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What good is a voltmeter on dashboard?

Does the voltmeter on the car any indication of the condition of the alternator?
What does it measure exactly, or what good is it?

I have 2003 Ford Crown Victoria. This car has a voltmeter on the dashboard. There is no voltage mark, just a needle and high/low marks. The needle always sits just above the middle. I have never seen it move. I start the car, it pops to its usual position and sits there.

If it provided an accurate voltage measurement at the battery terminals, that could be useful info. For example the battery should measure about 12.5 volts first thing in the morning, before starting the car. And that measurement should go up to 14-15 volts once the engine is started, then taper off toward 13 volts as you run the engine for some length of time. You could also get an estimate on the battery health by turning on the headlights (with the engine off) and seeing how much the voltage dropped. The more it dropped, the worse the battery state. Or the same idea, but observe the battery voltage drop during cranking. So with an accurate voltage display you could potentially get a heads up the battery is about to fail, and start looking for a replacement battery. Or that the alternator is about to fail, so you’d better replace it otherwise you’d be stranded soon.


Car Talk Lackey
Great answer GeorgeSanJose!


With a gauge poorly marked (or not marked…) like this you have to assume the lower mark is 12 and the upper mark is 18.
That means a 6 volt difference. Split the difference and if the needle is around the middle of the battery emblem the system should be charging at around 14 or so volts.

I’m not a fan of gauges. I don’t find the info they provide to be very useful (other than the fuel gauge and speedometer). I prefer warning lights. Gauges rely too much on interpretation and driver judgment. If the engine temp is too high, turn on a light to warn me. If the oil pressure drops, turn on a light and chime to get my attention.

How high can the temp gauge go before it’s a problem? Sure it’s almost to the red, but it’s 100 degrees, I’ve got the A/C on and I’m pulling a loaded trailer over the pass at 75 mph. It’s hot, but is it too hot? I dunno. Just turn on a red light when it’s too hot so I know to do something.

Besides, gauges on modern day cars aren’t really gauges, more like indicators. I once compared the temp gauge on my 06 Lincoln to actual engine temperature. The gauge read right in the middle of the normal range at the time the engine was only at 140 degrees and stayed right there until the cooling fans came on at 220 degrees. What good is a gauge that reads the same over 80 degrees of temp? All they do is tell you “normal” or “not normal.” Might as well be a light.

I had a voltmeter on my jeep before. It’s quite accurate in reading the voltage of the battery and the alternator voltage with the engine running.

At what temperature should you be warned by a warning light?

I was able to diagnose and get replaced a bad head gasket before my engine overheated because I have a temperature gauge and noticed it was a tad higher than usual. Had it been a light instead of a gauge, it probably wouldn’t have illuminated until the temperature gauge got closer to the red. The head was barely (by a few thousandths of an inch) warped, but had I had a warning light instead of a gauge, it probably would have been considerably warped by the time I discovered anything wrong.


How many drivers ignore the gauges until the engine stalls or makes noises or smokes? I prefer accurate gauges myself but few cars have them. Ford’s oil pressure gauge is a total joke as it operates on an ON-OFF sender and moves the needle to the mid point at about 13psi where it remains until pressure drops. A light would be an improvement over that. But an accurate voltmeter can give a great deal of information for anyone who would pay attention to it.

I don’t normally click on any links ( I am able to do my searching for information ). This time I clicked on the link posted by Cyberbabe about Volt meters. The writing is poor and seems to be translated to English.

I’d say about 245*. As far as I’m concerned anything below that could be considered normal depending on engine load and ambient conditions. Most (I’d say over 90%) people are not as vigilant about monitoring gauges as you are. Or those that monitor the gauges don’t care.

A few years ago a friend had to relocate to AZ from WA. I helped him move the things the movers wouldn’t take. So we were driving my Chevy pickup loaded to the hilt, pulling a packed U-Haul trailer. We reached the Grapevine (a constant 6% grade up to the Tejon Pass out of the CA Central Valley). Trying to keep pace with 65mph traffic, halfway up the gauge was just about in the red. Turned off A/C and the heater on high. Still hot. Shifted out of OD, no better, then down to 2nd to try to pump that coolant through and spin the fan faster, still hot. Soon the gauge was pegged red AND the warning light was on. She’s really cooking now! I can smell how hot she’s running. But we’re almost there, just another minute or two and we’ll crest the pass. Kept the heat cranked and out of overdrive on the way down and she cooled right off.

