Cars Radiator Fan Runs Constantly – Should You Be Worried?

Cars radiator fan runs constantly happens when your car’s temperature is too high. It can be due to a problem with the cooling system sensors, relay, or other parts.

cars radiator fan runs constantly

Some simple issues, such as a low amount of coolant or an unclean radiator, are easy to fix at home. Keep reading to dig deeper into all possible causes and repair actions needed to fix a radiator.

Why Does Your Car’s Radiator Fan Run Constantly?

Your car radiator fan turns constantly because of a blocked radiator or a faulty cooling system member. The cooling fan receives false signals from the temperature sensor or fan relay. Moreover, the engine overheats for various reasons, so the fan keeps moving to cool it down.

– Collapsing Coolant Temperature Sensor (CTS)

If the radiator fan keeps running when car is on, there might be a problem with the CTS. These sensors detect the change in the engine temperature and send signals to the fan.

The radiator fan works continuously when a faulty CTS sends false signals. The check engine indicator usually displays a problem in CTS, helping you detect the issue.

– Failure of the Electronic Control Unit (ECU)

ECU controls various functions of the engine. If it fails to work, the radiator keeps working. Generally, the ECU controls the fan based on the signals from the CTS.

Why Your Car’s Radiator Fan Run Constantly

This system is present in the form of a chip and works according to the commands of embedded software, but the chip would not work if it came in contact with moisture. It can happen due to water or antifreeze leakage.

– Non-functioning Cooling Fan Relay

A defective relay keeps supplying power to the regulator fans, so if the car regulator does not go off, the relay might be the culprit. Its purpose is to regulate the engine temperature by keeping the fans on or off.

But it can stop working if it wears out with time or overheats. You can detect a fault in the relay if you hear a clicking noise, especially when turning the air conditioner on.

– Loss or Leakage of Coolant

If you are wondering why is my radiator fan constantly running, a possible reason is a drop in coolant levels. The coolant brings down the temperature, so the engine takes longer to cool down if it depletes. Thus, a heated engine keeps the fan on for a long time.

The loss of coolant usually depicts a leakage either in the coolant reservoir or the thermostatic housing. These leaks can cause further damage to the car, so it is better to take the car for service.

You can check the level of coolant by opening the reservoir. The reservoir has a mark, so if the coolant lies below it, you can fill it up to the mark and fix the radiator.

– Radiator Blocked by Dirt

A dirty radiator gets heated up because the dirt blocks it, so if you are thinking why does my car’s radiator fan run constantly, there might be a blocked radiator.

You can detect a clogged radiator if the fan always starts working when you turn on the air conditioner. The dirt and debris prevent the distribution of heat around the radiator. Thus, the car’s cooling fan takes longer to cool the engine and keeps spinning.

The radiator may also be blocked because of external road dirt or internal antifreeze, but you do not have to worry — simply wash the radiator, and it will be clean again.

– Overheated Engine

If the fans are constantly running, you can have an overheated engine. Detection of engine overheating is easy as cars have a temperature indicator.

Normally, the cooling fans maintain the temperature of the regulator, but when there is a defect in a component or the coolant leaks, the engine overheats. This problem keeps the engine fan running for a long time.

– Defective Refrigerant Pressure Sensor (RPS)

If the refrigerant leaks and the RPS fails, the cooling fan stays on. The refrigerant is present in the air conditioner, so when it leaks, a warning about the overheated radiator reaches the ECU. You can diagnose this problem if the fan spins whenever you turn on the air conditioner.

– A Broken Component in the Cooling System

Sometimes the radiator stays on if there is a broken part in the engine cooling system. For instance, the wires in the radiator fan motor might break or lose insulation. You can check for signs of damaged insulation or a blown fuse.

Broken Component in Car Cooling System

Apart from that, the fan belt loosens or breaks with time. This belt rotates the fan when the ECU commands, but a loose belt keeps the fan moving. You can also check the clutch that connects the fan to the engine. Sometimes the springs inside the fan clutch show signs of wear.

How To Fix a Constantly Rotating Radiator Cooling Fan?

You can fix a constantly rotating radiator fan by cleaning it or repairing any broken part of the cooling system. This includes mending the leaks in the coolant reservoir or air conditioner. You can also restore the worn-out insulation on wires or hire a mechanic to reinstall the CTS software.

