- On average, alternators last about 150,000 miles (240,000 km). That's around 7 years for the typical driver.
- If your headlights or interior lights dim or flicker while you're driving, that's a good sign that your alternator is going out.
- Jump-start your car, let it run for 5-10 minutes, then turn it off. If it won't start when you try to turn it on again, your problem is likely the alternator (not the battery).
- Avoid charging multiple electronic devices in your car at the same time to keep from overloading your alternator.
Alternator Lifespan
Alternators typically last about 7 years or 150,000 miles (240,000 km). Your alternator's lifespan depends on the quality of the part, how hard it has to work, and other factors. But generally speaking, you can expect it to last for several years at least. Expect to pay between $500 and $1,000 to replace your alternator with a new one (this includes installation). A remanufactured one will cost less but won't last as long. When considering your budget, think about how long you plan to keep your car. If you're going to sell it within the next year, you might not want to invest in a top-of-the-line replacement.
How Alternators Work
Alternators convert mechanical energy to electrical energy. Think of your alternator as a tiny generator. While you're driving, it uses the mechanical energy from your car to create the electrical power needed to keep your battery charged and power all of your car's electrical components, such as your headlights, stereo, and windshield wipers. When your car isn't moving, your alternator can't create any energy, so anything electrical you have going is drawing directly off the battery—keep this in mind if you're idling in a parking lot charging your phone.
Signs of a Failing Alternator
Your battery warning light comes on. This warning light might look like a battery, but it actually indicates a problem with your electrical system generally. If your battery light comes on while you're driving and never goes off, that's a pretty good sign that you should get your alternator looked at. Sometimes your battery light will flicker on and off while you're driving. That's also a sign that you have an alternator issue. Generally, it indicates that your car's electrical system is getting its power straight from the battery, not from the alternator.
Jump-starting your car doesn't work. If your car starts when you have the cables connected, but as soon as you turn your car off to disconnect the cables, it won't turn on again, your battery is likely dead because your alternator failed to recharge it. Pay attention to the clicks your car makes when you try to start it. If it's a fast, repetitive click, that means it's the battery or alternator. Just a single click? That means you probably need to replace your starter.
Your headlights or interior lights flicker or dim. If you turn on your headlights and they just don't seem as bright as they used to be, or they dim while you're driving, that's a sign that the alternator isn't sending them enough power. Your interior lights might do the same thing, or they might flicker and pulsate instead of staying on steadily. Often, this is particularly noticeable if you're running a lot of electronics—and it also gives you a temporary fix. For example, if your headlights dim while you're charging your phone, unplug your phone and see if they brighten back up. A lot of people first notice this for the first time when it's raining because a lot of electrical components are working at once—the headlights, the windshield wipers, and typically the car stereo, as well as the GPS or any other devices.
There's a whirring or whining sound coming from under the hood. It can be hard to hear sounds coming from under the hood while you're driving, but if you do hear this, it could mean your alternator's about to go. You might also hear this sound right after you start your car. This sound could also mean that the alternator belt is loose. As long as that's the only issue, it's cheaper and easier to replace the belt than to replace the alternator itself. If you're replacing the alternator belt, make sure to take photos of the belt set up prior to making any changes so that you know exactly how the belt should be routed around the various pulleys. Make sure the replacement belt is the correct length by comparing the old belt to the new belt.
Your stereo or other accessories turn off while you're driving. You're rocking out to your favorite song when suddenly your stereo just goes silent. Or you can't get your phone to keep charging. If this is happening while you're driving when it was working just fine before, you probably need to get your alternator looked at. Keep in mind this could also be a faulty cable or connection. But if those seem fine, your alternator might not be providing enough power.
There's a burning smell coming from under the hood. This is a metallic smell similar to the smell that comes from fried electronics. A burning smell is never good—especially if you're driving. Pull over and turn off your car as soon as it's safe to do so, then have your car towed to an auto shop. If the burning smell is coming from your alternator, it's a sign that it was overloaded and burnt out. This might happen if you're running a lot of different electronic devices at the same time, especially when your car isn't moving.
Is your problem the alternator or the battery?
If your car won't start, it could be either. Your alternator needs the mechanical energy from your engine to run, so your car uses your battery to start. A car that won't start definitely means your battery's dead—but it could also mean that your alternator is dead and your battery's fine. To test this, go ahead and jump start your car and let it run for 5-10 minutes. Then turn it off and try to start it up again. If it won't start, that's a sign your alternator is the real problem. If you're more mechanically inclined, you could also check your alternator's output yourself using a voltmeter.
If you have electrical issues while driving, it's probably the alternator. While you're driving your car, the alternator supplies all of your car's electrical needs. Any kind of problems with lights flickering or dimming, stereo turning on and off, or windshield wipers not working you can blame on the alternator. Check all the wiring and connections before you assume it's the alternator (or get a mechanic to do it for you). You wouldn't want to spend hundreds on an alternator when the problem is really a loose cable.
If your electrical problems come and go, it's probably the alternator. When your battery's dead, nothing will work at all. But as your alternator starts to go, you'll find that the electrical components in your car work intermittently. This is usually because your alternator's working enough to charge your battery a little, then your electrical systems pull the power they need from the battery. Check your wiring and connections, especially if you've recently installed after-market accessories. You could have a loose cable causing the issue.
Maintaining Your Alternator
Charge a drained battery fully rather than making your alternator do it. Recharging your battery is part of your alternator's job. But if it's fully drained? That's a huge load to put on your poor alternator. If your battery's dead because you were blasting your car stereo while parked or accidentally left your headlights on, recharge your battery instead of just jump-starting your car and taking off.
Get warning signs of a bad battery checked right away. If you have to jump-start your car, go ahead and make an appointment with a mechanic to get your car checked out. The longer you put it off, the more strain you're potentially putting on your alternator. Same goes for any other warning signs of an electrical problem. If your lights are dimming, your radio cuts in and out, or your battery light comes on, get it checked out right away.
Watch for fluids leaking into the alternator. Any time you have a leak in your car, take it to a trusted mechanic and get it fixed as soon as possible. But if the fluids happened to drip down onto or into the alternator, that's bad news and could cause a short. If you think fluids leaked into your alternator, be sure to let your mechanic know. Say something like, "I think that leak also dripped down into the alternator. Can you check that for me as well?"
Avoid idling for an extended period of time. When you're idling, the alternator isn't getting any mechanical energy from your engine to convert into electrical energy. Sit for too long and you risk draining your battery. This puts a lot of strain on your alternator since it has to charge it back up. When you're waiting somewhere, turn your car off if you can (and roll the windows down). If the weather won't allow that, at least turn off as many electronics as possible, such as the lights and the stereo.
Charge electronic devices individually for short periods. When you charge several different electronic devices at the same time, you're putting a huge load on your alternator that will cause it to fail faster. On long road trips, take turns—and remember to pull your cable out when your device is charged. Using a lot of different electronics in your car at the same time has the same effect. If you want to get the maximum life out of your alternator, stick to the devices your car came with rather than overloading it with after-market options.
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