Moral of the story…gauge or light, it’s rare to find people who really pay attention to them.

I like temp gauges and voltage gauges. Remember one car died, then the voltage "idiot light came on. Temp too low or rising not to alert level I like that. Bought a new battery, voltage gauge 14 while running, sounded a little slow cranking, about 10 volts charge indicated with engine off. Took it to be tested, 800 cca battery maybe 6 or 7 years old, 460 cranking amps. New battery as sub zero temps this week, and I like the car to start when I need it.

I LOVE GAUGES! (though I spell it wrong every time guage, guess because it is pronounced differently then gauze or maybe because we are involved in relief work in Guatemala, no guarantee)

So you’re saying that because some companies do gauges poorly, some people ignore gauges, and some engines’ cooling systems can’t keep up under strain are reasons to abandon gauges that work well in cars that have cooling systems that work well?

That’s some weird logic. I’m glad you didn’t design the dashboard or the cooling system on my car.

There is a reason many of us call them “idiot lights” (not that I would ever call you an idiot).

What makes you think someone who ignores gauges would notice a light? Why not have both?

Gauges that accurately represent conditions under the hood are a thing of the long gone past. Show me a modern day car that has clear demarcations denoting engine temperature, oil pressure, etc that can be proven to be directly related to engine conditions. My 06 Lincoln temp gauge reads in exactly the same place in the “normal” scale from 140 to 220 degrees. How can that be of any use?

Gauges are no longer directly connected to a sending unit on the engine, the info is relayed through the engine computer to the body controller or instrument cluster module which then places the gauge at some pre-programmed location. So that you can look at your car and say “Gee, my luxury sedan doesn’t run any hotter when I’m banging up the mountainside at 80mph. What a great car!”

I wish that this weren’t the case, but more than once I’ve had someone come to the counter and say “I need help with my car, my ‘check gauges’ light is on.” “OK, which gauge isn’t reading normally?” “I don’t know.”

Mine didn’t need “demarcations denoting engine temperature” in order to be useful.

It isn’t that I don’t understand your argument. I understand your argument, and yet I don’t find it logical or compelling. You make a good argument to have both gauges and idiot lights, but you haven’t made a compelling argument for abandoning gauges that work well on cars whose systems work well that are driven by people who pay attention to what their gauges are telling them.


Real gauges have no sending units.

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Not sure where everyone is going here, but yes it turns out my oil pressure guage is a fallacy, but think temp, alternator, tachometer speedometer are actual representations.

lol … me too, that word is pretty much impossible for me to guess the spelling the first time. Althoug if you think about it gauges is spelling like it sounds, gay-gez, so maybe now I’ll remember it goes g-a not g-u

I don’t accept the premise of the idea. Your Civic, if I recall, is quite old in automotive years. I maintain that in current, modern-day cars, there are no temp gauges that accurately and reliably warn the driver of minor variations in operating temperatures or pressures so as to make them significantly useful. Gauges have become more decorative than useful when it comes to informing the driver of minor variations in engine conditions.

I also think you’re giving the general motoring public more credit than they deserve when it comes to monitoring gauges. Sure, you picked out a failing head gasket by noticing a slight increase in engine temp. Honestly, how many other people would?

Last month a customer was grumbling about the cost to have a no-start condition on her car diagnosed. She felt the $100 diag fee was excessive when, after the diagnosis, we repaired the car for $10. I handed off the customer to my service writer. What I really wanted to say was that “If your fuel gauge reads low, then your low fuel light comes on, then the car quits, then you call a tow truck, you deserve to pay a lot more than $100 to get your car running again.”

Drives me crazy, wifey I can still go 33 miles till empty per readout, It is on E put gas in it! 1/4 tank min 1/2 tank usual till I get gas.

in case you don’t know, you can buy $12 voltmeters on Amazon that plug into the cig lighter outlet and display battery voltage and cabin temperature. Very handy.