Battery/alternator what's your guess?
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Junior Member
Joined: Jun 2000
Posts: 18
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From: Royse City, TX, USA
Battery/alternator what's your guess?
1989 RS 350 New battery installed last tuesday. Other battery was a year over the date so I decided to change it out before the Texas summer hit. Daughter called other night and said car will not start, battery dead. Went and jumped off car this morning. Got car home and did some shade-tree checking. voltage on battery with engine running is 12.87 volts ( little low ) Unplug alt. and voltage is 11.87 When alternator is unplugged engine gains 300 RPM. The alternator is so hot you can't stand to touch it. Checked the temperature of case on alt. and it checked about 320 degrees. Engine is cooler to touch than alt. I thought maybe the alt. had gone bad but then why is it having to work so hard to charge. Amp guage shows about 10 amps output.
Supreme Member
Joined: Jun 2000
Posts: 1,295
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From: VA
Car: '91 Z28
Engine: L98 5.7L TPI
Transmission: 700R4
Axle/Gears: 323's
Sounds to me like the alt has gone... what's the voltage when it's running? If the alt's not charging the battery with the car running, that's how you killed the batt...
KAM
KAM
Supreme Member
Joined: Jul 1999
Posts: 5,183
Likes: 42
From: Oakdale, Ca
Car: 89 IrocZ
Engine: L98-ish
Transmission: 700R4
11.87 indicates a weak/dying cell in the battery.
I'd put a charge on it for a few hours before you head to bed, unplug the charger and in the AM check the voltage, should be 12.4-12.6volts, if not, the battery isn't holding the charge.
The Alt's run real hot anyways, but 320* seems awfully high, and the 12.87 volts out, seems too low as well.
FWIW my battery sits at 12.5 volts. With the engine runing I'm between 13.8 and 14.1, depending on what accessories are on.
I'd put a charge on it for a few hours before you head to bed, unplug the charger and in the AM check the voltage, should be 12.4-12.6volts, if not, the battery isn't holding the charge.
The Alt's run real hot anyways, but 320* seems awfully high, and the 12.87 volts out, seems too low as well.
FWIW my battery sits at 12.5 volts. With the engine runing I'm between 13.8 and 14.1, depending on what accessories are on.
Supreme Member
Joined: Jul 1999
Posts: 18,457
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From: Loveland, OH, US
Car: 4
Engine: 6
Transmission: 5
Sounds like a shorted cell in the battery, just yerbasic infantile failure. With a shorted cell the battery will look to the outside world like 5 cells at 2.2 volts each for 11 volts total instead of the usual 6 cells for 13.2 volts total, and the alt will work its little butt off trying to bring it up to the right voltage but of course won't be able to, and will overheat in the process. Take the battery back where you got it and have it tested. It might have torched the alt, but probably not if this didn't go on for too long. Have the alt checked too if you have any doubt.
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"So many Mustangs, so little time..."
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"So many Mustangs, so little time..."
ICON Motorsports
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