– Clean the Polluted Radiator

Cleaning a choked radiator can also fix a bad radiator fan. This will provide a better exchange of air around the radiator and cool down the engine. There might be an internal and external blockage, so for proper cleansing, you can disassemble the radiator. You may clean it yourself or bring the car to a service center.

You will see a lot of dirt and debris washed out once you wash it. But do not start the car while cleaning, and remember that you have to add the coolant afterward.

– Fix a Faulty Fan Relay

You can fix the relay if you have experience, but first you have to diagnose a defective relay. You can do that by spotting the relay and using a voltmeter to check the current. If the relay does not work, the voltmeter will tell you there is no flow between the two terminals.

Fixing of a Constantly Rotating Radiator Cooling Fan


After detecting a broken relay, you can try fixing it on your own or hiring an experienced person to help you. If you plan to do it yourself, you only have to remove the old relay and replace it with a functional one. It will not take more than a few minutes, and buying a new relay does not cost much.

– Repair Defects in the Cooling System

You can check individual parts of the radiator, look for signs of damage or leakage and then repair them. For example, you can check the wires, coolant reservoir, refrigerant sensor, etc.

The wires usually lose insulation, and you can see it if you observe the whole system. It is better to get them replaced by a mechanic. Similarly, a defect in the RPS also requires you to take the car for service.

– Test and Fix CTS and ECU

Before fixing a faulty radiator, you need to check how long should radiator fan stay on. The CTS and ECU have default settings that define the minimum temperature to start the radiator. These settings vary for each car model, but if the engine is colder than that set value, you can take other steps to fix the broken radiator.

The car shows an error if there is any fault in the control unit. You can also check the CTS using a voltmeter and examine the terminals. Fixing these units is not easy for a layperson, so you should ask for professional help.


1. Why Does My Radiator Fan Stay on When My Car Is Off?

Your radiator fan stays on when the car is off because of reasons such as an unclean radiator, a broken vehicle part, or an overheating engine. There can also be an issue with the ECU or the temperature sensor of the radiator.

2. Should Radiator Fan Run All Time When the Air Conditioner Is On?

No, the radiator fans should not keep running all the time when the air conditioner is on. It only happens if there is a leakage of the refrigerant in the air conditioner. On top of that, if the RPS fails, the fan also moves constantly.

3. How Long Should Your Car’s Fan Run After Turning It Off?

Your car’s fan should run for around 2 to 3 minutes after turning the engine off, but in some cars, it stays on for up to 5 minutes. Thus, the time depends on the car model. If the engine overheats, the car takes up to 10 minutes to cool down.

4. How Do You Make Your Radiator Fan Run All the Time?

To make your radiator fan run all the time, you can fuse the two wires in the fan connector together. Although this might help if you have an overheating issue with the engine, take note that it can also drain the battery.

Thus, it is better to fix the engine otherwise the car battery may drain. This is the answer if you’re wondering how to make radiator fan run all the time.

Conclusion of Why Does My Cars Radiator Fan Run Constantly

Could a Car’s Constantly Running Radiator Fan Lead to a Need to Reset the Car Computer Without Disconnecting the Battery?

A constantly running radiator fan in a car can indeed lead to a need to reset the car computer. When the fan runs continuously, it may cause the car’s computer system to become overwhelmed or encounter errors. To resolve this issue, a reset car computer may be necessary, without disconnecting the battery.

Is a Constantly Running Radiator Fan a Symptom of a Car Overheating Issue?

A constantly running radiator fan can be one of the common triggers of car overheating. While the fan is designed to cool down the engine, if it keeps running even when the car is not stressed, it may indicate an overheating issue. It’s essential to check for other signs like a rising temperature gauge or steam coming from the engine to confirm the problem.


After reading all the reasons, you now have the answer to “Why does my cars radiator fan runs constantly?”

You also know how to fix these problems, but first let us have a glance at the main findings:

  • A faulty CTS, relay, or broken fan motor part may keep the cooling fan spinning.
  • The engine may overheat because of the low coolant level and keep the radiator on for a long time.
  • Wash the radiator and check the coolant and refrigerant levels to fix the radiator.
  • Bring your car to a mechanic to replace damaged components such as CTS and refrigerant sensors.

So if the radiator fan runs when engine is cold, you can now fix it at home or bring the car to a mechanic.

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