Brand New Alternator Overheating [Why+ How To Fix]

The number one reason behind a brand new alternator overheating is a faulty voltage regulator. If you’re facing this issue, you’ll have to replace the regulator.

However, it’s not the only potential problem behind this issue. Some other common reasons that can cause the alternator to overheat are:

brand new alternator overheating
  • Dirty Battery Terminals Or Dead Battery
  • Wrong Alternator
  • Cooling Issues
  • Bad Drive Belt
  • Wiring Issues
  • Faulty Diode

We’ll discuss each of these problems in detail. Not only that, but you’ll also get to learn the solutions and fix each of the issues. So, let’s dive right in!

Brand New Alternator Overheating [7 Easy Fixes]

Before diving deep into the main reasons behind an overheating alternator, there’s something you should be aware of. Remember that it’s normal for the alternator to get hot to some degree after driving your car.

alternator overheating

Don’t sweat it if your new alternator gets hot in those instances. All the engine parts get hot when driving and you’ll feel that everything is hot when you touch the components.

In the example above, the alternator has reached a temperature of over 160 degrees. And that’s fine after driving. The amount that the alternator sits on also makes it hot.

If you’ve realized that, then relax and give the alternator some time to cool down. You don’t have to take any steps here as there’s no real problem.

However, it doesn’t mean that it’s okay for the alternator to get hot when the car is off and has had a good amount of rest after driving. It’s not normal and needs to be diagnosed.

Besides that, seeing warning lights on your dash, a grinding sound from the alternator, or a burning smell from the engine are all terrible signs. You need to diagnose these issues and fix them immediately.

If you don’t take corrective actions as early as possible, the entire electric system in your car can get damaged. Now that you have a clear understanding of when a hot alternator actually means trouble, let’s get into it.

Note: You can also read our guide on car battery has voltage but no amps.

1. Faulty Voltage Regulator

The alternator recharges the battery and runs the entire electrical system in your car when you drive the vehicle. As it converts mechanical energy into electrical current, it produces a lot of energy.

faulty voltage regulator

But the battery doesn’t always need that much power. So, there’s a voltage regulator that helps manage the output of the alternator and prevents the battery from getting overcharged.

While the alternator can easily produce more than 13.5 volts, the battery can handle only 12 volts. That’s why the voltage regulator is so important. When it goes bad, it can cause the alternator to produce too much electricity and it can get overheated.


You can start by inspecting the voltage regulator with a multimeter if you can locate it. Unfortunately, the location of the voltage regulator can vary depending on the vehicle. Sometimes, it can be placed in alternator housing. For other vehicles, it can also be placed next to the alternator.

If you’re able to do the test yourself and find faulty readings, you’ll have to replace the voltage regulator. It’s not safe to keep driving with a faulty voltage regulator as it can overcharge the battery and damage the other components of the electrical system.

You need to get your car inspected by a mechanic if you can’t check the voltage regulator on your own and get it replaced. The voltage regulator itself will cost between $50 – $150 depending on your car.

That’s all it’ll take to replace it on your own. But if you the help of a mechanic, you can expect that it’ll cost an additional $150 – $250 in labor charges. Once it’s replaced after a proper diagnosis, the alternator will stop overheating.

2. Dirty Battery Terminals Or Dead Battery

The battery and the alternator have a symbiotic relationship and they both need to be working correctly to supply power to the electrical system in a car. If you have a weak or dirty battery, the alternator will try to make up for it and that can cause it to overheat.

dirty battery terminals

Start by checking the terminals of the car battery. If there are no issues there and you see no visible corrosion, you may have a bad battery. Keep in mind that even if one out of the six cells of the battery goes bad, it can cause the alternator to overwork.

Some symptoms of a bad battery are:

  • The battery light on the dashboard turns on.
  • The engine cranks slowly.
  • Difficulty starting the vehicle.
  • The interior lights get dim.


If the terminals of the battery are corroded, you need to clean them. Make sure you turn the engine off before you disconnect the battery. It’s a good idea to wear safety goggles when cleaning the battery terminals to prevent corrosion from getting into your eyes.

Here are the steps to do it:

  • Disconnect the negative terminal first (black). Then, remove the positive terminal (red).
  • Use the solution of your choice to clean the terminals. You can use a paste of baking soda and hot water. Or you can also use battery terminal cleaner.
  • Spray the solution on the battery terminals and clean them using a wired brush.
  • When the corrosion is clear, wipe down the terminals with a piece of cloth.

That’s it. Make sure you wait for the terminals to dry before connecting the battery again. To keep the terminals from getting corroded in the future, you can apply some dielectric grease to them.

It’ll slow down the corrosion by a great deal even if it doesn’t completely stop it. Connect the positive terminal first and then, the negative one. There’s also another chemical called battery terminal protector that you can apply to the terminals before starting your car.

If you don’t have a corroded battery and have a bad battery instead, you need to replace it. Make sure you choose the right battery for your vehicle and that’ll keep the alternator from overheating.

3. Wrong Alternator

It’s a sore sight to see a new alternator malfunctioning but sometimes, you’ll just be unlucky. The alternator you purchased may have a manufacturing defect such as shorted diodes, windings, and regulator.

wrong alternator

Hopefully, you’re at least covered by warranty if you bought a bad alternator. Besides that, getting a poor-quality alternator on one that’s undersized to meet the needs of your vehicle can also easily overheat.


