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Had the factory alternator totally short out while driving?

Tiny
FVEE8
  • MEMBER
  • 2008 BUICK ENCLAVE
  • V6
  • 2WD
  • AUTOMATIC
  • 186,000 MILES
I got maybe 3 minutes of driving before it went dead stick and coasted to a stop, battery to zero volts. My battery was only 1 year old at most. Installed a new (not rebuilt) alternator and charged up the battery, started the car and all was good for a week. Now after driving maybe 15 minutes or longer, I most times get a big drop in the charge voltage, like from normal 14.3V down to somewhere around 12V, twice I got the red battery light flash on. Stop and restart the car most times cures things for short while. It has been a very hot summer, and the battery held a charge just fine for 2 weeks without starting it up. Bad alternator or battery or?
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Thursday, September 12th, 2024 AT 7:08 PM

7 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,536 POSTS
Yep, I would replace the battery, it sounds like it is defective. Also, I would check the positive battery cable for corrosion which can be internal and hard to find. These instructions may help you. Check out the images (below). Please let us know what happens.
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Friday, September 13th, 2024 AT 9:16 AM
Tiny
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Thank you for your reply. I just happened to have a new battery (for another car) sitting in the garage that I will give a try, and also testing for any voltage drops. More to come.
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Friday, September 13th, 2024 AT 6:31 PM
Tiny
KEN L
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Sounds good! Have a nice weekend.
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Saturday, September 14th, 2024 AT 6:49 PM
Tiny
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I tested today with my new battery in parallel using jumper cables.
For the 1st 10 miles or so it was 14.3V with the AC on high.
Then the voltage dropped to about 13V, further driving it was between 13 and 13.4V or so, depending on the RPM.
Also note that it seems since I installed the new alternator that my engine has a new low frequency rumble/vibration like it is struggling or something? It does this no matter the voltage output.
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Thursday, September 19th, 2024 AT 9:03 PM
Tiny
KEN L
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The alternator seems like it is working okay, the voltage will naturally go down as the battery is charged up. When the engine is running how does the serpentine belt tensioner look, is it bouncing around? I have seen these tensioners cause vibrations. Here is what I am talking about. Check out the images (below). Let us know how it goes.
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Friday, September 20th, 2024 AT 10:22 AM
Tiny
FVEE8
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Thanks for your replies!
I had just replaced the tensioner, and idler(s) pulleys before the Alternator shorted, and it did freeze up and burnt the belt off so maybe it do some additional damage. I will take a look while its running.
The vibration feel/noise is strongest between 1400 and 2000 rpm, goes away if I lift off the throttle.
I removed the parallel battery and drove 35 miles with 1 stop, voltage stayed above 14 the whole time, pretty steady.
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Friday, September 20th, 2024 AT 12:20 PM
Tiny
KEN L
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That part sounds like it is fixed, I would check the pulleys for burnt rubber on them.
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Friday, September 20th, 2024 AT 1:53 PM

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