Can A Bad Alternator Cause Overheating [Why+ How To Fix] 

If you find your car’s alternator and engine both being hot at the same time, you may think that the alternator is causing the issue. So, can a bad alternator cause overheating in your car’s engine?

The short answer is that it’s highly unlikely. In most cases, a faulty or bad alternator won’t make your car’s engine hot. But never say never as it can happen in rare cases.

can a bad alternator cause overheating

We’ll explain how it works with the necessary details in this guide. Without further ado, let’s dive in!

Can A Bad Alternator Cause Overheating [Explained A-Z]

A basic understanding of how the alternator works will help you realize why it’s rare for the alternator to cause overheating of the car.

An alternator is a device that’s responsible for providing power to all the electrical connections and devices when your vehicle is running.

bad alternator

When the car is off, this job is done by the battery. In addition to that, the alternator also charges the battery when you drive your car. When you start your vehicle, the crankshaft rotates, and that causes the drive belt to rotate.

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

So, that’s why there’s one in a million chance of a bad alternator making your engine overheat. However, remember the rare case we talked about? Sometimes, the radiator fans are powered by the alternator.

When the alternator gets extremely weak, it won’t be able to fulfill the demands of the radiator fan. So, the cooling system of the engine will be compromised. But even that won’t make a significant impact in overheating the car.

Thus, an alternator having a major hand in overeating your car is next to impossible. What’s much more likely is that the alternator will get hot independently on its own.

It often happens in bad alternators. In fact, even normal and functional alternators get hot when you drive your car. So, if you catch your alternator being hot after you’ve driven your car for a while, there’s nothing to worry about.

Why Does The Alternator Become Hot

Now you know that it’s a part of the normal operation of an alternator to become hot. But if it gets too hot or you see other warning signs that indicate you have a bad alternator, that’s not okay.

There are many things that can make your alternator go bad. If you suspect that the faulty alternator is causing your car to overheat, it’ll most likely be the serpentine belt that’s causing the issue.

If you put the serpentine belt in the wrong way, or there’s not enough tension in it, your alternator can easily be overheated. All the power of the alternator comes from mechanical energy. So, when there’s something wrong with it, the alternator can be hot.

serpentine belt

A bad serpentine belt can also make the car’s engine overrated. So, while you may suspect a bad alternator to be the issue here, in reality, there’s a strong chance that the serpentine belt is causing the issue.

Make sure the serpentine belt is in good condition and there’s proper tension on it. Check out our guide on why the serpentine belt keeps slipping if you’re facing this issue and learn how you can solve it.

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

Go to our guide on brand new alternator overheating if you want to learn more about it. We’ve discussed the major reasons behind it and how you can fix them in that guide.

What Are The Symptoms Of A Bad Alternator?

You came into this guide with the assumption that you have a bad alternator. But you may not have a bad alternator in the first place and there could be some other issues that are causing your car to overheat.

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

1. Lights Getting Dim Or Too Bright

As the alternator is responsible for providing power to the electrical components in your car, the first sign of it going bad is seeing issues with the lights in your car.

 lights getting dim or too bright

If the headlights or interior lights in your car suddenly get too bright or dim, it’s a tell-tale sign of a bad alternator. Your dash lights may completely stop working because of a bad alternator.

Along with that, the radio, speedometer, tachometer, and other electrical parts can stop functioning due to a faulty alternator. The lights can also flicker and signal issues with the alternator. Usually, the main reason behind it is when the alternator fails to supply electricity at a consistent voltage.

2. Dead Battery

The battery in your car powers the electrical components when the car is not running. But in doing so, it loses its charge. So, the alternator does the job of charging the battery when you start and drive your vehicle.

dead battery

When an alternator fails to do its job, it won’t charge the battery properly and you can end up with a dead battery. So, if your car’s battery goes dead abruptly, it’s a strong sign of a malfunctioning alternator.

3. Strange Noises

The engine makes a lot of noise when you operate a car and that’s normal. But unfortunately, if you hear a grinding or whining noise from your alternator, it indicates that the alternator is starting to wear out.

More specifically, it’s the alternator bearings that are going bad. The alternator pulley spins two to three times faster than the crankshaft pulley on average to generate the power your car requires.

But when it’s not aligned properly with the drive belt, it can also cause this grinding noise.

The most likely outcome of this symptom is that the bearing will get sized at one point and the alternator will stop working altogether. In that case, you’ll be left with no choice but to replace the alternator.

4. Unpleasant Smell

As you’d know by now, the alternator is under constant tension due to the serpentine belt. If you notice weird smells like burning rubbers or electrical fires, it indicates issues with the alternator.

The burning rubber smell points to a worn-out drive belt that needs to be replaced. But the smell of electrical wire represents the wiring of the alternator getting damaged.