In both cases, you’ll have to replace the alternator again. Make sure you get the right alternator as per the recommendations of your car manufacturer. When you do that, it’ll run smoothly as long as there are no other issues.

4. Cooling Issues

The alternator in most vehicles is air-cooled even though top brands like BMW are switching to liquid cooling systems. As the alternator produces a lot of heat to generate electricity, the alternator fan would draw air from the outside and gets rid of the heat.

alternator cooling fan

But if mud or any other form of debris covers the alternator, it won’t be able to get rid of the heat. The temperature inside will keep rising and eventually, it’ll overheat. The alternator cooling fan can also go bad which can cause the internal temperature to rise.


If the alternator is covered by debris, you’re in for an easy fix. Just remove the dirt covering it and you’re good to go. It’s rare for the fan to malfunction in new alternators.

But if that happened, you’ll have to replace the fan. In some cases, you’ll have to replace the alternator as you won’t find the fan as a separate unit.

5. Bad Drive Belt

When the car starts using the initial burst of power provided by the battery, the crankshaft gets rotated. It’s connected to the alternator by the drive belt. For the alternator to function properly, the drive belt needs to have proper tension. 

checking the drive belt

Without the right tension of the drive belt, the cooling fan of the alternator won’t work properly. Either poor installation of the belt can cause this issue or the belt itself is bad.


If the tension of the belt is incorrect but the belt is fine, it needs to be readjusted. Get a torch and look under the belt to see if there are any significant signs of wear and tear. If there’s no damage, then it’s most likely poor tension that caused this issue.

Attach a tension gauge to the longest belt span and pull it to measure the tension. Compare it with the recommended readings in your vehicle’s manual. If it doesn’t match the readings, you need to adjust it.

It’s common to face this issue after replacing the drive belt as some mechanics don’t replace it correctly. Follow these steps to adjust the drive belt and make sure it has the right tension:

  • Disconnect both the negative and positive terminals of the battery.
  • Place a pry bar and use it as a lever to apply tension to the belt.
  • Loosen the alternator bolts so that you can adjust the tension on the belt.
  • Wedge the pry bar between the alternator and a strong part of the engine.
  • Pull it in the direction that’ll apply the tension to the belt.

Check the tension again and keep adjusting it if needed. Once you’re happy with it, you can connect the battery again. It should keep your alternator from overheating from there on.

If the belt is cracked, glazed, or torn, it’ll have to be replaced. You’ll have to slide the old belt off the pulleys, put the new one in its place, and adjust the tension on the new belt.

6. Wiring Issues

The next thing you need to inspect if you have an overheating brand-new alternator is the wiring system. The electrical system in your car is connected to the alternator using a series of wires.

When the wires get corroded or damaged, it can make the alternator work harder, get overheated, and eventually, fail. The ground cable of the alternator must also be fitted properly for the alternator to function properly.


Inspect the wiring and see if you can find any issues. As bad wiring causes smoldering and burning at the wire connections, it’ll be pretty easy to detect them. Check the ground cable and make sure it’s nice and tight.

If you come across wiring that’s corroded or even damaged, it’s a good idea to just replace it altogether. Bad wiring can also damage the battery of the car. So, you should fix this issue as soon as you can to avoid further problems.

7. Faulty Alternator Diode

Of all the problems we discussed so far, this is the most unlikely reason for a new alternator to overheat. It’s common in used alternators but it can also happen in new alternators at times.

faulty alternator diode

As you may already know, the alternator produces AC current. But the car needs DC. So, there are a bunch of diodes that send the electrons in a specific direction and cover the AC to DC. This process is called rectification.

When a diode malfunctions, it can easily make the alternator overwork and cause it to overheat. Thankfully, you can easily inspect it if you have a bad diode using a multimeter.

Remember that if you place the red lead on the positive cable and the black lead on the alternator, you’ll get no readings for a functional diode. But if you switch the connections and put the red lead on the alternator and the black lead on the positive cable, you’ll get readings.

If you have a bad diode, you’ll get readings even in the first instance when the red lead of the multimer is placed on the positive cable. You can inspect each diode with this principle and if you get readings on both ends, you can be sure that you have a malfunctioning diode.


If you have a faulty diode, you’ll need to replace it to keep the alternator from overheating. The alternator needs to be disconnected from the car and opened up, the diode needs to be changed, and the alternator needs to be reassembled. Hire a mechanic to do it if you’re not comfortable doing it yourself.


Does a voltage regulator frequently go bad?

How long a voltage regulator varies significantly depending on the vehicle and the environmental conditions. But as a general rule of thumb, you can expect it to last more than 100,000 miles.

How often does a car battery last?

A car battery lasts for around 4-5 years on average. However, you can prolong its life by cleaning the terminals at regular intervals.

What causes an old alternator to overheat?

An old alternator will also overheat for the same reasons we discussed. But one additional thing you need to check is whether the alternator bearings are worn out. When they rub on the metal cover, it generates excessive heat and overheats the alternator.

Does the alternator generate AC or DC?

Initially, the alternator generates AC when it converts mechanical energy into electric current. But as the car needs DC, the current gets converted into DC using a device called a rectifier.


Keep in mind that a brand new alternator overheating can be completely normal at times. It’s common for all engine components to get hot when they’re used and the alternator is no exception.

However, we’ve discussed the potential reasons behind it if your issue is more serious. If this guide helped you in fixing your alternator, let us know how you did it. Comment below if you have any more questions about overheating 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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