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Is my alternator failing?

Tiny
THESMTRITT
  • MEMBER
  • 2000 MERCURY MYSTIQUE
  • 140,000 MILES
I have a 2000 mercury mystique that won't start unless I jump it off another vehicles charge. I have tested the battery and it's 100% so my next thought is the alternator. I can't drive it to a car parts store because it dies if I drive it after about 30 feet. Since an alternator is about $150 for the low end refurbished ones, I want to exhaust all other options before I pull it off just to test it. I don't have a voltmeter, but I do hear a whining from the front end when I turn on my headlights, radio etc. After jumping it off. Does this sound like it could be anything but an alternator issue?
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Sunday, September 2nd, 2012 AT 5:29 PM

2 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,873 POSTS
You can't expect to test anything or find the problem without test equipment. First of all, get an inexpensive digital voltmeter. Harbor Freight Tools has one for less than ten bucks that works perfectly fine.

Measure the battery voltage first with the engine off and holler back with that number.

With the engine running the battery voltage must be 13.75 to 14.75 volts. If it is low it won't be charging the battery. How are you determining the battery is fully charged? If it is you shouldn't need to jump-start it to start the engine.
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Sunday, September 2nd, 2012 AT 5:46 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
With a 100 % battery, the only thing that can cause non cranking would be bad battery terminals or ground circuit connections.

Give them a check. Try using a jumper cable across the battery negative terminals and engine to see if it works.
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Sunday, September 2nd, 2012 AT 5:51 PM

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