Why Radiator Fan Runs When Engine Is Cold – Guide 2023

Have you ever started your car on a chilly morning only to hear the radiator fans turn on immediately, even though the engine wasn’t yet warmed up? It can be confusing and even concerning for some drivers. After all, why would the radiator fan runs when the engine is cold? In this post, we will discuss this problem and explore why radiator fans sometimes turn on before your engine has reached operating temperature. So buckle up because we’re about to shed some light on one of the quirks of automotive engineering that have left many drivers scratching their heads!

radiator fan runs when the engine is cold.

If you notice that your radiator fan is running when the engine is cold, there are a few possible causes.

Faulty temperature sensor

If your radiator fan runs when engine is cold, it could be due to a faulty temperature sensor. The sensor may signal the fan to turn on even when the engine is not heated up yet. It can cause the fan to run unnecessarily and use up more energy than necessary. If you think your temperature sensor may be faulty, it’s best to take your car to a mechanic or dealership for diagnosis and repair.

Solution

If you suspect a faulty temperature sensor, the best solution is to take your car to a mechanic or dealership for diagnosis and repair. The technician can inspect the sensor, test its functionality, and replace it. Additionally, they will be able to identify any other issues contributing to the radiator fan running unnecessarily.

Stuck fan relay or switch

If your radiator fan comes on when the engine is cold, it could be a sign that the fan relay or switch is stuck. This can happen if the switch gets shot up with dirt and debris or worn out. If you suspect your fan relay or switch is stuck, you can try cleaning it with an electrical contact cleaner. If that doesn’t work, you’ll need to replace the switch.

Solution

1. Disconnect the fan relay or switch by unplugging the wiring harness.
2. Spray the relay or switch with an electrical contact cleaner to remove dirt and debris.
3. Reconnect the wiring harness and test the fan to ensure it works properly.
4. If the fan doesn’t work, replace the fan relay or switch with a new one.

Malfunctioning thermostat

If your car radiator fan runs when engine is cold, it’s likely because your thermostat is malfunctioning. The thermostat controls the coolant temperature in the engine; if it isn’t functioning properly, the coolant may become too cold and cause the fans to turn on.

There are a few signs that your thermostat may be malfunctioning, including:

• The engine takes longer than usual to warm up
• The engine overheats quickly
• The engine temperature fluctuates erratically

If you suspect your thermostat is malfunctioning, a mechanic must check it out immediately. A faulty thermostat can lead to severe engine damage if left untreated.

Electrical wiring issues

If your car’s radiator fan runs when engine is cold, there may be an electrical wiring issue. Check the wires leading to the fan for any fraying or damage. If you find any, replace the wires as soon as possible. If the wires look fine, then there may be a problem with the fan itself. Try replacing the fan to see if that fixes the issue.

ECU Wrong Signals

A few different things can cause the radiator fan runs when engine is cold; one is wrong signals from the ECU.

When the ECU sends a signal to the radiator fan to turn on, it completes a circuit. If there is a break in that circuit, the fan won’t receive the signal and won’t turn on. The most common way this circuit gets broken is by a faulty connection at one of the ECU’s pins.

Solution

The first step is to inspect the ECU pins and look for any signs of corrosion or damage. If the problem is visible, then you can replace the faulty pin. Use an ECU scanner to look for any additional potentially harmful signals coming from the ECU if there isn’t any visible evidence of damage. Once you’ve determined what’s causing the problem, you can fix it or replace the broken part.

Air pocket in the cooling system

There is a high probability that the cooling system contains an air pocket if your radiator fan runs when  engine is cold. This may occur if the thermostat is malfunctioning or the coolant level is low.

The engine could overheat if there’s a pocket of air in the system. The fan will help remove some heat, but it can’t do its job properly if no coolant flows through the system.

Solution 

1. Check the coolant level: Ensure the coolant is filled to the recommended level in the radiator and overflow tank. Top off or replace as needed.
2. Check the thermostat: Ensure it is opening properly and not stuck open or closed. If necessary, replace it with a new one.
3. Bleed/burp the system: Using a funnel and siphon to remove air pockets from the cooling system. Start by filling up the radiator and overflow tank with coolant, then start up your engine and let it idle until warm, then turn it off again and ensure both tanks are filled to their respective levels. Repeat this process until no more air bubbles appear when checking either tank.

Bad Radiator fan motor

As air is drawn through the radiator to disperse heat from the coolant, the fan blades are powered by the cooling fan motor. Based on the engine’s temperature, the ECM manages the motor.

The cooling fan may turn on while the car is cold as a result of internal electrical issues with a damaged cooling fan motor. When that occurs, the fan behavior is ridiculous. It might make a different sound and turn on and off by itself.

Solution

• Ensure that the engine is cold. After that, take the battery terminals off.
• Remove the cooling fan assembly and disconnect the electrical connector.
• Check the motor’s functionality by testing it using a multimeter, a battery, and jumper wires.
• If the motor is defective, replace it with a new one, then rebuild the cooling fan assembly.

Also Read: How Long Can You Drive without A Heatshield

Final Thoughts

If your car radiator fan runs when engine is cold, it’s not good. Please immediately fix it, or it can cause the radiator fan not to run at the proper time. It can cause your car to overheat while driving and harm other engine components.

Frequently Asked Questions

How can I determine if the fan relay or switch is malfunctioning?

If your radiator fan runs when engine is cold, it could be a sign that the fan relay or switch is malfunctioning. Here are a few ways to determine if the fan relay or switch is indeed the issue:

1. Check for power at the fan connector. Use a voltmeter to test for power at the fan connector. If there is no power, the problem is likely with the fan relay or switch.
2. Check for continuity between the terminals on the fan relay or switch. Use a multimeter to test for continuity between the terminals on the fan relay or switch. The problem is likely with the fan relay or switch if there is no continuity.
3. Check for the voltage drop across the terminals on the fan relay or switch. Use a voltmeter to test for voltage drop across the terminals on the fan relay or switch. If there is a voltage drop, the problem is likely with the fan relay or switch.

What temperature triggers the cooling fan to activate?

The engine cooling fan is designed to keep the engine coolant at the correct temperature. The fan will turn on when the engine coolant temperature reaches a certain point, usually around 200 degrees Fahrenheit. The fan will turn off when the engine coolant temperature drops below that point.