How to Diagnose a Bad Radiator Fan

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Symptoms of a bad radiator fan (and how to fix them)

Co-authored by Eric McClure Reviewed by Jason Shackelford

Last Updated: November 28, 2024 Fact Checked

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Causes & Solutions for a Bad Radiator Fan

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Signs the Radiator Fan Isn’t Working

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How does the radiator fan work?

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Can you test a radiator fan motor?

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Is it safe to drive without a radiator fan?

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Tips

The radiator fan is located behind (or occasionally in front of) your vehicle’s radiator. It is responsible for getting rid of hot air when your vehicle isn’t going particularly fast and there isn’t any wind to help extract the heat. If the radiator fan isn’t working, your engine may overheat. In this article, we’ll break down the likely causes—and the repairs—of a bad radiator fan.

Why a Radiator Fan Won’t Work

In most cases, a blown fuse or bad starter relay is responsible for a vehicle's radiator fan not turning on. However, a bad fan motor, a malfunctioning ECM, or wiring damage can also cause a fan to not turn on. If the bad radiator fan is causing your engine to overheat, avoid driving the vehicle.

Section 1 of 5:

Causes & Solutions for a Bad Radiator Fan

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1
Blown fuse Like every other electrical component in a vehicle, the radiator fan has a dedicated fuse. If that fuse is blown, the fan won’t be able to turn on. Refer to your car’s manual to find the fuse layout. Then, with a cold engine, pop the fuse box and gently pull out the fuse for the radiator fan. Hold it up to a light. If the wire inside is broken, replace the fuse. If the wire is connected, your fuse is fine.^{[1]
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- The fix: Purchase a replacement fuse for your vehicle and insert it into the port for it. If you don’t want to do it yourself, see a mechanic. This is an easy, fast fix for them.
- The cost: A new fuse shouldn’t cost you more than $10 or so. If you have a mechanic do this for you, it may run $50-150.
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Dead radiator fan motor The radiator fan has a dedicated motor responsible for powering it. If the radiator’s fan motor has failed, the radiator won’t turn on when it needs to. Unfortunately, this can be difficult to diagnose on your own so see a mechanic for this one.^{[2]
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- The fix: A mechanic will test the radiator motor and replace it if necessary.
- The cost: A new radiator fan motor may cost $500-750. A big chunk of the cost here is the part itself, since radiator fans aren’t universal or interchangeable.
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Faulty fan relay The fan relay is a switch that turns on when the fan is told to turn on by the radiator fan switch and/or ECM (engine control module). Basically, the relay closes the circuit necessary for the voltage to reach the fan motor. If the relay is stuck or damaged, the radiator fan won’t be able to turn.^{[3]
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- Cooling fans usually have their own relays that, in many cases, are not shared on the same circuit as the starter relay.
- Just FYI, a bad fan relay can also cause a radiator fan to keep running even when it shouldn’t be. If you ever encounter a fan that won’t turn off, it’s probably the relay.
- The fix: The relay needs to be replaced. See a mechanic to have the relay inspected and replaced.
- The cost: You’ll probably spend $150-300 on a new fan relay.
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Bad ECM Also known as an engine control unit (ECU), the engine control module (ECM) is basically your vehicle’s computer. It monitors the engine and transmission so that your vehicle knows if there’s something wrong. It also sends user inputs to the relevant systems so that your car operates the way you expect it to. If the ECM has an issue communicating with the radiator fan, it may not work as intended. The electronic switch that turns the fan on could be to blame instead.^{[4]
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- The fix: The ECM is a relatively complex system, so see a professional mechanic to have it inspected. It either needs to be repaired or replaced.
- The cost: It depends on what the primary issue is. If it’s just a minor repair, it may cost $200-500. If the entire ECM needs to be replaced, expect to spend around $800 on a new unit.
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Failed fan switch The fan switch is a small metal valve that pops on or off whenever the ECM tells the fan to turn on. If the ECM is fine but the radiator fan still won’t move, it could be a sign the switch itself is bad.^{[5]
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- The fix: See a mechanic to have the switch located, the coolant drained, and the switch replaced.
- The cost: Expect to spend anywhere from $150 to $900 on a new radiator fan switch depending on how hard the switch is to locate and how much work is involved.
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Physical damage to the fan The radiator fan sits behind the grill on the front of your vehicle (either behind the radiator fins or in front of them). When you drive, all kinds of rocks, bugs, dirt, and dust kicks up into your radiator. If something hits your radiator fan, it could damage the fan itself and prevent it from kicking on when it’s needed.
- The fix: It’ll likely be easier for a mechanic to replace the entire fan unit versus repairing the damaged fan.
- The cost: This can cost anywhere from $100-500 depending on how hard the fan is to access and how complex the make and model’s radiator fan is.
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Damaged wiring As a vehicle component that requires a fuse, there’s a wire running from the fan to the fuse box somewhere in your vehicle. If a squirrel or rat has decided to nibble on that wire or it has simply degraded over time, it could keep your radiator fan from operating correctly.^{[6]
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- The fix: The wire needs to be replaced. See a mechanic to have them run a new line from the fuse box to the radiator fan.
- The cost: Expect to spend $50-200 on a new wiring setup for a radiator fan.

