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Radiator Fan Problems, How to Test Radiator Fan

broken radiator fan
broken radiator fan
Resource: https://forum.ih8mud.com

When your car engine overheats, the reason is likely radiator fan problems. Being able to identify these problems helps, as you will be finding out in this article. Among the things we will be discussing is what causes a cooling fan not to work and the changes when that happens. We will also be explaining how to check if a radiator fan is working using readily available tools and a simple procedure.

Radiator Fan Problems, What Causes a Radiator Fan not to Work?

There are many reasons why your car’s radiator fan is not working. It depends on the type of fan, though, and varies between mechanical and electric cooling fans. Let’s see some of the causes and what you can do when you first notice them. Your engine cooling fan will not work properly because of any of these reasons.

  • Bad Radiator Fan Relay- this component is found in electric cooling fans. Over time and when exposed to current and heat, it often goes bad and stops working. A burned relay will also cause the fan to run without stopping.
  • Blown Radiator Fan Fuse– the fuse protects the fans wiring system and electrical parts. If it blows, the fan will no longer receive current and stops working. The fuse blows as a result of excessive current or shorting.
  • Bad Wires and Connectors- besides the fuse and relay, an electric radiator fan depend on cables and connectors to convey current. When these wires break or fray, current flow is interrupted. Connectors can break, accumulate dirt, or become loose and cause radiator fan problems.
  • Faulty Control Module, Temperature Switch and Sensors- electric radiator fans are controlled by complex electronic systems that comprise an ECU, a temperature switch, coolant temperature sensor and several other sensors. These can fail and cause the fan to operate abnormally.
  • Bad Radiator Fan Motor- this is one of the major reasons for the radiator fan not working. The motor fails when the brushes and bearings wear out or if the armature coil burns out. From the buildup of dirt too, or burned spots on the commutator.

A mechanical cooling fan fails differently, since it uses different components. If your car uses one, you’re likely to encounter these problems.

  • Damaged Radiator Fan Belt- if using a mechanical fan, the problem could be a broken belt. The belt transfers motion to the pulley that operates the fan. A damaged radiator fan belt is therefore one of the possible reasons why you’re experiencing overheating problems with your car.
  • Worn or Damaged Clutch- again, this problem happens on mechanical engine fans. A radiator fan clutch can wear down over time, or go bad in any other way. Damage or wear leads to several radiator fan problems such as freewheeling or continuous engagement.
broken radiator fan with rusted motor assembly
broken radiator fan with rusted motor assembly
Resource: https://www.seatcupra.net/forums

Bad Radiator Fan Symptoms

How can you tell if you have a bad radiator fan? Several things happen when you have a failing cooling fan on your car. Common ones include the following.

Radiator Fan Not Spinning

The radiator fan does not come on at all, even when the coolant temperature rises. If using an electric fan, the problem is often due to a blow fuse, bad relay, broken wires or connectors, and burnt out motor. It means the fan is not receiving current, and is one of the most common radiator fan problems. Luckily, all these components are replaceable including thee motor itself.

Radiator Fan Works Intermittently

The cooling fan works intermittently causing occasional overheating problems. This happens when you have a defective control module, loose connectors, or faulty sensors. To pinpoint the problem, check the sensors for resistance using a digital multimeter. For the control module, you need a diagnostic scanner to read the generated trouble codes. The sensors and ECU are replaceable parts and only need changing when damaged.

Radiator Fan Runs Slow

The radiator fan runs slow, and is often unable to cool the radiator as needed. This occurs when the motor is not receiving full power. Reasons for that include faulty wires and corroded or dirty connectors. A worn motor is also one of the causes of reduced cooling fan speed. Remedies include replacing the faulty wires and connector or changing the motor.

Radiator Fan Runs Without Stopping

You have the cooling fan running without stopping. This is occurs due to a bad radiator fan relay, faulty radiator fan module, or defective temperature switch and sensors. The problem is normally corrected by checking these components to see if they are working and replacing them if necessary. If you have an engine-driven cooing fan, the clutch can get stuck and cause the fan to spin continually. The clutch is also replaceable.

Radiator Fan Making Loud Noise

There’s audible radiator fan noise. This problem affects both engine-driven and electric fan. Causes include broken fan blades, worn motor, or damaged radiator fan clutch. Because a loud cooling fan is often an old one, many motorists choose to replace the entire fan assembly. You can also change the blade assembly, clutch, or motor to correct cooling fan noise.

Radiator Fan Clutch Leaking Fluid

This is one of the radiator fan problems that affect mechanical or engine-driven fans. You will notice fluid coming from the fan’s clutch, which indicates a broken clutch and a fan that will not work correctly. The problem leads to the radiator fan not spinning when it should, such as when driving at slower speed or when the engine is running. Replacing the clutch will correct the problem or you can change the fan.

Check Engine Light

The dashboard light comes on to signal a problem with the engine. This is a general radiator fan not working symptoms and usually triggered by overheating. It can also mean other problems than a bad cooling fan. When the light comes on consider checking the engine fan to see if it’s working correctly.

Engine Overheating or Overcooling

The engine temperature rises to higher levels than normal, or remains lower than usual. This indicates a fan that’s not working, working intermittently, or one that comes on at the wrong time. Causes include faulty sensors, bad temperature switch, defective control module, bad relay and blown fuse. The best thing to do is check these components and replace the damaged ones.

How to Test a Radiator Fan

The radiator fan motor is one of the parts that go bad and cause the fan to stop working. As such, testing the motor helps you to make the important decision of whether to repair or change the fan. A radiator fan test is also easy to perform and does not require any expert knowledge. The steps below explain how to test a cooling fan using a multimeter or car battery.

how to test radiator fan with multimeter
how to test radiator fan with multimeter
Resource: https://www.youtube.com

How to Test Radiator Fan with Multimeter

  • Locate the fan on your car. It’s usually near the radiator.
  • Remove the fan motor connector
  • Identify the terminals that supply current to the motor
  • Set the multimeter to read volts by moving the rotary switch
  • Connect the multimeter probes to the terminals on the connector
  • Check the multimeter. If it reads around 12 Volts but the fan is not working, you have a burned out motor. If there’s not voltage, the problem is the fan’s wiring system. Consider checking other components such as the fuse and relay. Check the wires and connectors too.
testing radiator fan using a battery
testing radiator fan using a battery
Resource: https://www.youtube.com

How to Test Radiator Fan with Car Battery

  • Find the cooling fan next to the radiator or use your car manual to locate it
  • Unplug the connector
  • Use jumper wires to power the motor directly by connecting it to the car battery
  • If the motor spins it’s in good condition and the problem is either a blown fuse or bad relay. If could also be bad or loose connector and broken or frayed wires.


Radiator fan problems cause your car’s cooking system to malfunction and can be the reason for engine damage. To prevent overheating or overcooling issues, it’s important that you catch the problems early enough. The bad radiator fan symptoms described in this chapter will help you to do that. Read the next section to learn how to deal with the cooling fan issues listed here

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