What Causes A Radiator Fan To Run Constantly?

Radiator fans are designed to turn on when the temperature in your car engine reaches a certain level (around 200 F). So what will happen If your radiator fan runs constantly even when the car engine is off? Read the article and you will find a couple of reasons and how to fix this problem.

When Is Your Radiator Fan Supposed To Kick In?

The car radiator fan has the function of coordinating with the coolant to help cool down your engine during operation. Although it is only a small part, thanks to that, the car engine works more efficiently and stably. The cooling fan is activated in 2 ways:

Method 1: Use a thermostat: The thermostat is located between the engine and the radiator to help control the temperature. When the coolant temperature reaches a certain threshold, and the engine rotates at full rpm, the radiator fan will operate.

Method 2: Using the electrical system: When the coolant in the engine starts to heat, the electrical relay switch is activated causing the cooling fan to operate.

Understanding simply: The engine temperature will activate the radiator fan to turn on. And your fan will turn off once the motor has cooled down below 200 degrees. When your coolant reaches about 200-230 degrees, the radiator fan will start on. Normally, it will take 15-20 minutes for the radiator fan to turn on after the control valve is off. 

radiator fan keeps running when car is off
The radiator fan keeps running when car is off: What should I do? (Photo: merciej.com)

Why My Radiator Fan Runs Constantly.

Are you probably concerned that why does my radiator fan keep running? There are many things that can happen to your engine fan. It might be the blown fuse and it will be cheap and easy for you to fix when the radiator fan has trouble with this problem. But more difficult and complicated in the situation that the temperature sensor broke making your fan turn on too early and not stop running. To know more detail about what are the reasons behind the scenario, keep reading:

Faulty temperature sensor

The cause of the radiator fan running continuously may come from the temperature sensor, which is the part that determines when the radiator fan must operate. The coolant temperature sensor is a thermistor and its resistance changes when the coolant temperature changes. When resistance changes, the signal is sent to ECU and it will determine when to activate the radiator cooling fan when a certain temperature is met. And when the temperature sensor did not operate properly, the consequence is that the signal to sent the computer is incorrect and makes your coolant keep running. This problem can be fixed by finding the location of the temperature sensor, trying to disconnect the wire, or connecting to another sensor.

Stuck fan relay

An important reason that we can’t help but mention is that your car had an issue with the cooling fan radiator. Think of the cooling fan relay as the main display that controls the operation of the cooling fan. If this part doesn’t work, there’s nothing preventing the fan kick in as the engine temperature drops to the required threshold. To know the exact level of the relay’s damage, you can use the VOM meter to measure the relay voltage. If the meter is only 12V, it is normal, otherwise, the relay is damaged and needs to be replaced. Identify the location of the relay from the fuse box then pull out the problematic relay.

Defective fan switch

You’ve probably heard of a component that’s called a cooling fan switch. This system is linked to the thermostat and works just like the HVAC system in your home. If either of these components fails – your radiator fan turns on continuously and this causes serious problems. The function of a fan switch is similar to the coolant temperature sensor work. It means that when a certain temperature is met, the fan switch will send the signal to the computer and activate the cooling fan.

Having trouble with the ECU unit

ECU unit performs the task of processing data and controlling the activities that take place inside the engine car. When this part has a problem, the operation of the vehicle will immediately be interrupted. As a general rule, the ECU will send the signal to the fan to kick off if the cooling system is still hot. The ECU tells the fan when to turn it on or off. When a faulty ECU, it cannot tell the cooling fan when to turn off.

Short in the electrical wires 

If you check that the engine has cooled down and the radiator fan is still running, the negative wire is most likely damaged. If the engine design provides for two coolant temperature sensors, then if the “minus” sign of the first sensor fails, the fan will run on ignition. In case of insulation failure of the wires of the second coolant temperature sensor, the fan runs continuously while the engine is running. At this time, the user of the vehicle needs to unplug the two poles of the wire and check the operation of the current through the voltmeter. If no power goes through, the wire is damaged. In addition, this way also helps users locate the fan relay on the hood. Check the current from the relay to the fan, if the power appears there, it means that the car cooling fan has a problem.

Damaged fan clutch

The fan clutch works to attach the radiator fan to the engine system and make the motor run. The fan will operate not properly if the clutch is going bad. The wear and tear after a long time of use cause the clutch spring to corrode. When the springs are corroded, it will interrupt the movement of the engine and can make your car not run.

>> Read more: 8 Common Symptoms of a Clogged Radiator You Must Know

What Happens If A Radiator Fan Keeps Running When Car Is Off?

why does my cooling fan keep running
You probably concerned that why does my radiator fan keep running? There are many things that can happen to your engine fan. (Photo: cashcarsbuyer.com)

The answer depends on the duration that your radiator fan runs. It will be a normal situation if after running your engine, the water in the radiator is hot and needs to be cooled down. Once you turn off the engine, the car’s computer senses that the radiator is at a higher temperature and still needs to dissipate heat. But if your radiator fan stays time generally more than 2 minutes, then contact service repair. There is probably a part that can go wrong.

If the fan runs for a long time, the fan can be damaged due to overuse. The purpose of designing this part is only to turn it on and off when necessary and if the radiator fan runs continuously, this will shorten the lifetime of this component, and more seriously, it can make drain off your battery causing your car not to start. On the market, most fans of modern cars have a module that tells you when to turn them on and off. Maybe you have a faulty module or relay in your car.

How To Prevent When Your Radiator Fan Runs Constantly?

The cooling process for cars plays a very important role, no less than engine lubrication. Therefore, besides paying attention to monitoring and changing the car’s oil periodically. You also need to regularly check the radiator fan control system to ensure that this part always operates well. Below are instructions on how to check the basic radiator fan to help limit the condition of the fan running continuously:

Inspect and clean the radiator fan

Drivers should test the fan by opening the car hood, starting the engine, and setting the air conditioner to the highest temperature. At the same time, you should monitor the temperature gauge to make sure that the overheating motor does not overheat. 

If your radiator, both the main and the A/C radiator, is covered by dirt, the heat exchange process will be disturbed. As the consequence, the fan must spin almost continuously to cool the system. Cleaning the fan is a very important step. You can use the degreaser to remove all the dirt on the fan housing and also the blades.

Fan wiring and power supply

After cleaning every space of your radiator fan, please check the wiring and power supply. These are two types of positive and negative wires that provide power to the fan. Drivers need to unplug the lead from the fan and check the connector for damage, corrosion, or poor connection.

Check the car coolant

One of the simplest ways to make sure your fan isn’t damaged is to inspect your coolant. This is very easy you can do to ensure your engine runs at the optimum temperature. Just open the hood and check the level of the coolant. This has min and max markers on it. The standard liquid level to help your fan work properly should be between these two levels. 

When all parts don’t have abnormal signs, don’t forget to diagnose the ECU unit. If it happens to your car, disassembling and dismantling the ECU is the necessary step. After that, you should inspect the internal board inside ECU and you can even clean it with oxides with alcohol.

>> Related post: Car Radiator Fan Not Working: Troubleshooting 6 Common Problems

Closing Thoughts: Why Does My Cooling Fan Keep Running?

In order for the radiator to cool the car system. A large amount of air is required to pass through the aluminum fins. The radiator fan creates the necessary airflow and increases air circulation when entering the radiator, helping to cool the engine more efficiently. When the cooling fan runs constantly, it will affect the performance of your engine. And more serious consequences can happen so it is necessary to detect this problem in time. However, there are many reasons that cause this phenomenon that sometimes make it hard to diagnose exactly the cause. Through our article, we hope that it will partly help to handle this problem.