Do I need to replace my car's alternator?

Is it undercharging your batteries?

Is it overcharging?

Does the battery warning light suddenly light up?

Is there suddenly a smell like burning rubber in your engine bay?

Do you hear high-pitched whirring noises when you step on the gas?

You can tell if your alternator is undercharging when your headlights suddenly dim or flicker while you are idling the engine, or even when you are driving down the road. When the alternator is undercharging, it might cause the battery to discharge. If this is the case, you will need to change your alternator sometime soon.

You can tell if your alternator is overcharging your car battery if you are replacing your car's lights (headlights, turn signals, etc.) every month or so. The excess amounts of electricity coming from the alternator is causing the delicate filaments in the bulbs to burn out faster than they are supposed to last between 500 to 1,000 hours. If you are replacing them before they barely break the 50 hour mark means that it is getting too much juice. This is a sign that your alternator is getting ready to bail out on you.

In some cars the light might not be shaped like a car battery, it might just be three letters, like ALT for alternator, or GEN for generator. Whatever the case may be, if there is a warning light that suddenly pops up, odds are that it is a problem with the alternator.

The alternator works because its crank shaft is spun by a belt connected to the engine of the car. If the crank shaft gets stuck, or if it gets hard to spin because of failing bearings in the pulley, the rubber belt that spins it will rub against the pulley, causing it to heat up and melt. If the crank shaft will not turn, the alternator will not produce electricity.

That whirring noise you are hearing comes from the broken bearings inside the alternator. In some cases, the alternator will still function as normal, but you will need to deal with the annoying noise. However, there are times when the broken bearings seize up the alternator, which means you need to replace the whole thing. On the other hand, if the damage is not that serious, you can just have the bearings replaced and then it would be fine.