Voltage Gauge Reading 15v+

[misweetrevenge]

First off some info:
1991 GMC Suburban V2500 with 110,000 miles.

Question:
Volt gauge is reading pretty high. Is this bad? What would this indicate? Is the gauge reading off the Alt's output or is it reading at the battery?

I had the truck in the shop to get the suspension/steering/breaks inspected to get ready for camping season and they said the battery should be replaced asap. I haven't noticed any trouble starting or anything like that. Only thing i've noticed is my volt gauge reads higher than it was a year ago when the truck is running.

Any thoughts?

 

[4xcrazy]

A lot of times when my volt meters read that high, it was usually caused from a bad battery. The alternator is running higher output to charge what it senses as being dead, most likely a dead cell.

 

[clandr1]

Have you used a multimeter to measure the voltage at the battery terminal when the motor is running? Nominal reading should be 13.8v

 

[misweetrevenge]

A lot of times when my volt meters read that high, it was usually caused from a bad battery. The alternator is running higher output to charge what it senses as being dead, most likely a dead cell.

yeah that's what I thought. Thank You.

Have you used a multimeter to measure the voltage at the battery terminal when the motor is running? Nominal reading should be 13.8v

I'll go do that real quick and get back with the info.

 

[misweetrevenge]

With the engine running at the battery terminal the multimeter is reading 14.58v
Also, with the engine off but the key to the on position the gauge on the dash reads a hair under 13v

 

[4xcrazy]

Have the battery load tested.

We had some volt gauge weirdness on our most recent trip to SoCal in December. Gauge would jump up to close to that 15 mark, then drop down to normal, then down to around 9 for awhile.

Went to have it tested and was in fact a bad battery, bought a new one, all has been fine since. Standing voltage read normal, but when a load was applied to it, it dropped nearly dead.

Of course you're saying you you don't have any problems with starting, that you know of, you may be surprised what a new battery does to it.

 

[misweetrevenge]

Have the battery load tested.

We had some volt gauge weirdness on our most recent trip to SoCal in December. Gauge would jump up to close to that 15 mark, then drop down to normal, then down to around 9 for awhile.

Went to have it tested and was in fact a bad battery, bought a new one, all has been fine since. Standing voltage read normal, but when a load was applied to it, it dropped nearly dead.

Of course you're saying you you don't have any problems with starting, that you know of, you may be surprised what a new battery does to it.

Battery it is. Thanks for your help guys.

 

[Stomis]

I had this exact problem. Thought my gauge was wonky. Got out of the truck and heard the battery boiling! Battery was fine, internal voltage regulator was shot in the alternator. New alt fixed it up.

 

[misweetrevenge]

I had this exact problem. Thought my gauge was wonky. Got out of the truck and heard the battery boiling! Battery was fine, internal voltage regulator was shot in the alternator. New alt fixed it up.

Alternator is fairly new. But I'll check that out as well. I think it's simply the battery because the shop I had my truck in said the battery is dead. The thing probably has enough juice to start the truck and then the alt runs the truck. Thats probably why I'm seeing such a high voltage.

 

[Stomis]

Alternator is fairly new. But I'll check that out as well. I think it's simply the battery because the shop I had my truck in said the battery is dead. The thing probably has enough juice to start the truck and then the alt runs the truck. Thats probably why I'm seeing such a high voltage.

A properly functioning alternator should never break 14.7v as it is regulated. Pretty sure the older ones in these trucks only charged around 13-14v

 

[Blue85]

A bad battery has higher resistance than a good one, so the same charging current results in a higher voltage.

 

[4X4HIGH]

Normal voltage output from a properly working alternator is 13.5-15.5 volts but on average usually 14.5-14.7 volts. Once you start getting higher than 15.5 volts you start to overcharge the battery and it's life will be shortened in short order. The cause of a high volt reading is the internal regulator is bad/going bad.