Does an ATF leak onto the alternator cause it to fail? Can we test if this is true?

Q: Does an ATF leak onto the E39 alternator cause the alternator to fail?
Q: Can we test if this is true?

Cn90 questioned the existence of the alternator bearing Chinese PSF torture in this thread today:
> E39 (1997 - 2003) > Alternator Replace 2003 530

Originally Posted by cn90

Contrary to popular belief, ATF leak (from PS reservoir) has nothing to do with alternator failure. The alternator dies at 150K, give or take, even in cars with no PSF leak.

Originally Posted by cn90

I don't know why people keep saying ATF kills alternator! There is simply no proof for that.

When you think about it, millions of Auto Transmissions or PS systems have ATF in there and it is the ATF that lubricates the bearings etc.

So, this thread is opened to ask 'what tests' could the next person who replaces their alternator perform which would give evidence, either way, of whether or not the power steering fluid leak is or is not torturing our alternator bearings to death.

Note: Picture is from a cn90 DIY on fixing the hoses.

The bearings are sealed and also relatively inaccessible from the outside. I wouldn't insist that they are not going to get a drop or two of PS fluid on them but I'd venture most if any PS fluid leaking from the reservoir onto/into the alt housing will be flung outward by the spinning stator.

I think it -would- be possible for stray fluid to short the regulator or across the slip-rings, if it's conductive, but my understanding of electricity is fairly poor. If the graphite brushes and slip-rings are contaminated, what happens?

PS fluid-induced or not, if the bearings were dry enough to cause the alt to fail, they'd probably create a decent amount of noise well in advance, or at least enough that someone within earshot would know something bad is brewing.

Originally Posted by pleiades

if the bearings were dry enough to cause the alt to fail, they'd probably create a decent amount of noise well in advance, or at least enough that someone within earshot would know something bad is brewing.

This horrid noise, I can attest to!
I had that screaming noise (loudest at startup for the first few minutes) 'brewing' for six months before my alternator finally failed
- Video of cold idle engine squeal (1)


At the time, I had attributed the noise to the Chinese water torture of the bearings (only with ATF instead of water) ... but now ... with information from you and cn90 ... I'm not so sure.

I guess we should look at WHERE the bearings are, in relation to the PSF drip, to see if fluid 'can' even get to them in normal use.
(picture from cn90 Bosch alternator rebuild DIY)

The original question seems to be "Does an ATF leak onto the alternator cause it to fail?" and can we test if this is true or not?

Simply determining the cause of any component failure can be very difficult, if not impossible, without a thorough autopsy to determine the true cause of component failure. Linking the cause and effect of two separate events (ATF leakage and alternator failure) is even more difficult. This thread applies to alternators that have failed because the bearing has failed. While failed bearings may be a common cause of alternator failure, it is not the only one. See this for the many possible causes for alternator failure: http://www.ehow.com/about_5422984_ca...r-failure.html Hence, before testing if an ATF leak is causing a bearing failure (or possibly some other problem), you must verify that a bearing failure has even occurred (which might not be so easy).

Before trying to establish a test for cause and effect, it may be better to establish some evidence of linkage between the events. Keeping in mind that this is all based on anecdotal data provided on the internet, I think a better approach would be to survey forum members to determine who have had an alternator failure and who have had an ATF leak. Then determine how many had an ATF leak followed by an alternator failure. If the number of ATF leaks is large relative to the number of the subsequent alternator failures, I would believe that the likelihood of a linkage between these events is small rendering the need for a post-mortum test to be low. I for one have had an ATF leak but have not had any alternator issues.

+1 ^

I hate to admit it, but I drove my car for 6 months with a bad PSF leak at the reservoir and it did not affect my alternator. I was close to 200K so I put it off. Eventually I hit 200K and replaced all hoses under the hood.

remember that transmission fluid (what's in your PS reservoir) is not so much a lubricant than it is a pressure medium. It mostly keeps seals supple and creates pressure throughout the tranny. Same in the PSP. I think it is very possible that it could wash out whatever is lubricating the alternator- whether it be a packed grease or oil. Just saying that there is a vast difference between ATF and oil or grease. Don't mix and could see PSF drying out a seal made of a material looking for a higher petroleum content lube. Most likely would do so when car is sitting over night.

Originally Posted by Fudman

The original question seems to be "Does an ATF leak onto the alternator cause it to fail?" and can we test if this is true or not?

I just corrected the title to indicate that.

Originally Posted by Fudman

it may be better to establish some evidence of linkage between the events.

OK with me for us to use whatever data we have at our disposal.
The goal is to think critically about the cause & effect.

Originally Posted by Fudman

determine who have had an alternator failure and who have had an ATF leak.

Add one to the anecdotal evidence as I certainly had a PSF leak when my alternator failed suddenly.

The funny thing was the alternator spun by hand only slightly roughly. I didn't even know, at the time, where the bearings were so I can't state their condition. But the alternator did fail all three tests at Autozone, so, if it 'was' the bearing, perhaps the heat had secondary effects.
(PS: Ignore the caption below; I'm re-using my photo.)

