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Is my alternator bad?

Old 04-16-2018, 09:50 AM
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TheGreek!
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Default Is my alternator bad?

I just got my first C4 (an 85) a few weeks ago, I'm still on the learning curve with it. My volt meter is reading 17 volts and there's a red light to the left of it that's on. I think thats too much voltage, that it should be around 13-14 volts. Is the red light next to the voltage reading a warning light? The voltage holds pretty steady though, if the regulator in the alternator was bad wouldn't the voltage be all over the place, wouldn't it keep going up and up as engine speed increases? I'm curious what the volt meters in other people's C4's read so that I can be sure that the alternator is bad (I think it is) before I go and blow the cash for a new one. Any help is appreciated.

Edit:

I just put my volt meter on it and its reading 14.5 volts at both the alternator and the battery but the voltmeter on the dashboard is still reading 17 volts with the red light on next to it. I checked it with a second voltmeter just to be sure that I wasn't getting an erronious reading from the first voltmeter and it's reading the same, 14.5 volts. What could be causing the discrepancy in the readings, why is the voltmeter on the dashboard reading 17 volts when the actual voltage is only 14.5?

Last edited by TheGreek!; 04-16-2018 at 10:49 AM.
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Old 04-16-2018, 09:54 AM
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Originally Posted by TheGreek! View Post
I just got my first C4 (an 85) a few weeks ago, I'm still on the learning curve with it. My volt meter is reading 17 volts and there's a red light to the left of it that's on. I think thats too much voltage, that it should be around 13-14 volts. Is the red light next to the voltage reading a warning light? The voltage holds pretty steady though, if the regulator in the alternator was bad wouldn't the voltage be all over the place, wouldn't it keep going up and up as engine speed increases? I'm curious what the volt meters in other people's C4's read so that I can be sure that the alternator is bad (I think it is) before I go and blow the cash for a new one. Any help is appreciated.
Probably bad. Drive over to Advance and they will test it

Last edited by Cruisinfanatic; 04-16-2018 at 09:55 AM.
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Old 04-16-2018, 10:03 AM
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Originally Posted by Cruisinfanatic View Post
Probably bad. Drive over to Advance and they will test it
I was thinking on bringing it in to be tested (we dont have advance auto out here in Tucson, all we have is O'Reilly's, auto zone, and pep boys and the alternator has to be removed so that they can put it into their test machines). I think it's more than likely bad but I wanted to hear from the people on here first about the red light next to the voltage reading and what the voltages in their cars are.
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Old 04-16-2018, 10:16 AM
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Originally Posted by TheGreek! View Post
I was thinking on bringing it in to be tested (we dont have advance auto out here in Tucson, all we have is O'Reilly's, auto zone, and pep boys and the alternator has to be removed so that they can put it into their test machines). I think it's more than likely bad but I wanted to hear from the people on here first about the red light next to the voltage reading and what the voltages in their cars are.
17 volts is too high. It's overcharging, and will cook the battery. The regulator (inside of the alternator) has failed.

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Old 04-16-2018, 10:19 AM
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Do you have an actual voltmeter ?
If yes then go measure batt voltage across the battery terminals with the engine running at idle. Should be right around 14 volts.
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Old 04-16-2018, 10:41 AM
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Ok the mystery just deepened. I just put my voltmeter on it and it's reading 14.5 volts at the alternator and 14.5 volts at the battery too but the voltmeter on the dash is reading 17 volts. What could be causing the discrepancy?
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Old 04-16-2018, 10:59 AM
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I'm going to start a new thread with my findings with the voltmeter but I can't figure out how to delete this thread now that I'm sure that the alternator is good.
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Old 04-16-2018, 11:46 AM
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Originally Posted by TheGreek! View Post
I was thinking on bringing it in to be tested (we dont have advance auto out here in Tucson, all we have is O'Reilly's, auto zone, and pep boys and the alternator has to be removed so that they can put it into their test machines). I think it's more than likely bad but I wanted to hear from the people on here first about the red light next to the voltage reading and what the voltages in their cars are.
Auto Zone does testing on the car
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Old 04-16-2018, 11:51 AM
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Originally Posted by TheGreek! View Post
I'm going to start a new thread with my findings with the voltmeter but I can't figure out how to delete this thread now that I'm sure that the alternator is good.
Just use this thread.
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Old 04-16-2018, 01:54 PM
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Don't drive, it is right on top, bring it in and test it,if bad get e new one.
Then check wiring ect. Good Luck

Last edited by xrav22; 04-16-2018 at 02:54 PM.
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Old 04-16-2018, 02:40 PM
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Originally Posted by TheGreek! View Post
Ok the mystery just deepened. I just put my voltmeter on it and it's reading 14.5 volts at the alternator and 14.5 volts at the battery too but the voltmeter on the dash is reading 17 volts. What could be causing the discrepancy?
So your Voltmeter says 14.5 and the dash says 17? I'd go with the Voltmeter and forget the dash. My tach hasn't been accurate on it till I got all my gauges calibrated.

If you feel that bad about it, go take it to a rebuild shop and have them check it. I had alternators and starters tested by them that passed but when opened up, you see issues.
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Old 04-16-2018, 02:44 PM
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Originally Posted by aklim View Post
So your Voltmeter says 14.5 and the dash says 17? I'd go with the Voltmeter and forget the dash. My tach hasn't been accurate on it till I got all my gauges calibrated.

If you feel that bad about it, go take it to a rebuild shop and have them check it. I had alternators and starters tested by them that passed but when opened up, you see issues.
How did you get your gauges on the dash calibrated? Is it even possible to do that? What year is your car?
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Old 04-16-2018, 02:54 PM
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Originally Posted by TheGreek! View Post
How did you get your gauges on the dash calibrated? Is it even possible to do that? What year is your car?
https://www.corvetteforum.com/forums...t-cluster.html

Mine is a 91
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