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Why Radiator Fan Goes ON and OFF?


Why Radiator Fan Goes ON and OFF?

Your car’s radiator fan plays a crucial role in its proper functioning. It ensures your car’s components don’t suffer damage from overheating. So when it suddenly turns on and off, it’s natural to feel concerned.

A radiator fan goes on and off to maintain optimum temperatures. They turn on to cool your car and off once the temperature is at the lowest possible level. However, a radiator fan may also turn on and off to signal that there’s something wrong with your vehicle.

This article will explain the purpose of a radiator and how it functions. I’ll also discuss why your car’s radiator fans go on and off under normal circumstances. Finally, I’ll help you determine whether your radiator fan going on and off is a sign you should troubleshoot your car. 

How Does a Car Radiator Work?

Your car can move around thanks to its internal combustion engine. When the internal combustion engine runs, it generates energy, which creates heat. The car radiator ensures that the heat produced by your car’s engine doesn’t reach dangerous levels. 

A car radiator keeps your engine from overheating. It uses the principle of convection to transfer heat away from the engine towards the surrounding atmosphere. The radiator uses a complex system of thermostats, coolants, and fans to work.

By itself, an increase in your car’s temperature is not a cause for concern. However, beyond certain thresholds, high temperatures can damage the internal components of your vehicle. This is where your car’s radiator comes in.  

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The Car Generates Heat When It Starts

Before I explain how your car’s radiator works, you must understand how your car generates heat. As you know, an internal combustion engine keeps your vehicle going.

If you check your internal combustion engine, you’ll see it has a cylinder with a moving piston inside. The engine pushes combustion gasses into the cylinder, which moves the piston, which in turn drives the complex gear system that powers your car. This process generates large amounts of energy, and when there’s enough energy in one place, that place heats up.   

Typically, your car engine’s temperature should fall between 195 and 220 degrees Fahrenheit (91 to 104 degrees Celsius). When the engine exceeds that temperature, your thermostat triggers the radiator fan.  

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The Radiator Releases Liquid Coolant and Water That Absorb Heat

When your radiator activates, it releases liquid coolant and water. If you’re worried about liquid getting into your engine, the coolant and water have a crucial function. Both absorb the excess heat from your engine before returning to the radiator. 

The Radiator Transfers the Heat Away From the Car Engine

Once the heated coolant and water return to the radiator, your radiator’s fan blows into them to cool them down. The heat transfers to the air outside the vehicle through this process, keeping the heat away from the engine. 

The Radiator Turns Off When the Job Is Done

At this point, your engine’s temperature should drop below a defined threshold, and the heat from the coolant should completely dissipate into the atmosphere. The radiator fan will then switch off, and the radiator will stop pumping coolant. If the engine’s temperature goes above a critical level again, the cycle above will repeat. 

How Do You Know if the Car Radiator Fan Is Working Properly?

In most cases, a car radiator fan going on and off isn’t a cause for concern. If anything, it’s usually a sign that the radiator is doing its job. Otherwise, your car will overheat without your knowledge and will be worse off for it.

You’ll know if the car radiator fan is working properly if there are no other signs of damage. For example, if you don’t see smoke coming out from underneath the hood or the engine temperature gauge doesn’t hit “high,” it’s safe to say your car radiator fan is okay.

On the other hand, your radiator fan may turn on and off to signal something wrong with your car. How do you know if that’s the case? In the next section, I’ll discuss the signs your car radiator isn’t working correctly. 

Read: Temperature Gauge High But Car Is Not Overheating

What Are the Signs a Car Radiator Isn’t Working Properly?

There are instances when your car radiator turning on and off is a sign that something’s wrong with your car. It’s important to recognize these signs, as the proper procedure to fix your radiator will depend on what’s wrong with the vehicle. 

Here are signs a car radiator isn’t working properly: 

  • The radiator fan doesn’t turn on despite high temperatures.
  • The radiator fan won’t switch off and stays permanently on.
  • Your car’s engine is constantly overheating.
  • The coolant is leaking or not pumping.

Below, I’ll talk about why these are signs that your car radiator isn’t working properly. I’ll also touch on other reasons you’re experiencing these issues and how to resolve them (if you don’t need professional help). 

The Radiator Fan Doesn’t Turn On Despite High Temperatures

If the temperature gauge shows that your engine is overheating, but your radiator fan does not kick in, it could mean your radiator is not functioning effectively. However, it’s essential to note that the radiator fan or motor may not be the problem. 

As noted, the radiator fan depends on several critical components to execute its functions properly. For the radiator fan to spin at the appropriate temperatures, other parts such as thermostats and fan switches must be in proper working condition. 

Therefore, a fan switch or thermostat failure can also keep your radiator fan from kicking in. If you’re experiencing this problem, do a step-by-step troubleshoot before you go out and buy any parts for your vehicle.   

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The Radiator Fan Won’t Switch Off and Stays Permanently On

A permanently switched-on radiator fan is as problematic as a fan that will not turn on. It can signal that your radiator is not cooling your car’s engine as intended. Similar to the issue discussed above, the failure of other components may play a role in why this problem exists.

For example, the radiator’s water or coolant may require replacement. Alternatively, the pump that pushes coolant and water around the engine may have failed. It’s also possible that the feed hose attached to the pump is damaged or leaking. If the fan stays on long after the engine has shut down or after it has cooled down, the thermostat or fan switch is most likely to blame. 

I suggest you isolate the faulty component before looking for replacement parts or a new radiator. Check the quality of the coolant or water. Inspect the coolant pump or feed hose to see whether those are the source of your problems.

Read: What Happens If The Car Engine Coolant Is Low?

Your Car’s Engine Is Constantly Overheating

If your car’s temperature gauge consistently displays temperatures above 220 degrees Fahrenheit (104 degrees Celsius) over prolonged periods, your radiator has probably failed. In this case, it may no longer be safe to drive your vehicle, and you should address this issue as soon as possible.

The Coolant Is Leaking or Not Pumping

Another common symptom of radiator failure is leaking or improperly circulating coolant. The most likely cause of coolant leakage is a damaged feed hose. On the other hand, if you find that the coolant isn’t pumping through the feed hose, the radiator pump has probably failed.

If you’re not sure about the exact cause of a malfunctioning radiator, it’s best to consult an expert to determine the source of the problem. If you’re comfortable fixing your car yourself without professional help, that works too. If you are fixing your vehicle yourself, be sure to do a thorough troubleshoot to determine the source of the problem before you purchase any replacement parts.


Radiators play a critical role in maintaining the temperatures of car engines within an optimum range. They’re essential to the proper maintenance and functioning of these machines. If there’s anything wrong with your radiator, troubleshoot it as soon as you can.

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