Alternator running hot...

I have a 98 riviera that currently runs 15.3 volts from the alternator consistently. I have already replaced the alternator and it didnt fix it, great 160 dollar investment... so ne way, ive been working through this for the last week and my battery is good. Ive been chasing down ground cables, specifically the one for the battery, the one from my oil pan to passenger side frame rail, and both the cables to my starter. There was some crazy corrision on my battery ground and is snapped off the bolt for my ground from the engine to the frame cause it was so nasty. So those problems have been resolved and Im still running hot. Ive had people telling more horror stories about frying computers and other expensive stuff. Anybody have any ideas here or am I probably save running that voltage. Like is said 15.3 consistently and I have no idea how long it has been this way...

maybe a funky voltage regulator? most of 'em are built into the alternator, but I don't know about the buicks..

The voltage regulator IS internal, has been that way on ALL cars since the late 60’s or early 70's.
Normal output range for a 12 volt system is between 14.5 and 15.5 volts, if you are not getting any other indications that it is overcharging I wouldn't think 15.3 volts should be a problem. If you get a rotten egg smell in the car, meaning the alternator is overcharging the battery, then I would worry about it.
Are you checking the output with a volt meter or going by what the gauge reads? If using a true battery tester is it reading in the “HIGH’ range on the meter or the top edge of “NORMAL”?

nah 15.3 is wrong.

Glad you found us Greg! Did ya get my email?

Have you had your battery load tested? If the battery is dying, it might never be reaching system voltage and constantly trying to charge.

had the battery load tested at oreillys and i even took the battery out of my sisters grand prix and had it in there just to check everything out. same readings...thanks for the website, i like it.

Greg, did you replace the ground bolt?

I did on my Riv, I used a stainless steel bolt with the head cut off (cut it off with a Dremel MotoTool and cutoff wheel), that I cut a cross into the top of (also with the Dremel) and installed where the old bolt was. I drilled it out and tapped it 1/64th larger.

I used a couple stainless nuts on the bolt, jammed together, to make an assembly that looke pretty much like the old gorunding bolt. Even better, with the 2 nuts I could install the bolt then install the grounding wire under the second nut. So if I have to remove the ground for some reason it's not a PITA and I can leave the ground in place.

I also used conductive grease (available from Home Depot as "NOALOX") to lube the bolt where it screws into the frame.

Albertj

Yeah, it could be a poor ground, but I'm thinking more like a bad wire in the feed to the voltage regulator. Any corrosion on the wiring harness near the alternator?

Does the Riv have a wire hooked up to the S terminal on the alternator connector?

That is the Sense terminal and our alternators are capable of reading the vehicle voltage at that terminal. Some of the Bonne guys have added a +12V reference to that terminal. If your car already has a wire connected at that terminal, check it to ensure the voltage is not out of spec at say 10 or 11 volts. That may be a reason why it is pushing the 15.3

Hey albertj, i assume you are talking about your bolt trick for the cable from my oil pan to frame, that sounds like a good idea cause right now it have very janky extra cable that i ran to the bolt on my engine mount at the frame. thanks for that.

when i put the new alternator in i did not notice any corrision at the alternator end of the terminals but i did not check where the connections lead to, could you tell me what that sense wire is??

thanks alot. Greg

The sensing lead is the light blue one on the 3-wire connector to the alternator. It is connected to a thermistor in the battery compartment. At normal operating (battery) temps, the resistance on this wire "tells" the voltage regulator to output around 13.8~14.3v. If the voltage in the sensing wire is decreased by x amount, the output voltage increases by x.

I inserted a diode inline with my sensing lead, which hacks off .6v. This made my output voltage 14.4~14.9v. In your case, if the sensing lead were disconnected or the thermistor bad, it would see 0v. This might "tell" your voltage regulator to put out its max value. It's a long shot, but I would check the voltage of the light blue wire, with car running, to at least rule out the possibility.

Ok checked out my sense wire, the sense wire had 12.11 volts on it right at the plug into the alternator. So I see that you said i should be running at 13.8 to 14.3 volts, so 13.8 volts minus 12.11 gives you 1.69 voltage difference, if you take that 1.69 volts that my sense wire is not "seeing" and add that on to the 13.8 it should be running at and it turns into about 15.5, so it seems to me that that could be my problem, let me know if that theory makes sense.

so if that is my problem, and I already put a new alternator in there, it must be that my sense wire has some extra resistance somewhere. you said that the blue wire winds up in the battery compartment, so im assuming you mean under the back seat, im gonna go looking under there right now but if its somewhere else let me know.

Sounds like a possibility. It could be a bad connection on the sense wire upstream (toward the battery), causing increased resistance. I'll try to measure my sensing wire tonight to see what the voltage is.

This is a long shot, but are you installing the proper Alt with the proper pulley? Obviously an Alt for a gtp wont work well. Another thing to look into is pulley size. If your old alt had an overdrive pulley, and they reused this pulley, then your new alt would be overdriven too.

Oops looks like you found your problem,

I measured my sensing wire voltage output. It's right at 12 volts (11.4 with the diode in line). I guess it's on it's own circuit, not the same as the output to the system. Your 12.1 volts seems normal.

alternator was what i got from the parts store and the pulleys were not swapped. thanks for the idea but that should all be good to go.

yeah i was wondering, i think the purpose of the sense wire is to tell the alternator what voltage the battery has..

does anybody know if there is any other computer or device besides the regulator that controls the voltage output from the alt, or maybe some other input to the regulator?

The sense wire tells the alternator how hot the battery is.

What are you using to measure your voltage? My scanner tells me I have 14.4~14.9 alternator output, but my Fluke multimeter says 15.5v. I'll check it at other parts of the car. Maybe different at certain locations.

ive been using a cheapy cheapy digital multimeter i picked up at mernards, but ive also had it checked by two other devices, that a friend of mine has, not sure about what they were exactly but one of them for sure was some serious hardware, i could find out more if you think it might be the devices im checking with...