5. Warning Light

If your car isn’t too old and was made in the last decade or so, it’ll most likely be equipped with a dash light to indicate a bad alternator. You’ll see warnings on your dash that say “ALT” or “GEN” where the former refers to the alternator and the latter refers to the generator.

alternator warning light

In older vehicles, the check engine light may get triggered because of a bad alternator. Sometimes, the battery symbol may also come on and that indicates an issue with the electrical system of the car. It could mean either the battery or the alternator or both of them have gone bad.

When your alternator is healthy, it gives a voltage output in the range of 13V and 14.5V. If it goes out of range, the electrical system gets messed up and that triggers the warning light.

6. Stalling Or Difficulty Starting

When your alternator fails to charge the battery, you’d have trouble starting your vehicle. That’s because the initial power required to start the car is provided by the battery.

And when the alternator fails to charge the battery, it no longer has the power to start the vehicle without any issues. However, the engine stalling issue can be caused by other problems as well and it’s no conclusive evidence of having a bad alternator.

7. Bad Drive Belt

In all honesty, this issue is the other way around. You may face problems even with a good alternator when you have a bad drive belt. The car overheating issue can also point to a bad belt.

The belt powers important components alongside the alternator like the water pump and AC compressor. When it goes bad, the water pump doesn’t work properly and that can increase the temperature of the car’s engine.

It’s incredibly easy to check the drive belt for damage. So, check it for wear and tear with a flashlight. Make sure you rule out a bad drive belt before you make up your mind that you have a bad alternator.

How To Test An Alternator

Even if the symptoms point to a bad alternator, you can never be fully sure if that’s the case until you get your alternator tested. It’s the only conclusive way to find out whether you have a bad alternator on not.

test an alternator

The good news is that you can easily do this test on your own if you have a good-quality multimeter. Follow these steps to do the test on your alternator and determine if it’s good or bad:

  • Attach the red probe of the digital multimer to the positive terminal of the battery.
  • Connect the black probe of the digital multimer to the negative terminal of the battery.
  • Turn the selector switch in the multimeter to DC voltage.
  • Start the engine and leave it idle.
  • Note the readings on the multimeter.

As you already know, a good alternator provides an output voltage between 13V and 14.5V. Ideally, it’ll be in the range of 13.8V to 14.2V. If the alternator’s output voltage is outside the acceptable range, it means you have a bad alternator and you’ll have to replace it.

Why Does The Car Become Hot

As you can see, it’s safe to say that the alternator wouldn’t likely be the main reason behind an overheating car. So, you may be interested in finding out what actually causes your car to overheat. Apart from a bad drive belt, the most common reasons behind it are:

i. Coolant Leaks

The coolant in your car is supposed to keep the temperature of the engine down. If the coolant gets leaked due to worn-out hoses, radiators, or clamps, your car will get overheated.

coolant leaks

Moreover, the spillover can damage certain components of the engine. If you find coolant leaking from your car, you should immediately locate its source and fix it to prevent further damage to your engine.

ii. Failing Water Pump

The job of the water pump is to transfer the coolant from the radiator to all the necessary engine components. When the water pump fails to circulate the coolant properly, the car will start to overheat.

failing water pump

When the water pump goes bad, you should replace it as soon as you can. On average, a water pump lasts up to 100,000 miles.

iii. Blown Head Gasket

A blown head gasket is one of the worst reasons and consequences of an overheating engine. You can do a compression test to find out whether you have a blown head gasket.

blown head gasket

You’ll usually pour a blue liquid into a tube to test the head gasket. If it turns yellow, you have a bad head gasket. If it stays blue, then the head gasket is fine.

It may not make financial sense to replace the head gasket as it costs a lot. Decide wisely as there can be additional repair costs along with it.


Why is my car overheating after replacing the alternator?

Not putting the serpentine belt correctly is the main reason why your car overheats after replacing the alternator. Make sure that the serpentine belt is in good condition, put in the right direction, and has proper tension.

Can hot weather affect the alternator?

Yes, the weather conditions in an area have an impact on major car components including the alternator. Excessive heat increases the electrical energy resistance which makes the alternator work harder and causes it to eventually go bad.

Can a bad alternator cause a coolant leak?

An alternator doesn’t affect the cooling system of your car at all. Therefore, it can never cause a coolant leak. However, coolant leaking and getting into the alternator can damage the alternator.

Can cold weather affect the alternator?

Extremely cold or freezing conditions will make it difficult for the alternator to spin and can even damage the alternator bearings. Sometimes, you may even fail to start the engine because of this cold weather.

How much does it cost to replace an alternator?

Depending on the quality of the alternator required to power your car’s electrical system, you’ll most likely be spending in the range of $200 – $1200 to get your alternator replaced.


Can a bad alternator cause overheating? Hopefully, now you know the answer after completing this guide. Alternators won’t normally have an impact in overheating the cars as they’re only responsible for powering the different electrical parts in the car.

If you have a vehicle that’s overheating, it’s most likely caused by other issues like a bad drive belt, coolant leaks, and so on. Diagnose your car carefully and find out what’s causing the problem. Comment below if you have any questions about alternators.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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