[reinhardtsearay]

Hello 91 coupe with 70000 mi started hearing a whinning sound from my altenator. when you first start it up you can hear it pretty good then it goes away . Should i swap it out or run it for a while longer ? I sounded it with a dowel rod so i know that is where the noise is coming from. Any suggestions guys ?

[Slicktop]

Alternator noise varies with load. The more it has to work the more its diodes make noise. When you first start up the car the alternator has to recharge the battery which puts it under load. Also,when the alt is under load it puts more strain on the serpentine belt which can cause noise, check the wear indicator on your belt tensioner.

As long as the alt is charging ok I would just keep an eye on it after checking the belt.

[vettex2]

since it just started whining , diodes are probably going or gone

[Slicktop]

Wrong, if the diodes were gone it would not charge ............

[BSenzina]

OK.....based on a previous response I am a littel worried......before I replaced my battery, I had to jump off my 84 a couple of times......I heard NO whinning.......should i be concerned???

[vettex2]

Originally Posted by Slicktop

Wrong, if the diodes were gone it would not charge ............

WRONG
it charges AC instead of DC
and
sometimes they don't all go at once

[Vettemagnet]

Originally Posted by reinhardtsearay

Hello 91 coupe with 70000 mi started hearing a whinning sound from my altenator. when you first start it up you can hear it pretty good then it goes away . Should i swap it out or run it for a while longer ? I sounded it with a dowel rod so i know that is where the noise is coming from. Any suggestions guys ?

You can have it tested at auto parts places like Advanced Auto. It's on it's way out, hence the noise. Who cares if its a diode, there not supposed to make this noise

I personally wouldn't trust it, because it will fail when you really don't want it to. Murphy's Law.

[toobroketoretire]

Originally Posted by vettex2

WRONG
it charges AC instead of DC
and
sometimes they don't all go at once

Correct answer. An alternator puts out alternating current then the rectifier changes it to direct current by using 3 one-way diodes that block 1/2 of the sine wave. Usually only one diode will fail and that will cause a 33% reduction in maximum output. All alternators will whine to a certain extent and the bigger the load is the bigger the whine is. You could either have a bad diode trio or a bad rectifier. Both are very inexpensive and can be purchased from any auto parts store

[fishslayer143@yahoo.com]

Originally Posted by vettex2

WRONG
it charges AC instead of DC
and
sometimes they don't all go at once

yep,

[Slicktop]

What I orignally said is absolutely correct and needed no out of text comments:
"Alternator noise varies with load. The more it has to work the more its diodes make noise. When you first start up the car the alternator has to recharge the battery which puts it under load. Also,when the alt is under load it puts more strain on the serpentine belt which can cause noise, check the wear indicator on your belt tensioner.
As long as the alt is charging ok I would just keep an eye on it after checking the belt."

Also, brand new diodes in alternators make noise so to say that one is failing because it is making noise is stupid.....