Fan Still Running When Car is Off – Why Does This Happen?




The car’s fan is a crucial component of its cooling system, as it pulls the cool air to lower the engine’s temperature. You probably won’t hear the fan when it’s running while you’re driving a new car, but it starts working when the internal temperature reaches 200 degrees Fahrenheit. 

But it’s common to hear the fan still running when the car is off. Why does this happen? Does this mean that you should contact a professional for help?

I know that old cars come with many issues, so if you have an old vehicle, you might be worried when you hear the fan operating if you have an old vehicle. I’ll explain the possible reasons why your idle car’s fan might be noisy and what to do about it. So, keep reading to learn more about this topic. 

Why Does My Fan Keep Running When My Car is Off?

The car’s cooling system isn’t just made of the radiator and the coolant. There’s also a fan connected to the radiator, and it operates to keep the engine cool. 

When you turn on your car, the engine heats up, which triggers the fan’s switch. This switch acts like the thermostat in an HVAC system, and it triggers the fan to work. 

If your car’s engine overheats, there’s probably a problem with this switch. There could also be a coolant leak, a bad water pump, or low engine oil.

Ideally, the fan will switch off once the engine’s temperature has cooled below 200 degrees Fahrenheit, and this guarantees that your vehicle’s cooling system is operating as it should. 

So, why does the fan keep running when the car is off? This can happen in the following cases. 

  • It’s normal because the engine is so hot, so the fan has to operate for several minutes to cool it off. 
  • You have a coolant leakage or another cooling system issue, and the system doesn’t operate as it should, so the fan will have to work harder and longer. 
  • Your car is off, but the AC is still on, which means the engine is running. 
  • There’s an electric issue that keeps the fan on, even when the engine is cool. In this case, it might continue to operate until it has drained the battery. 

It’s Normal

The radiator’s fan is a crucial component of the cooling system. Without a functional fan, the vehicle’s engine will overheat and probably be damaged. 

It’s quite common for the fan to run for five minutes or sometimes longer to cool the engine off. It can work for a few more minutes if you’ve been driving in hot weather or for a long distance. 

If you have an old vehicle, it’s more susceptible to overheating than a new one. Older cars were made for people who drove much slower and for shorter distances than us. Although your car can still cope with driving in modern times, its parts must work harder. 

New vehicles are computerized and use the latest technologies. The engine and the internal cooling system are made from better materials and are more efficient, so the radiator’s fan won’t have to work for long periods after you switch off the car. 

Cooling System Issues

Cooling System Issues

Cooling system issues are probably why the radiator’s fan won’t shut off. A low coolant level, a coolant leakage, a cracked radiator, worn-out radiator hoses, a rusty coolant bypass pipe, or a faulty thermostat can all cause the fan to continue running when the engine is off. 

Before assuming your car is failing, checking the coolant level is crucial. Your coolant level is too low if it’s below the minimum sign. In this case, the fan must work harder to cool the engine. 

You might have added the wrong amount of coolant while maintaining or servicing your car. Adding a small amount until you reach the maximum sign on the coolant’s reservoir will solve the problem. 

But if there’s no coolant at all, there could be a leak or a hole in the system. This can be a crack in the radiator, a loose hose, a cracked hose, a broken pipe, or a faulty thermostat. Unfortunately, this means that no matter how much coolant you add, the system will still malfunction. 

In this case, you should take your car to a professional to fix it. A cracked radiator is usually caused by poor maintenance or an accident. The hoses and pipes naturally wear and should be tightened, repaired, or replaced. 

You might also have a cracked thermostatic housing or heating core. The thermostatic housing controls the coolant’s flow to the engine. When it’s broken or cracked, the coolant level will drop. As a result, the fan will work longer, attempting to cool off your vehicle’s engine. 

This might also happen if the heating core is cracked or broken. Corrosion or an accident might be the reason why the core broke. 

Finally, there could be a problem with the temperature sensors in your car. The sensor helps the cooling system work well by releasing the coolant when necessary. The fan might work unnecessarily if the sensor sends the wrong data to the engine. 