Section 2 of 5:

Signs the Radiator Fan Isn’t Working

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1
Engine overheating The radiator and radiator fan are responsible for absorbing all of the heat from your engine (via coolant) and blowing it away from your vehicle. So, if your engine begins to overheat, it’s a big sign something could be going on with either your radiator or radiator fan.^{[7]
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- If the engine starts to run too hot, an emergency temperature warning will pop on. It looks like a little thermostat with two waves underneath. If the engine continues to run hot, you may see steam coming from the engine, smell something burning, or hear thumping noises.
- If you notice overheating issues, start by checking your coolant. A coolant leak or old coolant are much more likely causes of engine overheating than a bad radiator or radiator fan.
The radiator fan isn’t necessary when you’re driving at higher speeds, so it usually only kicks on when you’re driving at a lower speed. As a result, it’s almost certainly a bad radiator fan triggering the overheating if the overheating occurs when you drive at low speeds and dissipates a bit when you’re going faster.^{[8]
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Fan not spinning at idle Some radiator fans sit on the inside of the radiator (to push air out), while others sit in front of the radiator (to pull air out). If your fan is on the front or your radiator fins aren’t very thick, you may be able to see the radiator fan from inside the grill. Since the radiator fan only kicks on at idle or low speeds, you may be able to see if the radiator fan is working by just turning the car on and monitoring the fan.^{[9]
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- If the fan never kicks on after the engine has reached its normal idling temperature, the radiator fan is probably not working correctly.
- This may not work if it’s under 60–70 °F (16–21 °C) outside. It just may never get hot enough to force the radiator fan on.

Section 3 of 5:

How does the radiator fan work?

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The radiator fan helps cool the coolant when driving at low speeds. When you’re driving at high speeds, there’s a lot of air flowing in through your car’s grill. That air helps pull the heat off of the radiator and cool your vehicle. But at lower speeds there’s no airflow. To help keep heat from building up in the engine bay, the radiator fan turns on at low speeds to provide additional help.^{[10]
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- The radiator fan is especially helpful in hotter weather when the engine gets hot fast at lower speeds. If you live in a really cold climate, you may never even notice the radiator fan isn’t working.

Section 4 of 5:

Can you test a radiator fan motor?

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Yes, but it’s dangerous and probably best left to a professional. To test the radiator fan motor, you likely must start by disassembling your radiator to access the motor. Then, connect 12-volt jumper cables to the terminals inside of the motor housing and jump it to see if the fan moves. If it does, the motor is fine. If it doesn’t, the motor is dead.
- A note on safety: You must wear protective eyewear and heat-resistant gloves when working on your radiator. Never unscrew the radiator cap or decouple a radiator junction unless the engine is completely cold.^{[11]
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- Testing electrical components is difficult for non-gearheads. There are a lot of wires and fuses in a vehicle, so if you don’t know what you’re looking for it’s probably best to let a professional do this.

Section 5 of 5:

Is it safe to drive without a radiator fan?

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Yes, but only so long as your engine doesn’t overheat. The radiator fan turns off automatically when it’s not needed (which is actually most of the time if you don’t live in a hot climate). If the radiator fan isn’t working but it’s not causing your engine to overheat, you’re good to drive. However, if you notice any kind of serious overheating risks, do not drive. You may destroy your engine or start a car fire.^{[12]
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- Your car should be safe so long as you pull over and shut the engine off when the temperature gauge pops on (or the dial enters the yellow/red). If you keep driving to the point that you see smoke, smell burning, or hear noises though, you could be do serious damage to your vehicle.

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Tips

Some people mistake the radiator fan for the cooling fan. The cooling fan is responsible for extracting cold air from the coolant and blowing it into the cabin when the AC is on. If you don’t have any cold air when you turn the AC on, the problem isn’t your radiator fan—it’s the cooling fan.

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In a small number of car models, it’s possible that a bad coolant temperature sensor could keep a radiator fan from kicking on. However, your engine would start smoking and overheating way before you notice the radiator fan isn’t working if the coolant sensor is bad.

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