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Q: Can 2 serpentine belts need replacing within 11 years and can the alternator suddenly fail without warning ?

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The original serpentine belt was replaced in 2008 as part of my 75K mile tune up. Yesterday, my battery warning light came on and a message appeared in my DIC that said battery not charging. I replaced the battery and the warning messages went off. While driving it today they came back on. I took it back to the dealership. My battery now has 65% life left in it. They started the diagnoses of my engine. Apparently, my serpentine belt is "bad" and my alternator is failing. However, it drives perfectly fine. There is no dimming of lights, no engine stalling or odd noises. Is it possible for an alternator to fail without any warning? (It is the original one that came with my suv.) Is it normal to replace two serpentine belts in 11 years with less than 130k miles on my suv? Could it be anything else that they are overlooking? I would really appreciate any suggestions you could recommend. Thanks!

My car has 129683 miles.
My car has an automatic transmission.

A: Hello. There is a huge variance in manufact...

Hello. There is a huge variance in manufacturer estimates of serpentine belt lifetime. This is understandable because operating conditions vary, vehicle designs vary and the belt material will degrade at different rates. You should get at least 50,000 miles out of the belt. If less than 50,000 miles there is a problem which itself could vary in cause (lousy belt quality, vehicle design issue, defective pulley bearings and so forth). In your circumstance, you want to make sure that all of the ball bearing mounted pulleys that the belt rides on are in good condition.

These bearings sometimes wear out and the grease can dry out, creating friction and unwanted noise. Also, the belt tensioner should be inspected. Basically, any and everything that the belt runs on should be inspected for smooth operation. Alternators are diagnosed by measuring their voltage output, both loaded and unloaded. As long as the alternator’s output (voltage) is within specification, and it holds up under load (with all car accessories on) it is usable. The thing to do is ask exactly what the output of the alternator was during their diagnostic. Some shops should even be able to print out these test results (the voltage output) or at least demonstrate the results for you by showing you the test instrument in action. Should you desire a second opinion to be sure you are getting good advice, YourMechanic, in your local area, will be pleased to help you.

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