Originally Posted by 540iman

I think it is very possible that it could wash out whatever is lubricating the alternator- whether it be a packed grease or oil.

So, 'if' the PSP ATF leak 'is' causing the bearings to fail, is 'this' the suggested mode of ATF-induced failure?

Originally Posted by bluebee

0. Bearing is lubricated with thick grease which is designed to stay inside the race and stick to the balls
1. Power steering fluid slowly seeps out of the hose connection and collects on a bend, where it eventually, and slowly drips on the bearing, like a Guantanamo-Bay water torture ... very slowly solubilizing and dissolving a bit of the thick grease (each seeping drip being perhaps an hour or five apart)
2. This solubilizing and slowly washing away of the packed-in grease happens slow drip by slow drip (maybe three or five drips in a day?) so it takes a year or two to completely wash away the grease
3. Over time, the grease is gone (so the theory goes) and all that is left is a bearing lubricated by one to three drips of power steering fluid in a day.

I think the best way to determine if the hypothesis is correct or not is to autopsy a bearing on a failed alternator that was subject to ATF leakage to determine if the bearing has seized or not. Doing multiple bearing autopsies will certainly give us the evidence we are seeking.

I'll offer up my alternator if and when it fails!

Originally Posted by Fudman

I'll offer up my alternator if and when it fails!

As will I.

But I highly doubt ATF can seep directly into these DOUBLE sealed bearings.Over the past year I have bought the front and rear bearings, will be buying the brushes and maybe the regulator for a rebuild.

I can tell you that having ATF seep into these double sealed bearings, while possible, is very difficult. Your voltage regulator or brushes are more likely to go before ATF causes two seals to fail allowing the grease to leak and then seize the bearings.

I had the PS hoses leak, no issues with the alternator. However, when I removed the alternator to service it, there was absolutely no trace of any kind of fluid on it.
The leak was dribbling along the hoses and dripped on the steering rack - driver side. From there it pooled inside the splash guard towards the rear.
Never had a drop on my garage floor. I believe most of the ATF that leaked inside the pan, was lost during driving.

I doubt the ATF degrades the alternator at all, main failure I think is normal wear out of brushes.

Not saying this is how all alternators fail or even that all have the hose routing that would allow ATF to hit the alternator just right-I'm saying that it seems plausible rather that to dismiss the notion entirely as beyond the realm of possibility. Don't know how much time I would devote to "wondering", but if we are again playing the "what if" game, I guess it's possible. Once I can wrap my arms around "what is reality" I might move on to this one. Until then, the serenity prayer still drives my actions...the accept the things you can not change, change the things you can blah blah blah.

For the record, this question (of what fails on the alternator) came up again today over here:

Originally Posted by bin01123

bluebee,

So would you say the alternator is a part on the BMWs like the radiotor? Its just bound to fail sometime after 90k. I'm asking because I'm at 94k on my 540 and just completed my cooling system overhaul. I was looking to see what the next part is I should replace before it fails.

Originally Posted by bluebee

I had asked a similar question to ascertain WHY our alternators fail:
- Does an ATF leak onto the alternator cause it to fail? Can we test if this is true?

And, of course, I've asked how to TEST a failing alternator:
- DIY how to test a BMW E39 battery & alternator (discussion)

The answers that came back weren't exactly conclusive, so, I can only say that we'd really need more data on what fails on the alternators most:

a) Is it the bearings?
b) The diodes?
c) The regulator?
d) The coils?
etc.

Anecdotally, I'm guessing that most failures are the bearings. If that's the case, then I'd recommend you stock the bearings yourself, well ahead of the time your alternator fails. Luckily, they use standard-sized bearings, so stocking these $5 parts would be easy.

Then, when your alternator finally does fail, you can take it apart and replace the bearings quicker and cheaper than you can if you order a rebuilt alternator (which is what most of us do when faced with the sudden failure).

See also:
- How to test your generator (1) & how to determine exactly what alternator you have (1) & a DIY for replacing the E39 I6 alternator (1) (2) (3) (4) (5) or E39 V8 alternator (1) (2) (3) (4) & why you want to clean out the air-cooled alternator air duct & cooling vents (1) (2) (1) (2) & why rebuilding an alternator is preferable to replacing (1) & cn90 DIYs for rebuilding a 1998 air-cooled BMW Bosch alternator (1) (2) or his VW Bosch alternator (1) & cdawg246's quest for materials for a Bosch water cooled alternator rebuild (1) & Aioros' 1999 Valeo Alternator rebuild DIY (1) and his quest for materials (1) & Cn90's explanation of where to get hard-to-get alternator rebuild parts (1) & how to tell from the part number if a replacement alternator is actually rebuilt "by" Bosch (1) & a DIY for replacing the brushes in an (Audi) Valeo alternator (1) & a Bosch alternator bearing replacement from a 1997 MB S600 (1) & from a Range Rover (1).