7 Common Causes of Overheating in Car Alternators (+Fixes)

Car alternators can work faultlessly for many years.

Occasionally, though, you may have a scary case of a burnt smell and damage to the alternator from overheating.

It is still worthwhile knowing the signs and causes of overheating in a car alternator so that you can recognize and prevent them from happening whenever possible.

In this post, I cover signs that your alternator is overheating, the reasons why it might overheat, and how you may be able to prevent overheating and damage to the alternator.


Is It Normal for an Alternator to Heat Up

It is normal for the car alternator to become hot as the car engine runs.

The heat in the car alternator comes from a combination of the friction in the bearings and belt drive of the alternator plus the resistance to the current flow through its windings and diodes.

As the demand for electric power in the car increases as car accessories are switched on, so does the current flow and temperature in the alternator.

Fortunately, the alternator has an inbuilt fan that runs and cools it down. It also has inbuilt circuitry that reduces current output in cases of excessive heating of the alternator.

How Hot Should an Alternator Get?

Alternators can get extremely hot to touch during the normal operation of the car.

In fact, touching the casing of one after the engine has been running for some time can cause injury from burns.

While an alternator may be able to withstand temperatures during its normal operation, if it is subjected to excessive temperatures for a long time, the alternator can fail prematurely.

Signs of an Overheating Car Alternator

You may be able to tell that your alternator is overheating when you:

  • Notice a burning smell from the hood where the alternator is installed
  • A burnt or folded label on the side of the alternator. When the alternator overheats, this tag may be discoloured, and folded.
  • You may notice that the alternator shaft color has changed to another darker shade because of the excessive heat.
  • In severe cases, you may have smoke coming from the alternator.

You may also want to read: bad battery vs. bad alternator

7 Reasons Why Your Alternator Is Overheating

Your car’s alternator may overheat for various reasons:

#1. Bad wiring

A bad poor ground or a poor connection in the car’s charging circuit can restrict the current flow and affect a battery’s ability to charge properly.

This in turn makes the alternator work unusually hard and can result in overheating and possibly early failure of the alternator.

Secondly, bad wire connections combined with high current draw from the alternator can cause smoldering and burning at the wire connections.

#2. Poor air circulation around the alternator

If there is no free flow of air around the alternator because of mud, or other debris covering the alternator, its internal temperature can build up rapidly causing damage to it.

This is more likely to happen if the alternator is producing large currents which result in a higher temperature rise.

#3. Damaged bearings

Does the alternator make an abnormal noise as it runs? Worn-out bearings can restrict the smooth running of an alternator increasing the heat build-up to levels that are bad for the alternator.

#4. Damaged battery

A damaged battery, for example, a battery with a damaged cell can also cause the alternator to overwork.

This causes a large current flow as it attempts to charge the battery for an unusually long time leading to damage and overheating of the alternator.

So, if the battery is damaged, replace it right away. Attempting to charge it using the alternator can cause the alternator to fail too.

You may also want to check out: How often to replace a car battery

#5. Poorly tensioned belts

Are the belts coupling the alternator to the car engine properly tensioned?

This can be an issue if you have just fitted a new belt.

A poorly tensioned belt affects the alternator fan speed. It may not be able to cool the alternator well, causing excessive build of heat in the alternator.

#6. Poor quality alternator or an undersized replacement

Poor quality alternators can overheat. An undersized alternator will also likely overheat from generating more power than it is designed to. Has your original alternator failed?

Make sure to replace it with one recommended by the car manufacturer.

#7. Faulty alternator

An alternator with shorted windings, diodes or even the regulator can cause overheating of the alternator.

You may want to read: 2 Easy ways to check if the alternator is draining the car battery

How to Fix an Overheating Alternator

You can prevent your alternator from overheating and damage by:

  • Check that the alternator vents are clear of any mud or other debris that may block airflow leading to overheating
  • Replacing damaged batteries promptly.
  • If you make any changes to the car’s electrical system, make sure that the wiring is fixed as recommended to avoid wiring faults that can damage the alternator.
  • If you change the belt, make sure it is fitted and tensioned properly
  • If replacing an alternator, get a good quality one recommended by the car manufacturer. Alternators also have an inbuilt mechanism to reduce the heating

Related questions

Why Does the Alternator Get Really Hot Even when The Engine Is Off?

If the car alternator is hot to touch even when the engine is off, this can point to a fault in the alternator, probably a short-circuit in the windings, diodes, or regulator.

This type of fault can cause a current draw from the battery and usually leads to a drained battery.

To fix this, have your alternator and car’s wiring checked by a qualified auto technician

Final Thoughts

An overheating alternator can be scary, particularly when there is a burning smell or smoke from under the hood.

There are several causes of overheating alternators – damaged battery, bad wiring, undersized alternators, loose or poorly tensioned belts, or even an alternator whose vents are blocked with mud.

Knowing the cause of overheating can hopefully help in preventing them in the first instance or a repeat of the same.

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