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Home | Engine | Why Does My Radiator Fan Stay on When My Car is Off

Why Does My Radiator Fan Stay on When My Car is Off

February 11, 2024 | Victor Lukasso
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One common concern among car owners is the surprising incident of their radiator fan staying on even when the engine has been turned off.

Although, it’s normal for your radiator fan to stay on for 6 minutes or less after turning off the engine because it helps cool down the engine by drawing air through the radiator, dissipating excess heat.

However, when the radiator fan stays on for a more extended period, let’s say 10 minutes and above, it becomes a cause of concern.

This is usually a complex issue because it involves the vehicle’s cooling system and could result in potential engine damage if not fixed on time.

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In this article, we’ll explore possible reasons why the radiator fan of your car may remain on when the vehicle is off and how to address the situation.

Also, if you notice that your radiator fan is constantly running, you may want to read to the end.

What Happens if the Radiator Fan Stays On?

The radiator fan’s main job is to ensure the engine operates at optimum temperature. Typically, the fan is controlled by a computerized system called the ECM (Engine Control Module), which activates the fan when the engine reaches a specific temperature, the provides additional airflow into the system.

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Suppose the radiator fan stays on even after turning off the car. In that case, it can lead to potential issues such as a drained vehicle battery, increased fuel mileage, and increased risk of engine overheating.

While immediate damage may not occur, it’s advisable to diagnose and fix the issue promptly to prevent damage to the engine.

Why is My Car Radiator Fan Not Stopping?

If your car radiator fan is not stopping, it could be due to several reasons. Potential causes include a malfunctioning temperature sensor, electrical problems, low coolant level, or issues with the cooling system.

Why is the Radiator Fan Running After the Car is Off?

As I said earlier, your radiator fan running after turning off the engine should only be a concern if it stays on for more than 10 minutes.

It’s even worse if your radiator fan constantly runs, irrespective of whether your engine is on or off.

Here are factors that contribute to this issue.

Low or Leaking Coolant

If the coolant level in your reservoir is low or empty, the radiator fan may take longer to stop. This may even cause the fan to stay on indefinitely.

The logic behind it is that the ECM can’t tell the engine’s temperature. Thus, it uses that of the coolant to estimate its temperature. Therefore, if the coolant is empty, the radiator fan has to keep spinning as a defense mechanism to keep the engine from damage.

If this is the case with you, you may consider filling the reservoir with enough coolant and sealing leaks in the system, e.g., coolant leakage from the water pump.

Bad Cooling Fan

If the fan is bad, probably due to a broken blade, a short circuit, or a blocked airflow, it’ll take more time to dissipate heat from the engine.

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You can try replacing damaged fan blades and motors or check for electrical troubles.

Faulty Cooling Fan Relay

The task of the relay is to convert low-voltage signals from the ECM. It controls the power supply to the engine’s Cooling fan.

When the relay goes bad, it may send excess power to the cooling fan, keeping it on even while the engine is off. In another case, the cooling fan will be inactive.

Residual Heat

The heat on the engine after turning off the engine may be a bit above the required temperature to turn the fan off. In this case, the fan will continue working until the engine cools to a specified level.

Defective PCM or ECM

The power control and engine control modules handle most car functions, including electrical ones.

When the PCM or ECM doesn’t transmit accurate readings from other vehicle components, some components will behave abnormally.

A Cracked Radiator

If a radiator suffers cracks due to accidents, overloading or inadequate maintenance, it’ll cause the coolant to leak.

Leaking Thermostatic Housing

The thermostat housing regulates the flow of coolant to and fro the engine. When it starts leaking, the coolant level will drop, causing the fan to run constantly.

Electrical Faults

Problems with the electrical wiring, such as a short circuit, can disrupt the proper functioning of the fan control system. In such cases, the fan may remain on due to a false signal being sent to the fan relay.

Rusted Coolant Bypass Hose

The coolant bypass hose helps direct coolant flow to the engine. If the pipe is broken, damaged, or rusted, the coolant won’t get to the engine, thus leading to overheating, which can keep the radiator fan constantly on.

Leaky Heater Core

A heater core keeps the car’s cabin warm with coolant from the engine. If there happens to be a leak on the heater core, the coolant level will drop.

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This will likely result in overheating, which will keep the radiator fan on for longer.

Worn Radiator Hoses (Upper and Lower)

The task of the radiator pipes is to move coolant between the engine and the radiator and back to the water pump.

It’s advised to regularly scrutinize these pipes for wear and damage during routine checks.

What to do if the radiator fan is running after the engine is off

If you encounter a situation where the radiator fan remains on after turning off your car, consider the following steps:

Wait

If the fan keeps running for a short time after turning off the engine, it may be due to excess heat. Wait a few minutes for the engine to cool off naturally; the fan should eventually turn off.

You can open the bonnet to allow air into the engine.

Disconnect the Battery Terminal

If the fan keeps running for a more extended period, then the best you can do is disconnect the negative terminal of your car’s battery.

This will help save your battery and prevent drainage.

Add Coolant

If the coolant level on your car is low, you should top up the coolant. This will help cool your engine even faster.

You can also check the system’s fan relay and wiring harness. If the issue persists, you should seek a mechanic’s attention.

FAQs

Should the radiator fan run when AC is off?

Depending on the engine’s temperature, the radiator fan may or may not run. However, with the AC turned off, the engine temperature should go below 200 degrees, and turn the fan off.

ALSO, READRadiator Fan Not Working When Is AC On {SOLVED}

Does the radiator fan always run?

No, the radiator fan doesn’t run until the engine reaches a specific temperature. The task of the fan is to dissipate heat from the engine.

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Meet Victor Lukasso, the owner of V. Auto Basics. Through this blog, Victor Provides Insights on the latest tips, maintenance, repair, and techniques in the automotive world.

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