The AC is Running

Although the fan’s main job is to cool off the car’s engine, it also doubles as a condenser fan. The condenser is located right in front of the radiator, and the fan will keep the refrigerant cool. Moreover, the fan will continue to provide a constant airflow supply through the condenser. 

The vehicle’s AC system relies on a refrigerant, which turns into liquid in the condenser, passes through the expansion valve, and then turns into gas when it passes through the evaporator. 

Like the radiator, the condenser cools the temperature when cool airflow passes through it. This air cools the refrigerant, which keeps your car cool. Unlike the car’s radiator, which triggers the fan when the engine overheats, the fan will continue to run as long as the AC is on because there will be no airflow to cool the refrigerant. 

As a matter of fact, as soon as you start driving your car, the fan might turn off, as long as the engine isn’t yet hot enough. This happens because the natural airflow will keep the refrigerant cool. It might still operate if the outside air is too hot, though. 

Without an operating radiator fan, which doubles as the AC’s condenser fan, the pressure inside the pipes, condenser, and evaporator will rise significantly. You’ll hear loud noises, and the AC system might temporarily shut off. 

Electric Issues

Electric issues due to inadequate internal parts or connections can be the reason why your fan runs when the car is off. These are pretty common but also easy to fix once you’ve determined the cause of the issue. 

You might have a faulty or broken fan relay. This relay sends power to the radiator’s fan to operate it. When it’s broken, it unnecessarily sends power, keeping it running until it drains the battery. The relay usually breaks due to normal wear and tear, corrosion, or overheating. After replacing it, your fan should operate normally. 

A faulty ECU or PCM might cause your problem. The electronic control unit is responsible for operating several electrically operated components of your vehicle, including the windows, doors, lighting system, and fan. When it breaks, the fan might not work correctly. 

The powertrain control module is connected to the engine and transmitters. A faulty PCM will cause all the related parts to malfunction. Both components can become defective due to water damage or corrosion. Replacing them should solve the problem. 

Finally, having faulty wires will cause your radiator’s fan to work for longer periods, or it might not work at all. So, if you’ve checked all the other electrical components that connect to the fan, have a professional electrician check the wires and replace them if necessary. 

How Can I Tell that My Fan is Malfunctioning?

How Can I Tell that My Fan is Malfunctioning

The first thing you’ll notice is the loud noise. It’s quite common for a radiator’s fan to be audible, especially if you have an old vehicle. However, if the noise is too loud, then there’s probably something wrong. Ignoring it might damage the engine and cost you a lot of money. 

When Should I Replace My Fan?

The radiator’s fan is designed to last for the vehicle’s lifetime, and there’s no need to replace it even if it malfunctions. In most cases, you won’t have to change the fan because the problem is caused by something else. However, you might not have the needed knowledge or skills to determine what is causing the fan to malfunction. 

A professional will use a diagnostic tool to determine the problem with your vehicle. They might also have to examine several parts manually. 

Proper scheduled maintenance and replacement of the old parts can save you a lot of time and hassle, as some parts continue to work for long periods while they’re malfunctioning. You’ll notice that your car is operating, but there might be internal damage that you’re unable to detect. 

You might need to replace the fan if it was broken during an accident or due to lack of maintenance. Otherwise, fixing the previous issues guarantees that the fan will operate for years. 

Wrap Up

The fan is a crucial component of your vehicle’s cooling system. It’s designed to turn on and off while the car operates to regulate the engine’s temperature and protect it from overheating. 

It’s pretty normal to hear the fan’s sound when your car is running, especially if you have an old vehicle. New cars have better and more advanced components, and the fan usually runs smoothly. 

Hearing the fan running when you’ve switched the car off isn’t always a cause of concern. It might happen because the engine is too hot and will continue to operate for a few minutes. You might have the AC on, and the fan will continue to work to cool the refrigerant. 

However, there might be a problem with the car’s cooling system or electrical components. In this case, you should have a professional check the vehicle and replace the faulty parts. 

Claire S. Allen
Claire S. Allen
Hi there! I'm Claire S. Allen, a vibrant Gemini who's as bold as my favorite color, red. I'm a fan of two cool things: strolling the streets in a red jacket and crafting articles that connect with readers. With my warm and friendly personality, Claire is sure to brighten up your day!
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