Have you ever turned off your car only to hear the fans continue to run? While it may seem concerning, this is normal in many vehicles. Understanding why fans continue to run after the car is turned off and how long they should run for can help ease any worries.
Why fans continue to run after car is turned off
A car cooling fan, either mechanically engine-driven or electric, has some sort of controller that determines the engine is at a sufficient temperature to warrant turning on the fan and cooling the coolant in the radiator. Some cars feature a brushless fan that work in set stages. It will start to begin with at, let’s say 25% power, and then as the temperature increases, it ramps up to full speed to deliver its full cooling effect.
The thing to remember with cooling fans is they only provide efficient cooling when the engine is idling, or the vehicle is traveling below approximately 30mph. Once the car surpasses these speeds, the air passing through a radiator, providing the cooling required, is far greater than any fan can produce. This is why the car needs cooling most when the car is stationary after a long drive and will continue to run when the vehicle is off.
After a long drive, the motor and transmission will still be at a high temperature. Although the coolant is not being pumped around the engine bay, heat soak means the hot air given off by the motor will stay in the engine bay. Temperatures could remain or rise further, which could cause damage or reduce the lifespan of the motor and its supporting components. The fan’s job is to cool the engine and supporting components by removing the hot air from the engine bay area, lowering the ambient air temperature around the engine bay. There are several contributing factors as to why the cooling fan stays operating with the engine off; they are:
- Engine and radiator heat – Generally, a coolant temperature sensor will be located in the engine block or radiator, telling the car the coolant is too hot and the fan must start operating to cool it. With the engine off, this system still operates to protect itself, so the fan will remain running until the sensor temperature drops below the threshold.
- Climate control system – The air con system requires the use of a fan or the engine fan to cool the AC gas passing through the condenser at the front of the car; if the climate control is operational when the engine is off even, and you’re sat in the vehicle the cooling fan will also need to operate to provide the cool air.
How long fans should continue to run after car is turned off?
It’s normal for a car cooling fan to stay running after the car is switched on for approximately 5 minutes. But this is only if the vehicle has been idling for about 20 minutes or the car has been driven, and the engine is hot.
You should be concerned if the cooling fan is still operational and getting close to 10 -15 minutes. There are also a few other concerns you should be aware of that indicate another issue and the fan is being on after the car is shut off is not normal, they; they
- The engine temperatures aren’t dropping as indicated by the temperature gauge in the car
- The fan keeps shutting off and kicking back in again very quickly
- The check engine light is illuminated on the dashboard if you turn the engine back on
- The fan stays on but is spinning very slowly
What can cause a fan to stay on after the ignition is off?
Each of the below problems can cause the fan to run on for to long or indefinitely after the car is shut off.
- Faulty temperature sensor – The temperature sensor detects the engine temperature and sends a signal to the fan to turn it on or off. If the sensor is defective, it may signal the fan to stay on even when the engine is not hot. They can also have the opposite effect and the fan will not switch on regardless of the coolant temperature.
- Faulty fan relay – The fan relay controls the power supply to the fan. If the relay is stuck in the closed position, the fan will continue to run until the relay is disconnected.
- Low coolant level – The coolant is responsible for keeping the engine cool. If the coolant level is low, the engine may overheat, and the fan may stay on.
- Clogged radiator – A clogged or furred-up radiator can prevent the coolant from flowing properly, causing the engine to overheat and the fan to remain on for much longer than required after the car is keyed off.
- ECU problems – The ECU (Engine Control Unit) is responsible for controlling the fan. If the ECU is faulty, it may signal the fan to remain on after the car is switched off.
- Aftermarket fan controller – Aftermarket fan installations may use a fan controller instead of the ECU, which could’ve been wired incorrectly or gone faulty, meaning the fan is always on.
Regardless of what is causing the fan to stay on, the problem with it staying on for too long is the car battery will die, and you may struggle to start the vehicle again.
How to stop the fan if it stays on for too long
To stop a cooling fan that has been on for too long, first, you should try putting the key back in the ignition, start the car and turn it off again. If any switches or relays are stuck in the on/off position, they reset when the car’s ECU kicks back into action. If that doesn’t work, removing the fan relay should stop the fan from operating, but you need to know which relay to remove.
The Last way, which will 100% stop a fan is to disconnect the cars battery. As easy as that it is, its not the right way to do it because it can cause further problems, such as a potentially spiked ECU, loss of radio and resetting the cars dashboard.
You should never put anything into or touch the fan blades to try and stop them; not only will this damage the fan, but it can also cause severe injury!
It is essential to know that it is normal for a cooling fan to be operational after the car is switched off, especially if it needs it. The cooling fan shouldn’t stay on after the vehicle is off for more than 10 minutes, worst case. Any longer, and the car’s battery will start draining as it tries to keep the fan spinning. By that point, the car should’ve been cooled enough to switch off itself, so if it doesn’t, it’s obvious another problem needs repairing.