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

A car alternator can work reliably for many years for the most part. But, you can never rule out that one exception – such as when it fails every so often because it’s overheating.

What causes an alternator to overheat? What signs show that the alternator is overheating?

Read on to find out why the alternator is overheating, what signs show, and how to stop it from overheating.

Why a Car Alternator may be Overheating?

If the car alternator temperature is excessive, it might be because:

1. The car battery connections are loose and not making good, clean contact. Are the battery positive, negative, or ground connections firmly connected?

Are you able to lift the battery terminal off the post or rotate it from side to side with gentle pressure?

If so, then the battery cable connections are loosely connected.

When battery connections are loose or make poor contact because of corrosion, the current flow to the battery during the charging process is reduced.

It then takes the alternator a longer time to fully charge the battery which leads to overheating.

2. The car battery voltage is extremely low. The charging current from the alternator to the battery is higher when the battery is discharged.

Additionally, restoring to full charge takes a longer time.

The combination of high charging currents and long duration to charge can also lead to overheating of the alternator,

If the battery voltage is low, use a car battery charger to charge it first before hooking it up to an alternator.

3. The alternator vents are blocked or there is poor airflow around the alternator. Is the inbuilt cooling fan running smoothly?

Poor airflow around the alternator because the vents are blocked or the fan is not rotating leads to a buildup of heat in the alternator and eventually overheating.

Inspect the vents (when the engine is off) and the alternator is cooled down and remove any mud, or dust that may have caked on the alternator so air is flowing freely into the alternator so that it runs cooler.

4. The Battery is faulty

A faulty battery such as one with an internal shot may be the reason that the alternator is overheating.

Such a battery draws a higher current from the alternator, overworking it which then leads to overheating.

Replace a damaged battery right away (once confirmed faulty – can take it to a reputable auto repair shop) if it shows signs of damage, is draining fast, or overheats during charging.

You may also be interested in this post: Car battery Vs. Bad Alternator | What you need to know?

5. The alternator replacement is of low quality

Have you replaced the alternator recently? Is the replacement overheating?

If so, then it’s worthwhile confirming that replacement alternator specifications are what is recommended by the manufacturer.

Compare the rated amps of the OEM (original manufacturer) alternator with those of the replacement.

Badly rebuilt Alternators

Again if it is a replacement that’s overheating and you’ve decided to rebuild instead of buying a new one, it might be that there’s an issue with the rebuild.

Contact a qualified auto mechanic. Take it up with the alternator supplier. They might provide a better-performing, reliable replacement.

6. The Alternator is undersized

If not, for example in case of a replacement that is undersized, for example using a 90 amp instead of a 120 amp rated alternator then the replacement will likely overheat in keeping up with the electrical power demands of the car.

7. The alternator is faulty

Do not rule out the possibility that the alternator is faulty. Perhaps it is the windings that are shorting or a loose connecting cable from the battery that’s connecting to the positive stud and sparking.

Any of these can lead to an overheating alternator.

You may also be interested in this post: 7 Common symptoms of short in the alternator

Is It Normal for an Alternator to Become Hot? How Hot Should It Get?

Yes, it is normal for an alternator to become hot while running. This is a combination of the engine bay being hot as the engine runs, which contributes to the heat buildup of the alternator.

Secondly, the flow of large currents through the alternator windings and the diodes for rectification also causes a buildup of heat in the alternator.

Fortunately, an alternator has an inbuilt fan that circulates air to cool. However, that does not rule out the possibility of the alternator overheating.

Temperatures in excess of what the alternator can handle lead to premature alternator failure.

Signs of an Overheating Car Alternator

In severe cases, there’ll be smoke from the alternator, it may become discolored or the nameplate may fold from the intense heat of the alternator.

Warning: Do not touch the alternator or any engine parts until the car has cooled down else you risk severe burns.

Tips to Fix an Overheating Alternator

If the car alternator is overheating, you can:

  • Inspect and remove any mud or other debris that may be blocking the alternator (once the engine/ alternator has cooled) so that there is enough air flowing to keep the alternator cool.
  • Check the battery cables for firmness or corrosion. Remove any corrosion, tighten, and make sure the battery terminals make clean firm contact with the battery posts.
  • If the battery shows signs of failure such as overheating during charging, or draining fast, arrange to have it rested at a reputable auto parts store. Replace immediately if the battery is confirmed as damaged.
  • if the battery cables are clean and firm, and the battery is confirmed to be in good condition, it might be that the alternator is faulty. Arrange to have the alternator tested at a reputable auto parts store. Replace with a type recommended by the manufacturer.

Related Questions

1. Why an Alternator Overheats yet the Car Engine is Off?

If the car alternator is hot when you touch it even when the engine is off (and should have cooled), then there might be an issue with the alternator such as a short-circuit in the windings, or diodes, which may drain the battery charge.

Contact a qualified auto mechanic.c. You can have the alternator tested at an auto parts store.

2. Can a Bad Battery Lead to Overheating of an Alternator?

It’s true – A faulty battery can lead to overheating of an alternator. How you may ask?

For example, a battery with an internal shot may be the reason that the alternator is overheating.

Such a battery draws a higher current from the alternator, overworking it which then leads to overheating.

3. What Causes a New Alternator to Overheat?

If a newly installed alternator is overheating, confirm that it has the recommended capacity. It’s possible that it’s undersized and overworked leading to overheating.

Another possibility you should look into is the health of the battery and the firmness of wire connections.

Arrange for the car battery to be tested at a reputable auto parts store.

Make sure too that the battery cable terminals are clean and firmly connected to the battery posts.

Closing Thoughts

Overheating of an alternator is dangerous and can lead to permanent damage to the alternator.

The underlying causes should be immediately addressed else you risk having to invest in a replacement alternator.

Possible causes include loose or corroded wire connections, low air circulation around the alternator, a damaged battery, or even a faulty alternator.

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