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Old 05-01-2008, 03:01 PM   #1
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Default Another dying alternator?

I was replacing a brake line and caliper last night. I had the brake pedal blocked down to stop the fluid from draining out and didn't unhook the battery. After 3 or 4 hours of monkying around, the battery died. Got it jumped and took a quick 2 minute test drive and it was fine. This morning it had ZERO juice. The LED on my cig lighter voltmeter didn't even light up. Got it jumped again and made it to work. I can hear the alternator whining, so I know it'* going. The voltage hovers in the low 13'* when moving or reving, and drops to 12 when I brake or idle. When I shut the car off when I got to work, the voltage went to 11.9. 3.5 hours later, it'* sitting at 11.5.

The battery is a 6 year old Optima yellow top, charged by a 3 year old Napa Raylock rebuilt 140 amp alternator. I figure the alt is gone. Opinions on the battery? This will be the 3rd or 4th alt to die during the life of this battery so far.
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Old 05-01-2008, 11:08 PM   #2
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The voltage seems fine when I first start it, and then it gets progressivly lower as it warms up.
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Old 05-01-2008, 11:47 PM   #3
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I'd replace the battery too. Weak batteries are tough on alternators & it'* 6 years old anyway.
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Old 05-02-2008, 05:24 PM   #4
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Default batt

Sounds like you have a battery drain / short going on. Could be something stupid like the power antenna circuit or one of the alt rectifier diodes could of shorted to ground.
This will also cause it to whine and get hot.
Have you checked for a worn or slipping belt?

Any way to have the alternator tested? You should be running 13.8 - 14.2 volts at the battery with the car idling.
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Old 05-02-2008, 05:38 PM   #5
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It actually acted fine this morning and going to lunch. I had the belt off last week and it was fine. How would I check the rectifier diodes for a short?
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Old 05-04-2008, 05:28 PM   #6
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Easiest way without taking the alternator apart is to check your battery volts while its charging or unhook the alternator cables and see if there is a change in battery stanby voltage.
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