My volts gauge on the dash has been reading at 13 volts ( i assume each little line is 1 volt?) when i first start the truck and its cold. as the motor gets hot or if the day is 90 degrees outside the gauge goes down to about 11 volts or 10.5 with the A/c on.... why? and on a cool day out like 70 degrees the guage reads close to 14 and really doesnt go down when it gets to full operating temperature. what dow you think is wrong? i had the alternator rebuilt about 2 1/2 years ago and it was reading 15 volts back then when i put it in the winter.... any help greatly appreciated

 

if you have a volt ohm meter i would check it against what the factory gage say's its putting out.

If its still reading low clean all the terninals at the battery and make sure you have a solid connection at the alternator.

hope that helps

 

yes i have one of those cheap yellow volt meters. should i check the volts at the battery cables? and should it be running right?

 

As you observed 15v first thing in the morning in winter is not uncommon. The alternator has an internal regulator and is also temperature compensated. That means as underhood temperatures rise the charging voltage drops, so the dropping voltage is normal. It does seem low though, confirm your voltmeter with another one and get your battery tested. It may be sulfated and placing a constant draw on the charging system.

 

ok tested it. with the motor off, the battery and at the alternator both read about 12.20 volts. but the inside dash gauge reads on the first small line which i think is about 9.5 volts. then i started the truck and reads 14 volts in dash and 14.40 volts at the battery and aternalter. then i put on the a/c all the way and got 13.98 volts at battery and alternator. but the gauge read 2 lines below the 14 mark. now thhe motor was hotter to. so then i left the a/c on and put on all the lights and got 12.98 at the battery and alternator. but the dash gauge read on the first large line which i guess is 10 volts.... so i turn the lights off and it reads 13.98 again and the dash gauge went up only 2 lines....so what you think is going on here? will i eventually get stranded?

 

I'm trying to figure out the same with my 92. With just the engine running and ac on 4 the volts drop to in the 12's and the lights dim and idle drops low like the engine is struggling. And let's just say it hates my amplifier...

I'll let you know all the things I've checked while having this issue.
Make sure the serpentine belt isn't slipping and the belt tensioner is in allignment and doesn't move while driving. Check all your grounds for loose connections and check the wires for corrosion. If you hadn't already, replace your battery ground to frame ground with 4 gauge or so. Even if not running a stereo system or anything it can do wonders.

Maybe have your battery tested. I'm having the same problems and my battery shows a charge of 12.6 when the engine nots running. I'm going to have mine tested and maybe swap in another one just to make sure. I've seen batteries show a good charge and then be the source of the problem before. Good luck and if you find out anything keep us updated!

 

Make sure your terminals and connections are clean and tight. Man, if it runs OK I really wouldn't worry about it. If it still bothers you, pull the alternator and have it checked. Most A/P stores will do it for free.