Alternator Whine Question

After driving some dusty roads last weekend (maybe coincidence, maybe not). I've got a mild alternator whine - loud enough to hear it inside the cabin at idle but not while driving.

I am sure it's the alternator. I replaced all idler pulleys today (didn't solve the whine, but the old ones were bad so good maintenance anyways), and when I unplug the alternator the noise immediately stops, and when I plug it back in it immediately starts again.

Question is - how long will an alternator whine for before going completely bad? Anyone have experience with that? I'm supposed to leave on a four day camping trip tomorrow. I actually pulled the alternator and blew all the dust out of it with compressed air, and the bearing feels smooth as silk. But there's nowhere local for me to get a new one before I leave. So I'm wondering if it's a bad idea to just run it for the next few days / few hundred miles and replace when I get back. It wouldn't be dangerous if it went out on me where I'm going, but it'd be annoying and expensive.

 

I’m not one to take advice from.
How far away is the camping trip?
How much driving are you doing?


I’ve seen them squeal like a pig and go for weeks.
And I’ve seen them fail with little to no noise.
You just never know.

What is ikely to happen-

If the alternator fails, you’ll get as far as the battery last.
If at all possible, I’d at least throw a “parts store” alternator in the truck with me, along with tools.



What you hope DOESN’T happen.
Alternator locks up, serpentine belt breaks, and takes out the front oil seal behind the crank pulley.(This does/can happen. The 4.0 is usually the one that this happens too)

 

Since you say it goes away when you unplug it it's likely a failing diode in the alternator, there's no way to tell how long it will keep going.
Best case if it fails it will just quit charging, worst case it will short out and kill the battery quickly or blow the main fuse.

 

I'd get it out of there asap, it could be overcharging the battery

 

In my opinion it’s the bearings of the alternator and not the electrical components. I don’t think your battery will be damaged. Now it might decide to bind up and break the serpentine belt but that’s even rare. The noise will probably just get so bad you can’t stand it anymore first.

 

Appreciate the insight - however if it was the bearing, wouldn't it make noise whether or not it was plugged in? The pulley spins regardless of being plugged in, and the noise goes away instantly if I unplug it.

 

Good to know. I actually have a voltage meter in the cigarette lighter and it's not currently over voltage while driving, but good to know that could happen

 

Sounds bad. Camping trip is a couple hundred miles, won't do any driving while I'm there (it's mountain bike trip). But I'm thinking I'll stop at my parents house and throw a new one in in the driveway on the way. Good excuse to buy one in Oregon and not pay sales tax.

 

Any idea what the output voltage is ? Does it whine more when putting a load on the system like when turning on the highbeams , rolling up/down the windows?

 

According to my cheap Amazon cigarette lighter volt meter, it''s putting out 13.6-13.7 volts regardless of what else happens. The noise does change when the AC cycles on and off, but the voltage doesn't seem to significantly.

 

When the whine comes and goes by disconnecting the field connector, diagnosis is done.. the alt is failing and needs to be replaced

 

Thanks, yeah understood. I fully realize that it's failing and needs to be replaced. My question is just how quickly it goes from "failing" to "failed". But it sounds like sometimes, it's a quick process and I should take care of it ASAP.

 

Something to you could try, might work might not. Use an air blow gun to blast the dirt out of the alternator. Do it with the engine off first so you’ll get an idea what will happen when you pull the trigger. Keep that in mind when you do it with the engine running. Hitting moving parts with the tip isn’t good. Worse would be stabbing a hole in the radiator.

Like what’s been already said, most likely time to replace it. If it fails on you, it’ll choose to do so at the worst time imaginable. Like when driving through a bad part of town late.

 

Thanks, yeah I actually removed the alternator and blasted it all out with compressed air. Tons of dust came out, but it still whines.

 

I'd suggest bringing the tools to replace it on the road. I assume that you'll have a route planned out; do a search along the way for parts stores, and start calling.

You can get the alternator out through the wheel well without removing the tire. Though removing the tire makes life a lot easier.

Good luck