How Much Does it Cost to Replace a Semi-Truck Alternator?

The alternator in your truck has a crucial function to perform: it feeds your semi-truck a continuous stream of high-amperage power to keep everything powered up and running smoothly. The alternator is one of the components that only gets a rest when the truck is off; when it’s on, it is subject to some of the most grueling and demanding conditions.

Since the alternator is the key component in your truck for transforming mechanical energy into electrical energy, if it goes out, your rig has no power to actually run. Sure, your battery may get your truck started, but without an alternator, your lights, air, heat, radio, power outlets, GPS and more are useless, and you have no way to recharge the battery. This means it is a top priority to replace your alternator when it dies because you can’t run miles without one.

We’re going to take a look at what it may cost you to replace your alternator, as well as how long that repair may take your truck off of the road We’ll also examine some of the common indications that your alternator is going to go bad, and you might be able to test your alternator to determine for sure if that’s your issue.


Cost to Replace Alternator in a Heavy-Duty Truck

The two main factors in determining the cost to replace the alternator in your truck are the parts cost and the labor cost for the replacement job. For a semi, an alternator is going to cost anywhere between $150 and $600, depending on the needs of your electrical system. Since the replacement job itself should only take a few hours, some trucks can be ready to go for only around $500 total, while others will be closer to the $1,000 mark once taxes and ancillary fees are included.

For those that are mechanically inclined, replacing an alternator is a relatively simple job. Parts can be obtained easily, and there are countless how-to videos on the internet. The biggest problem with this is that you need to be absolutely sure the alternator is the problem, or you’re just wasting money and time. This is why using a trusted local shop is usually an easier way to make sure it’s fixed right the first time.


How Long Does it Take to Replace an Alternator?

Replacement of an alternator is not a complex job, and generally can be done in just a few hours. Those familiar with the process can often get it done in under two hours. The process itself is relatively simple, and the part is often only held in by 2-3 bolts.

Once the old alternator has been removed, the new one is able to go right in its place, with no modifications. Once mounted and secured, the drive belt will need to be replaced. It is crucial that the alternator is installed in the correct orientation and that the belt is routed in the correct direction when finishing up. Alternators can only work properly when turned in the right direction.


How Long Should a Semi-Truck Alternator Last?

This is a pretty wide-open question and there are a lot of variables that can affect the answer. Some of the things that affect how long an alternator will last include the mileage that it is used over, the electrical load that it usually supports, and even the climate that the truck operates in most of the time.

The demands of semi-truck alternators are built into the component itself, so even though truckers use their vehicles far more than most, the alternator should last a proportionately longer time. You can expect a recently replaced alternator to go for another 70,000 to 100,000 miles.

That lifespan can be considerably reduced by putting high loads on the alternator consistently and operating in extreme conditions. Drivers that consistently push their electrical systems to the max may see a significantly shorter lifespan than the average. Running high-amperage appliances or accessories in the cab for long periods, particularly at idle, can cause the alternator to generate damaging heat.

Drivers that operate in dry, dusty, or salty environments will also see a decreased lifespan on their alternators, generally speaking. Heat is damaging to any electrical components, and dust not only insulates them but reduces conductivity in crucial areas.

Drivers along oceanic coastlines will likely need to replace their alternators more often due to the corrosive effects of the salt and moisture in the air. Corrosion causes damage to the bearings and the pulley, resulting in the alternator seizing up and potentially burning up a belt.


Signs Your Alternator is Going Bad

Since alternators are electrical components, sometimes troubleshooting can be difficult. The symptoms may not be the same from one failure to another, and signs may vary. However, here are the most common ways that you can tell that your alternator may be going bad.

Odd Noises

A common way that alternators fail is by their bearings going bad, which causes them to resist smooth operation and build up excess heat. This bearing degradation will almost always result in some noise from the alternator or its pulley. One common noise is a constant squeal created when the alternator is seized or nearly seized, which creates drag on the belt, resulting in a loud belt squeal.

Stalling Or Difficult Starting Up

The battery will start your truck, but the battery is charged by the alternator. This means a failing alternator will not charge your battery sufficiently, and the next time you try to start your truck you may notice that it is slow to start or that the battery isn’t able to provide a start at all.

Dimmed Headlights

Dimming headlights is a standard signal that the alternator in your truck is going bad, as this means that it can’t keep up with heavier electrical load demands. At night, when you put your headlights on, the additional current demand will cause your headlights to illuminate at a diminished level. This may also be caused by old bulbs or cloudy lenses, so potential causes like those should be eliminated first.

Dashboard Light Warnings

One of the easy ways to determine if your alternator is not performing up to par is if you see specific, or maybe not-so-specific, warning lights popping up on your dashboard. Common lights that may indicate problems with the charging system include ALT, GEN, the battery light and even the “check engine” light. These indicate your truck isn’t getting the expected voltage from your alternator.

Miscellaneous Electrical Malfunctions

The alternator is the heart of your truck’s electrical and charging system, so any malfunctions in the alternator may manifest with other electrical malfunctions. These malfunctions include slow power windows, seats and mirrors, as well as weak radio reception or significant interference, problems with the air conditioner, or sudden issues with any other electrical component.


How to Test Your Alternator

Testing electrical components can be tricky sometimes, but if you have the right equipment you can test your own alternator to determine if that’s the part you need before you commit to buying anything. You will need a multimeter to test your alternator.

First, rule out that your battery is to blame by testing the voltage across the terminals while the truck is off. It should read somewhere between 12v and 13v. Then, check the same reading with the truck running, and you should see a reading of 13v to the low 14v range.

Now, while the truck is running and you’re measuring the voltage, turn on a significant electrical load. If the voltage drops significantly, then you may have an alternator issue. No matter what you turn on, you should not measure less than 13v with the truck running.

The only other way to be sure is to either bring the alternator into a shop for testing or take the whole truck in to have the entire generator and charging system checked.


perform regular tire maintenance on your truck tires

Protect Your Semi-Truck with Blaine Brother’s Preventative Maintenance Guideline

The best way to help prevent any surprise component failures or unexpected repairs is to make sure you’re partnered with a trusted local repair shop like Blaine Brothers. We offer a complete, comprehensive preventative maintenance program for heavy-duty trucks. We’ll make sure every system and component on our extensive checklist is inspected and tested so that you can stay current on your truck’s health and maintenance needs.

Here are some preventative maintenance tips that anyone can do that will help keep your alternator in good shape:

  • Make sure the alternator is clean and free of built-up dirt, dust, or mud.
  • Keep all connections clean and free of dirt, grease, or other insulative substances that can rob the system of conductivity.
  • Ensure that your belt is properly tensioned to spec. If the belt is too loose, the alternator won’t work and if it’s too tight it can cause premature bearing wear on the alternator and other components.


For Alternator Replacement Experts, Contact Blaine Brothers

If you need alternator service, or your alternator is showing one or more indications that it may be ready to fail, you should make sure you have a trusted truck shop that is ready to get you fixed and back on the road. Reach out to Blaine Brothers today with any questions you may have or to schedule service!

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