Help on a E39 2003 water cooled alternator

[Jslininger]

I have read a bunch of post about the water cooled alternator on my Bimmer but I still haven't found an answer. Here's my problem.

2 months ago I was driving and it started acting up. I turned around and limped it back to my home town. I just made it into town and had to park it because it was about to die. The Battery was about out of charge. I don't remember if the battery indicator light came on or not. i could just tell it was going dead and the alt was not charging. (went to limp mode, then 5 more miles light shut off)

Next day I got it charged up and ran it back to my place. I checked out the output of the Alt and it was under 12 volts. So I ordered a rebuilt one.

I got my new one and when my son was removing the battery terminal he started with the positive and grounded it for a second. Well I checked out everything and I didn't find anything wrong with the battery or any fuses. (I wanted to put this in here just in case but I don't think it affected anything)

OK I just went about changing out the alt. Got it swapped out and started it up. Still less than 12 volts and that is just running off the battery. Read on here that many times alt come bad so I sent it back and got a new one sent. I just got done putting that one in and it is the same deal. At the Battery I have 11.7 when running and 12.8 when I shut it off. I did look at a couple fuses and they were all good.

What is the best way to start looking at the wiring before I pull this one out and send it back. There is two lead wires at the clip that plugs into the Alt. What and when is the voltage at those wires? I live in a small town and the closest BMW dealer is 300 miles away. With it being a water cooled alt no one can test it locally. I did check the output right at the alt when it was running.

I have checked the connection on the Alternator and they are good, along with the battery connections.

[sienayr]

I can't help with the wiring, my suggestion if at all possible would be get it to a parts store and have them test the system. At least then you'll know for sure if the alt is bad. They may not be able to test the alt on the bench but should be able to hook up the charging system tester which will pinpoint bad alt, bad battery, etc.

[geargrinder]

Worth adding that jicaino suggested bench-testing the alternator with a simple cordless power tool (drill/impact) spinning it up to 600rpm or so.

I'm not sure why shops say they can't test this on the bench unless it's related to not having the right mounting jigs, but if its because they think it needs to have water on it to test, that's silly, its a normal alternator inside and wont' assplode from just a brief test run.

[JimLev]

Usually they only have the capability to mount alternators that have the 2 holes that are used to mount and provide tension for the alternator belt. That's what I found out when I took mine to Autozone years ago.

[sienayr]

Usually they only have the capability to mount alternators that have the 2 holes that are used to mount and provide tension for the alternator belt. That's what I found out when I took mine to Autozone years ago.

Correct, I went around to several parts stores (AZ, Advanced, O Reilley), and none could mount it. Finally NAPA was able to mount it, but... they didn't have the right plug adapter in store. So then I called every NAPA store in town and none had the right adapter. I finally ended up at at a Bosch authorized service center that typically services very large alternators for trucks and such. They tested but couldn't get the part to repair it and sold me a new one (PowerSelect I believe).

Times like that I miss my Hondas and Toyotas. Until I get back behind the wheel, of course.

[Jslininger]

Yeah if I can't get anyone to test one here I am just going to take my old one an put it in a vise. Use the idea of the drill to spin it then slowly add some smaller voltage to it to see what happens. I have read on a different BMW it went up to 8VDC and that would be put out the normal 13.8VDC. I figure if I use a five smaller batteries (D size) it would get up to 7.5VDC. That should put out something close. But first I will run out to a couple parts places and see what they can do.

On Ebay they do sell the parts to rebuild the alternators. Just search under Bosch, I found everything from the complete kit to the individual parts.

[jicaino]

Now I'm doubting my recollection... I think the water cooled alt. Is self exciting. Think. I don't Remember how I tested it, I think I recall having spun the shaft and measured ground to the casing and (+) to the big fat cable terminal

[Jslininger]

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Well good news is i found the alternator schematics the bad news is my alternator is fine. I guess this weekend I will be chasing wires! Thanks for the help so far!

[sienayr]

Well, at least you (hopefully) won't have to drain the coolant out again! Good luck with it.

[geargrinder]

Good progress at least. Good luck w/ next steps and report back if you fix it.

[jicaino]

Sorry to hear it's not the alternator. You'll be in for major headaches.