A Bad Alternator Can Cause You To Overheat [Why + How To Fix It] (2023)

If you find your car's alternator and engine are hot at the same time, you may think that the alternator is causing the problem. So, can a faulty alternator cause your car's engine to overheat?

The short answer is that it is highly unlikely. In most cases, a bad or faulty alternator will not warm up your car's engine. But never say never, this can happen on rare occasions.

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We explain how this works in the necessary detail in this guide. Without further ado, let's dive in!

Table of contents

  • Can a defective alternator lead to overheating? [Explained from A to Z]
  • Why does the alternator get hot?
  • What are the symptoms of a defective alternator?
  • 1. Lights are dim or too bright
  • 2. Battery empty
  • 3. Strange noises
  • 4. Unpleasant smell
  • 5. Warning light
  • 6. Stalling or starting difficulties
  • 7. Defective drive belt
  • How to test an alternator
  • Why is the car getting warm?
  • I. coolant leaks
  • ii. defective water pump
  • iii. defective cylinder head gasket
  • Frequently asked questions:
  • Why is my car overheating after replacing the alternator?
  • Can hot weather affect the alternator?
  • Can a faulty alternator cause a coolant leak?
  • Can cold weather affect the alternator?
  • How much does it cost to replace an alternator?
  • Diploma

Can a defective alternator lead to overheating? [Explained from A to Z]

A basic understanding of how the alternator works will help you understand why it is rare for a car's alternator to overheat.

An alternator is a device responsible for powering all electrical connections and devices when the vehicle is running.

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When the car is switched off, this task is taken over by the battery. In addition, the alternator also charges the battery when you drive the car. When you start the vehicle, the crankshaft rotates and this causes the drive belt to rotate.

The drive belt is connected to the alternator. The alternator converts the mechanical energy generated by the movement of the drive belt into electrical energy. As you can see, the alternator depends on the car's engine. It's not the other way around.

Therefore, there is a one in a million chance that a bad alternator will overheat your engine. However, remember that rare case we talked about? Sometimes radiator fans are driven by the alternator.

When the alternator becomes extremely weak, it cannot meet the needs of the radiator fan. Then the engine cooling system will be affected. But even this does not significantly affect the overheating of the car.

Therefore, it is almost impossible for an alternator to play a major role in charging your car. It is much more likely that the alternator will warm up on its own.

It often happens with defective alternators. In fact, even normally working alternators get hot when you drive your car. So if you find your alternator is hot after driving for a while, don't worry.

Why does the alternator get hot?

Now you know that normal operation of an alternator will cause it to get hot. But if it gets too hot or you see other warning signs that the alternator is bad, you're wrong.

There are many things that can cause your alternator to fail. If you suspect that the faulty alternator is overheating the car, it is most likely the V-belt that is causing the problem.

If you position the V-belt incorrectly or have too little tension, your alternator can easily overheat. The entire power of the alternator comes from mechanical energy. So if something is wrong, the alternator could be hot.

A bad V-belt can also put a strain on your car's engine. While you might suspect that the problem is a bad alternator, in reality there is a very good chance that the serpentine belt is causing the problem.

Make sure the serpentine belt is in good condition and has the correct tension. Check out our guidewhy does the V-belt keep slipping?if you are facing this problem and know how to solve it.

Aside from the drive belt, there are many other things that can cause your alternator to overheat. A bad voltage regulator and dead battery are also some of the most common reasons that lead to alternator overheating.

Access our guideNew alternator overheatedif you want more information about it. We discuss the main reasons behind it and how to fix it in this guide.

What are the symptoms of a defective alternator?

You came to this guide assuming you have a bad alternator. But you may not have a bad alternator at all, and there could be other issues causing your car to overheat.

If you know the most common warning signs of a bad alternator and notice them in your car, you can be pretty sure that you have a bad alternator.So here are the symptoms of a bad alternator.:

1.The lights are dim or too bright

Since the alternator is responsible for powering the car's electrical components, problems with your car's headlights are the first sign that it is failing.

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If your car's headlights or interior lights suddenly become too bright or too dim, it's a telltale sign of a bad alternator. The dashboard lighting can fail completely due to a defective alternator.

Also, the radio, speedometer, tachometer and other electrical parts can stop working due to a faulty alternator. The lights can also flicker, indicating problems with the alternator. Usually the main reason for this is that the alternator cannot supply current with a constant voltage.

2.empty battery

Your car battery powers electrical components when the car is not running. However, it loses its charge. The alternator then takes over the task of charging the battery when you start and drive the vehicle.

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When an alternator isn't doing its job, it's not charging the battery properly and you could end up with a dead battery. Therefore, when your car battery suddenly dies, it is a strong sign that the alternator is not working properly.

3.strange noises

The engine makes a lot of noise when driving and this is normal. But unfortunately, if you hear a squeak or squeak from the alternator, then this indicates that the alternator is starting to wear out.

More specifically, it is the alternator bearings that are failing. The alternator pulley rotates, on average, two to three times faster than the crankshaft pulley to produce the power your car needs.

But if it's not properly aligned with the drive belt, it can also cause that grinding noise.

