About a week ago I noticed the volt meter showing 12 volts. After parking the car for a few hours I started the car and it went back to roughly 14 volts. During last week I noticed 12 volts a few more times and now it seems to sit between 12.5 to 13v.

So I went by Auto Zone today to have them test it. They hooked up their tester and basically read voltage. Don't think it put any load on anything. With the car off, they read roughly 12.6 volts and said the battery was 100% charged. With the car running, I think when we first started it it read something like14.6 and then came down to 14.4 to 14.2.

So based on these readings it looks to me like the alternator is fine. Plus I haven't noticed any dimming or other issues. So now I'm wondering if there is something off with the gauge. Couple of questions:

1. Is this a common or uncommon issue?
2. If there is a bad part, what is it and where is it? Is it the gauge or is there a sending unit or what?

Thanks!
Mike

I think must people here treat it like the oil pressure gauge, as long it shows something it's working. My gauges are never constant either, the oil gauge is low until I rev it then it climbs. I don't often watch my volt meter but I bet it does the same thing just not much movement. If you want exact readings I have seen trucks with the after market gauges installed in the original gauge holes or just added else where. If I can't fix my tach someday I might just install an after market gauge.

You are seeing two different numbers. When the switch is on and engine off, you are reading pure battery voltage available to start the car, and it should be in the 12.5-13.5 range (if fully charged). When you crank the engine, you are reading battery voltage and alternator charging voltage, which should peak out at about 14.5 volts - you have to charge at a voltage higher than the battery is currently holding, or you can't cram any more 'lectrons in there. The alternator has a voltage regulator that makes the alt charge until the battery is crammed plumb full of 'lectrons, then reduces the charging rate to just the engine and accessory load.

In other words, yours is perfectly normal.

I figured the readings from a voltmeter are accurate. But I like the idea of the gauge. Given this, is there something to change that can improve the accuracy?

Quality aftermarket gauge, like Autometer, VDO. Probably money better spent on an aftermarket mechanical oil pressure gauge.

in my wife's 99 montero, voltmeter showed 10-11 volts at idle with headlights on.....had it tested without conclusive results. at the time, my wife wouldn't drive it until I replaced alternator and battery......got factory new alt and installed, got new battery and installed.........same reading on the stupid gauge now for years and no problems.............i think its just an inaccurate gauge, I wouldn't worry about it unless you have problems......I have no problems and an extra alternator now sitting in my garage