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Tom
January 9th, 2018, 06:12 PM
2012 JK with 65K miles.

It is my understanding that normal running vehicle voltage is 13.8 volts. I noticed the other day that my jeep is running at 14.8 volts. Then a day later noticed it was temperature dependent. 14.8 on cold morning. 14.3 in the afternoon. Today 14.8 in the morning, 13.8 when I started it after sitting in the sun. Upped to 14.3 as it cooled during my drive home.

I installed a radio the other day that warned of voltages over 15.8. Got me a bit concerned.

Question: Are my voltages and fluctuations normal? Is the an early sign of failure. Sounds like the regulator is part of the alternator and $600 replacement at a shop.
Terrafied
January 9th, 2018, 06:57 PM
14.2 volts is generally considered the "perfect" charging voltage and is about what you should see when testing charging voltage. A good alternator will usually produce between 14.0-14.6 charging volts. Sounds like your operating at about the correct voltage. There might be a slight effect caused by the cold that causes the fluctuations you are seeing in the morning after cold start as the system is trying to charge the battery and power your accessories when everything is cold. I wouldn't worry about it, sounds like it's well within the "good" range.
Bob
January 9th, 2018, 07:59 PM
Yes those are reasonable voltages. The voltage decreases as temperature increases (negative temperature coefficient) because that it how the lead-acid battery works. It requires higher voltages when colder to obtain the the same charging.
Patrolman
January 9th, 2018, 08:44 PM
The 15.8 is a bit concerning - rarely do I see anything that high from an alternator. Typically you should see between 14 and 15 from the alternator after a start. I would keep a close eye on it over the next few days to see if it continues to run higher than normal.
Tom
January 9th, 2018, 09:52 PM
The 15.8 is a bit concerning - rarely do I see anything that high from an alternator. Typically you should see between 14 and 15 from the alternator after a start. I would keep a close eye on it over the next few days to see if it continues to run higher than normal.
Have not seen it above 14.8

The radio just warned about voltage at or above 15.8 and I was thinking 13.8 engine running was normal.
Patrolman
January 9th, 2018, 10:32 PM
My misunderstanding - I thought it went up to 15.8. At 13.8 you are cool. That is "normal".