The most likely result of this symptom is that the bearing will rise at one point and the alternator will stop working entirely. In this case, you have no choice but to replace the alternator.

4.unpleasant smell

As you may already know, the alternator is under constant tension from the V-belt. If you notice strange smells like burnt tires or electrical fires, this indicates problems with the alternator.

A burnt rubber smell indicates a worn drive belt that needs to be replaced. But the smell of electrical wire indicates damage to the alternator wiring.


Unless your car is very old and was manufactured within the last decade, it is likely equipped with a dashboard light that indicates a faulty alternator. On your dashboard you will see notices labeled 'ALT' or 'GEN', the first relating to the alternator and the second to the alternator.

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On older vehicles, the check engine light may come on due to a bad alternator. Sometimes the battery icon will also illuminate, indicating a problem with the vehicle's electrical system. This could mean that the battery or the alternator or both are defective.

If your alternator is in good condition it will produce a voltage in the range of 13V to 14.5V. If it is out of range then the electrical system is faulty and this will activate the warning light.

6.Stopping or difficult to start

If the alternator is not charging the battery, you will have trouble starting your vehicle. The battery provides the initial energy required to start the car.

And if the alternator doesn't charge the battery, it won't have the power to start the vehicle smoothly. However, a sticking problem can also be caused by other problems and is not conclusive evidence of a bad alternator.

7.defective drive belt

In all honesty, this problem is backwards. Even with a good alternator, a defective drive belt can cause problems. A car overheating problem can also indicate a faulty belt.

Together with the alternator, the belt drives important components such as the water pump and the air conditioning compressor. When things get bad, the water pump isn't working properly and that can increase the temperature of the car's engine.

It's incredibly easycheck the drive beltCheck for damage, i.e. wear, with a flashlight. Be sure to rule out a bad drive belt before deciding you have a bad alternator.

How to test an alternator

Even if the symptoms point to a bad alternator, you can never be completely sure until you test it. This is the only way to determine whether you have a defective alternator.

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The good news is that you can easily do this test yourself if you have a good quality multimeter. Follow these steps to test your alternator to determine if it's good or bad:

  • Connect the red test lead of the digital multimeter to the positive terminal of the battery.
  • Connect the black test lead of the digital multimeter to the negative battery post.
  • Set the multimeter's selector switch to DC voltage.
  • Start the engine and let it idle.
  • Observe the readings on the multimeter.

As you already know, a good alternator will provide an output voltage between 13V and 14.5V. Ideally it should be in the 13.8V to 14.2V range. If your alternator output voltage is outside the acceptable range, it means you have a bad alternator and need to replace it.

Why is the car getting warm?

As you can see, it's safe to say that the alternator is probably not the main reason your car is overheating. Therefore, you may be interested to know what really causes your car to overheat. Aside from a bad drive belt, the most common reasons for this are:

EU.coolant leaks

Your car's coolant is designed to keep the engine temperature down. If coolant leaks from worn hoses, radiators or clamps, your car will overheat.

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In addition, spillage can damage certain engine components. If you find a coolant leak in your car, immediately locate the source and repair it to prevent further engine damage.

ii.defective water pump

The job of the water pump is to move coolant from the radiator to all necessary engine components. If the water pump is not circulating the coolant properly, the car will start to overheat.

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If the water pump fails, you need to replace it as soon as possible. On average, a water pump lasts up to 100,000 miles.

iii.defective cylinder head gasket

A blown head gasket is one of the worst causes and consequences of engine overheating. You can determine if the head gasket has blown by doing a compression test.

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Usually you pour blue liquid into a tube to test the head gasket. If it turns yellow, you have a bad head gasket. If it turns blue, the head gasket is good.

It may not make financial senseReplace head gasketsince it costs a lot. Decide wisely as there may be additional repair costs.

frequently asked questions:

Why is my car overheating after replacing the alternator?

Incorrect positioning of the V-ribbed belt is the main reason why your car overheats after replacing the alternator. Make sure the serpentine belt is in good condition, routed in the correct direction, and has the correct tension.

Can hot weather affect the alternator?

Yes, the weather conditions in an area affect the main components of the car, including the alternator. Excessive heat increases the resistance of the electrical energy, causing the alternator to work harder and eventually to fail.

Can a faulty alternator cause a coolant leak?

An alternator does not affect your car's cooling system at all. Therefore, there can never be a coolant leak. However, coolant escaping and penetrating the alternator can damage the alternator.

Can cold weather affect the alternator?

Extreme cold or icy conditions will make the alternator difficult to rotate and may even damage the alternator bearings. Sometimes the engine won't even start due to this cold weather.

How much does it cost to replace an alternator?

Depending on the quality of the alternator needed to power your car's electrical system, you will likely spend anywhere from $200 to $1200 to replace your alternator.


Can a defective alternator lead to overheating? Hopefully you now know the answer after completing this guide. Alternators usually have no effect on car overheating as they are only responsible for powering the various electrical parts of the car.

If your vehicle is overheating, it is most likely due to other issues like a bad drive belt, coolant leaks, etc. Diagnose your car carefully and find out what is causing the problem. Please comment below if you have any questions about alternators.

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