Causes of Premature Alternator Failure

Question

I bought my car brand-new a few years ago, with only 50 miles on it when it came off the lot. It's perfectly stock - no modifications made, though some parts have been replaced for repair purposes.

Because I have a long commute, I blew past the mileage cap for the manufacturer's bumper-to-bumper warranty long before I hit the time limit. Even so, I'm now just a bit outside of what would have been the time limit on that warranty coverage anyway.

Now, with just over 74,000 miles on the car, I'm being told my alternator is making noise and may fail soon. It hasn't been giving me problems in terms of power delivery yet, but the diagnosis does explain some other minor symptoms I've noticed. This was discovered while I had it in the shop for some unrelated issues.

The real kicker though, is that this is already my second alternator. The first failed somewhere around 40,000 miles (outside of warranty due to mileage alone, at the time). That time, it did reach the point of having substantially reduced performance before I realized there was a problem and replaced it.

So now, on a car bought brand-new, I've had two alternators either fail or show indications of imminent failure within around 40,000 miles or less.

All of the vehicles I've owned before this one were bought with at least 90,000 miles on the odometer. For each of those cars, I put at least 100,000 of my own miles on them and only (if ever) had to replace their alternators once.

The first alternator on my current car obviously came straight from the manufacturer. (Again, car was bought brand-new.) The second may have been re-manfactured (I don't recall off the top of my head - will be contacting the shop that did the work when they're open again). Regardless, it seems unusual to me that both should fail so early and both around the same time.

What could be causing this?

Vehicle details:

2012 Dodge Avenger SXT
2.4 L GEMA I4 DOHC 16V Dual VVT 6-speed automatic, FWD

Answer 1

Noise from an alternator can be early symptoms of it going bad. It's generally the bearing inside the alternator. You have a couple. With most modern vehicles the alternator bearings are located on the outside shaft and one for the rotor inside the alternator. When the shaft bearing starts to breakdown you'll notice a squealing noise or screeching when the car is running. This usually won't cause the alternator to malfunction UNTIL the bearing destroys itself. When I've seen intermittent performance on alternators, its usually the bearing(s) that lie between the rotor and stator.

That aside, you really shouldn't be going through that many that quickly. If an alternator is not installed correctly it can cause the bearings to go bad. This is because the serpentine belt that drives it could possibly be putting EXTRA stress on the pulley in directions is shouldn't be, thus causing the shaft bearing to prematurely expire.

The quality of the parts you install are also a HUGE factor when talking about an issue like this. You should look up reviews and quality assurance on the alternators you're buying. They could just be generally poorly manufactured.

Oil, fuel and debris are another thing to consider. If there is a spot that is leaking or spraying small amounts of oil or sediment into the rotor and stator, this can DEFINITELY cause premature failure. It's not always visually obvious, so keep that in mind.

If you want you can take this to an automotive electrical shop and they can rebuild it. You can usually gather a wealth of knowledge from them if you just ask the right questions and make friendly conversation.

ALWAYS keep in mind that a 2nd opinion is important as well. I practice heavily in "Last Case Diagnostics". When a shop or person is having an issue that a shop can't figure out, or if the individual is concerned that their shop isn't doing something right; I find scientific reasoning and repair the issue. You might be able to find a shop near you that can do this for you. It's a dying breed of technician, but you might be able to find someone near you.

Answer 2

Old alternators on old 1960s cars were great. They were much better than the generators that they replaced. Generators needed current limiting which was generally done with electromechanical regulators made by companies like say Lucas UK or Delco USA. A generator would burn up charging a flat battery if it did not have current limiting or if the often temperamental regulator malfunctioned. This is because the generator has a very low output impedance meaning that there is not much intrinsic current limiting. Now the old alternator had a higher output impedance meaning that current limiting was not needed. In other words the old alternator was more idiot proof then the generator. Auto sparkie polytech courses stated that "You don't need current limiting with an alternator." I agreed with the tutors, but that was when I was thin and had thick hair. Many modern alternators especially Japanese get much more power out of a smaller size. They have reduced the output impedance to allow more current to flow when needed.So if you overload your car with accessories you can blow up your alternator these days. If you filled say a 1965 Studebaker with accessories you would just get a flat battery. Also you can blow a modern alternator when charging a flat battery or even when fitting a much larger battery to the car. These things just don't happen with 1960s cars.Some modern alternators have a thermal back off which throttles the current down as the copper gets too hot which gets around the problem without having to go back to the 1960s.

Answer 3

Years ago I had a VW Jetta Mk2 that would eat an alternator approximately every 18 months. Because this vehicle had an AC-compressor fitted lower down, the alternator sat on top with a short belt that drove it from the nearest pully. Common sense (and perhaps a little bit of Physics 101) told me that due to the way that belt pulls down on the alternator axle, this is likely the reason. My solution was to not tighten that belt too much. I figured that replacing the belt a bit more often costs less than replacing the alternator.

Answer 4

I can tell you straightforward, without a doubt that it was not the alternator but the decoupler pulley / one way bearing on the end of the alternator. I've done so many of these its ridiculous. They do take a beating though so there failure rate has alot to do with the driving style of the commuter. You see they way they work in a simple approach – when you rev the engine to 3k and let back off really quickly, usually the alternator will stay in tandem with the engine but in this design the one way bearing decouples and lets the alternator mass continue to spin until its revved and couples again or it slows from mechanical and electromagnetic counter force.

Answer 5

Mechanical factors can certainly eat alternators. In one of my older cars (a VW Mk2 diesel) I loved driving it with full AC fan almost all the time. The higher electric load contributed to earlier failure. Usually that failure was of the brushes, and for the 400 or so thousand miles I drove that car, I got real handy at soldering new brushes to the brush holder. As I recall, this needed to be done about every 80,000 miles.

My point is just that a high electric load could also be a factor in your frequent alternator replacements.