Usualy when I have a charging problem it is not charging enough. I just got my 93 diesel. And I have been driving the heck out of it trying to find any problems. Today while driving the Radio blew a fuse. Thought that was funny and changed it. Ran about the same distance and blew again. I happen to look at the amp guage and it is right on the edge of the redline below 18 volts. I am guessing about 16 volt line. I was wondering if it is possible that the regulator has gone out of the alternator or some other problem.. Any Ideas??

I've seen an alternator overcharge and make a battery swell up and blow. If I remember right it was because the alternator was charging all of the time. I'ld watch your batts close.

Yes a regulator can cause an overcharge. It could also be caused by and internal alternator problem. The last thing is a battery/wiring glitch. I've seen overcharging from a wiring problem. The alternator wiring was being back-fed by a low voltage and caused the regulator to act like the battery was low and the alternator responded by putting out maximum volts. Remember, alternators are self current-limiting. The regulator senses voltage and regulates it. The current is regulated by the voltage applied to the stator (field) circuit.

If I remember right, batteries are meant to handle more then a 12volt charge, perferably..13.3volts minimal and up i think.
we have a C20 1988 surburban here. charges the same way yours does, right below redline. always has. no problems at all with it.
I think it depends on belt tension, and the amperage rating on the alternator.
your alternator shouldnt be the problem.

Put a digital multi meter on the battery while engine is running. You should see no more than about 14.5-14.7 volts MAX. If you are exceeding remove alternator and have it tested, this will show whether the alternator is the problem or it is wiring related.:cool: :grd:

A fully charged battery should read 12.6 volts.

If your batteries are in good condition and you don't have a short someplace then your alternator will put out 14.7-14.8 volts for a short time after startup. It should then taper down to about 13.8 volts. If everything is good and the unit continues to put out 15 volts then I would replace the alternator to keep from ruining the batteries. I had to replace mine 3-4 years ago due to overcharging. I got it verified at Autozone and it was replaced under their lifetime warranty. That unit was replaced last year due to the noise suppressor circuit failure so I replaced it under the warranty. I believe in those lifetime warranties!!!!

I fianlly got some time this weekend and changed the regulator and it made no diffrence. Man I hate to give up on this alt, the berrings are still tight. I am wondering if the guage is bad. I checked the wiring and it appaers to be working properly.. What else in a alt can be replaced??

Check the voltage with an external (known to be "good") meter. This will verify your guage. One small internal glitch with replacing the regulator is where the diode trio attaches to the rectifer bridge. If the tabs on the trio get bent just right, they have been known to touch the bridge and cause the alternator to "full field". Result: overcharge and no regulator control. This problem is rare and will cause extremely high voltage readings and a very hot (to the touch) alternator. Readings can be as high as 16 - 17 volts. Things won't last long if this problem occurs. Just something to check.

If you have the alt apart, check the diode trio and the rectifier bridge with an ohm meter to make sure all the diodes are good. Measure ohms across each leg of the trio, reverse the leads on the ohmmeter and check them again. One way, the meter should read infinite resistance and, when reversed, it should read zero ohms. Usually diode problems cause low charging voltage but it's something to check while it's on the bench.

I buy lifetime warranty alternators, starters, fuel pumps, hydo assist units, power steering pumps, etc. I have changed out alternators for failing to taper the charge down as well as the noise suppressors failing. 40-50 years ago, the bearings would go out, but it has been over 20 years since I had a front bearing go out. And when we had generators then we had to change the brushes before anything else failed.