeds the optimal range. 

The engine might heat up when the car is moving at a slow pace or idling for a considerable time. 

The optimal temperature the car engine can reach is 200 degrees Fahrenheit. The cooling fan will kick off the action when the machine goes beyond this level. 

The radiator fins of the cooling fan will pull in cool air and distribute it within to bring down the engine’s temperature and ensure safe and better overall performance. 

Why Cooling Fan Comes on When Car is Cold? 

Notice sometimes your cooling fan will stay on even when the car is cold. It can be concerning since it is unusual. What causes this to happen?

Well, there are a few possible reasons for this issue in your car. Let us analyze the causes one by one as we go down. 

  • Defective Cooling System Thermostat 

The cooling system thermostat in your car ensures the engine is functioning within the safe and average temperature range. If the thermostat is stuck closed, it won’t be able to perform its function and maintain the engine temperature. 

The engine will be easily overheated without a cooling system thermostat’s involvement. This can cause the cooling fan to come on even when the engine is cold. (Especially if the air conditioning is left on) 

  • Fault in Coolant Temperature Sensor 

Sensors are one of the primary devices when it comes to controlling the temperature levels in your car. Without sensors, we wouldn’t know the temperature level to take the respective actions. 

Basically, sensors function by monitoring the engine functionalities and temperature levels. 

It automatically updates the ECU when functions/ temperature exceeds the standard limit. 

If the engine is overheated, the sensor will signal the cooling fan upon detecting the issue. And the cooling fan will come on to bring the problem down and return the engine functionalities to normal condition. 

But suppose these coolant temperature sensors are damaged or faulty. In that case, they will send misleading information to the ECU and cause glitches in operation.

This can cause the cooling fan to come on even when the car is cold. 

  • Activation of Defrost Function 

If the defrost feature is enabled in the vehicle, it will most likely make the cooling fan come on. This can serve as another likely reason. 

  • A Glitch in the Thermostatic Switch 

Suppose you accidentally leave the thermostatic switch unplugged. In that case, it can cause the cooling fan to come on to prevent overheating in the engine. 

Sometimes a plugged thermostatic switch can also give rise to such a problem if any faults are found in the wiring (i.e., damaged or loosened wires)  

  • A Glitch in the ECU/ ECM 

An ECU (electronic control unit) or ECM (electronic control module) is a computer system that monitors your vehicle’s sensors and controls the devices’ functioning. 

A signal from ECM/ ECU will trigger the target device and make them operate. Suppose an issue is present in this computer system. In that case, normal functioning will be affected, and it will start to function abnormally. 

The devices relying on the ECU/ ECM signals may be misled by the misleading and incorrect Signals relayed due to the prevalent issue within the system. 

Such an issue can also be the culprit of making the cooling fan come even when the car is cold. 

How to Fix Cooling Fan Coming on When Car is Cold? 

We know the likely causes of the cooling fan that comes on when it is not needed. Now let us discuss how we can resolve the issues and actively fix the car. 

Stay tuned

  • If the problem lies on a stuck closed thermostat, it is likely because of the wrong installation. Or it can assume that the thermostat is not a suitable one. A corrupted thermostat can also result in being stuck closed. To fix the problem, inspect the thermostat by removing it. If you can make it detach it (heat it in a pot of water), look for clogs and deposits, and clean it up. If you fail to do so, you should replace it with a suitable one. 
  • If it is due to damage in the sensors, there is no other option than replacing the sensors with new ones. 
  • Inspect the thermostatic switch that is found below the radiator. Ensure it is correctly plugged in. restart the system to check the functioning after plugging in the button correctly. If there are still glitches in the switch, there might be some severe damage. Replace the switch and try again. 
  • If the problem is rooted in the activated defrost function, you can get it deactivated by consulting a professional. However, you can attempt fixing the speed of the temperature and blower manually before. 
  • If you suspect the issue is from the ECM / ECU, you will have to replace it with a new system as soon as possible. Since the computing system is software coded, they can be invaded by malware which can cause them to function abnormally. Using an ECM/ ECU with an abnormal operation is highly unsafe. 


A cooling fan in a car can come on even when the engine is cold due to many possible causes. Identifying and fixing the issue will resolve the problem and ensure seamless performance. 

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