How to check if a radiator fan is working properly?

Author: Sonny Frami  |  Last update: Tuesday, January 6, 2026

Testing Methods For the Radiator Fans You can use the car battery to test the cooling fan for issues. You can also check the fan's commutator for open circuits. If it stops on a “dark” spot, the fan won't run then and the problem will be intermittent.

How do I test my radiator fan?

Quickest test would be to unplug the radiator fan, run 1 wire each from the pos. & neg. battery terminal, and touch one to each terminal on the fan plug (DO NOT touch them together). It should run. If it doesn't, bad fan.

What tells the radiator fan to kick on?

The engine temperature should trigger the fan to turn on. It will also turn the fan off once the engine has cooled to under 200 degrees. You may have heard of a part called the radiator fan switch or temperature fan switch. This is linked to a thermostat and works much like your home's HVAC system.

How to tell if a radiator fan switch is bad?

Warning lights. If the cooling fan relay has failed, you may see warnings, such as the check engine light and the temperature warning light, pop up on the dash, but first, you may notice that the A/C stops cooling.

How do I know if my radiator fan resistor is bad?

What common symptoms indicate you may need to replace the Cooling Fan Resistor?
  1. Cooling fan never stops running even with the ignition off.
  2. Cooling fan never kicks in and engine temperature increases abnormally.

HOW TO TEST A CARS COOLING FAN TUTORIAL

How do I know if my radiator fan clutch is bad?

A healthy clutch will offer some resistance. If thе fan spins frееly without drag, or if it fееls excessively stiff, it's a sign of a failing fan clutch. Regular resistance tests can help catch problems early before they escalate.

How can I test my radiator fan without a multimeter?

You can use the car battery to test the cooling fan for issues. You can also check the fan's commutator for open circuits. If it stops on a “dark” spot, the fan won't run then and the problem will be intermittent.

Should radiator fans push or pull air?

Radiator thickness and number of fins per inch (FPI) increase heat dissipation surface, but also make it harder for the fan to blow air through it. So the more FPI and the thicker the radiator is, the higher the heat dissipation increase will be by having fans in push-pull configurations.

How do I know when to replace my radiator fan?

1. Check if your car's overheating
  1. Your check engine light may turn on.
  2. There may be steam coming from the hood.
  3. If your car has a temperature gauge, then this will also indicate an increase in temperature.

What sensor turns on the radiator fan?

Coolant Temperature Sensor

Both systems use a temperature sensor to determine when to start the fan. If the temperature sensor is faulty, the control unit doesn't interact with the radiator correctly. Some cars have a separate engine coolant temperature sensor for the radiator fan and the engine control unit.

Why is the fan not kicking on my radiator?

Check the coolant temperature sensor.

A signal from the coolant temperature sensor is what triggers the ECU to turn on the radiator fan, and if it's faulty, it can prevent the fan from working at all.

How do I check my fan problem?

  1. Check and clean air vents.
  2. Provide proper ventilation.
  3. Run a hardware diagnostic test.
  4. Update the BIOS and device drivers.

How do I check if my radiator is bad?

Engine Overheating

If the temperature gauge in your vehicle is rising higher than usual or if the engine warning light comes on, these are both indications that your radiator needs to be checked out. Another sign of radiator damage is a leak in the system.

Should I be able to hear my radiator fan?

Your radiator fan should be audible. However, it should not be so loud that it sounds like a plane priming for takeoff, drowns out conversations anywhere near it, or scares children off the street whenever you pull onto the block.

Does blowing a fan on a radiator work?

Small radiator fans work by being fitted underneath designer radiators and blowing air upwards. Essentially, they can enhance the level of heat delivered to a specific room by boosting the standard convection attributes of the rad. They are an especially helpful addition for smaller spaces.

Should there be air in a radiator?

Most radiators will have a small amount of air in them, especially over time but even during the course of the heating system or radiator installation, some small bubbles of air may creep into the system. They can be created when your radiators are initially filled with water and a little air may remain in the system.

How do you check radiator pressure?

Generally, it attaches to the radiator where the radiator cap goes, and you pump it by hand until the pressure on the gauge matches the pressure that is written on top of the radiator cap. Typically on a modern vehicle this pressure is between 13 – 16 psi. Let the vehicle sit with this pressure for 20 – 30 minutes.

What is the difference between radiator fan and cooling fan?

The radiator fan is a type of fan used in automobiles to cool the radiator. By doing so, it helps with regulating engine temperature. It's, therefore, also known as the engine cooling fan and usually mounted between the radiator and engine. In some vehicles, the fan sits between the grille and the radiator.

How do I know if my fan clutch is stuck?

A locked-in, or seized, fan clutch can cause radiator fans to fully engage at all speeds. Therefore, you could experience a constant droning noise from the fan at a higher volume than usual. You might notice more dust being blown from under the vehicle than normal when idling.

How to tell if a water pump is bad?

Symptoms of a Failing Water Pump

Overheating is an obvious symptom of a failing water pump. Drivers should make sure the needle on the engine temperature gauge doesn't go into the red. A warning light should also illuminate to tell the driver the coolant is getting too hot.

How to tell if a clutch is bad?

A clutch that sticks can cause grinding noises or can keep your vehicle from going into gear while a clutch pedal that is stuck to the floor renders your vehicle undriveable. If either of these situations happens to you, a trip to your mechanic is in order.

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