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Discussion Starter · #1 ·
Hey guys!
Unable to find ANYTHING on this (which is really rare these days) so I wanted to ask for some help. I have a "squeal" that a mechanic buddy told me was from a worn bearing in my alternator. Here are the symptoms I am currently experiencing.
When the car first cranks (cold engine), the engine bay squeals pretty loudly. When the car accelerates through the first few gears and the car warms up the car squeals at different pitches (apparently because a different electrical load is placed on the alternator as the car shifts gears.) Once the car warms up, this noise disappears altogether.
I thought at first that the noise was due to worn belts or a loose pulley, but the alternator bearing also seems feasible.
Does anyone know which alternator I would need for my 2005 BMW 330i? I see two different part numbers that fit my vehicle: 12-31-7-519-620 and 12-31-7-501-599.

Without taking the alternator off entirely, is there a way to determine the specific part number?
 

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Its your tensioner pulley and your idler pulley.

Alternator pulley never ever breaks on these cars. The alternator itself will burn up way before the pulley does.


Sent from my X10a using Bimmer App
 

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You need to remove the alternator to find out which plug style you have for a direct replacement.

While your tensioner pulleys are more likely to fail, alternator bearings can and do fail. Theres two bearings on an alternator and either can fail. See if it spins freely with the belts off.
 

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If it's a squeal I would think it's more of a belt issue, which points to tensioners or a bad belt. What have you replaced so far? Maybe give us a recording of the sound?
 

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Have replaced pulleys - still hear whirring noise on cold start

Have the same issue as the OP ('04 325Ci). On cold start there's a whirring/squealing noise - in gear, higher revs increase the pitch of the noise.

I've replaced the idler pulley and the tensioner pulley, and the A/C tensioner was already new so did not replace.

My thoughts is that the alternator bearings are dry? Is this possible? Do folks usually just buy an entire replacement alternator or is it DIY to replace/regrease the bearings?

Thanks for your help!
 

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I did replaced my alternator bearings few weeks ago! the big bearing was good but smaller was not! and it did not solve my high pitch noise! to do a test, take away air condition compressor belt and main belt away! than start engine for a minute! there will be no PS, WP and Alternator spining so You will see is there any noise like previous situation! just to be sure if it is alternator! Also alternator is fairly easy to remove from car! I can do it now in less than 20 min :)
 

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@grimma - that's a good idea! Where did you get your bearings btw? And I've read you need a press to re-enclose the bearings?

I'm wondering, if it's not the pulleys, and not the alternator bearings, what might it be? Perhaps a belt alignment issue?
 

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yes you need some standard puller extractor tools ! search forums for DIY! also check first what is your alternator type, valeo , bosch etc. I had also disolder and solder my rectifying unit 6 connections! I am in europe so where do I buy my bearings doesnt help you to much! but once you have a god information about alternator and some tools it is not difficult job at all!
 

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Replace your battery. When cold, the alternator will start charging your half dead battery, putting large load on the alternator, making the belt slip - squeel.
 

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My 03 325ci just started doing this same thing. Here's the kicker. It was doing this in Oct. I replaced the alternator as a mechanic told me the alternator was not keeping the battery charged. Well. I get new alternator. Car runs fine for a while. No squeal. Now. Last night. Same Squeal. On the new alternator. :/ Do I get a new battery now? The center yellow light and brake light in yellow are on which other threads have said were from a bad battery. Maybe the battery is bad?
 

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Flame suit fastened:

I have a different theory than most people on belt squeal, that it is a result of too much friction in the pulley/belt interface. I have SOLVED several chronic squeal problems by spraying armor all on the belt. I know people will tell me that this may cause the belt to slip but I have never seen it happen and I have sprayed belts many times, both v belts and flat Serpentine belts. Belt dressing sprays are more of a resin that can make the problem worse.

Trust me, there is plenty of tension on the belt, it will not slip.

If the sound immediately goes away when you spray it the squeal is not the the bearing.
 

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Just remove your air box and look at the markings on your alternator to see which one you have. Disconnect your connector too. Verify if it is rectangle or oval.

Could your WP be making noise?


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