Mystery Alternator...not sure if there really is a problem

[rfdude]

I have read countless alternator threads and have not seen anything similar to what I have been experiencing on mine. Hopefully I can get some help to point me in the right direction. Here goes:

The vehicle has 220,000kms on it. Not sure if its the original alternator as I just picked it up about a month a go from a dealer with no history on it. Alternator lights intermittently comes on 1-2 times a week. I have been able when the light is on, check the voltage on the vehicle with my fluke dvm, measuring at the block in the engine compartment. It is showing 14.2v and when the ac kicks in a drop to 13.2 then comes back up to about 13.6 until it shuts off then back up to 14.2v. To me this is normal. As my wife drives it mostly she is paranoid all the time of it dying on her. I have taken it to my work which is about 100kms to work and have even drove it the full way with the alternator light on and when I got home checked the voltage I get the same results as shown above. Shut it off after the drive and turn it back on and battery shows absolutely no sign of not being charged???? So with this happening I am really not too big on changing the alternator out for the sake of "just to be safe" when we have experienced absolutely no signs of the alternator not charging.

Does anyone know if its the alternator voltage monitoring or the current output that turns the dashlight on when low? If its the voltage at what voltage point does it illuminate it and where is that point where it is being pulled from (front off of the alternator or back at battery)? Im wondering if there is corrosion at this point and is providing a false reading to the dashboard causing the light to go on....? Am I on the right path or just bite the bullet and change out the alternator?

Any help would be appreciated.

thanks in advance

[jspdr]

All i know is how to test for bad alternator. let the engine runs, carefully remove the negative battery terminal, if engine stop running, then you have a bad alternator.
Good luck

[epdarks]

Try some smaller fixes before changing the alt, but they will all need them eventually.

Maybe your sensor that reads voltage is bad? Sounds like the alt is charging the battery.

Have you considered taking it to a shop for a diagnostic?

[rfdude]

you mean a load test...no but likely should. I just thought there just might be a common problem that points to the alternator but really isn't the alternator (likely just wishful thinking). I've read too many threads that indicate after replacing their alternator the problem reappears again. I really don't want to become one of those guys that become an expert on re-re alternators on an X5.

[epdarks]

I would buy your wife the beast towing coverage money can buy, then just wait until the alt dies

[rfdude]

lol, she has that already and has already used it when she ran out of gas because the gauge was not working accurately (she is not impressed so far with BMW coming from a bulletproof Audi). I fixed the gauge but she is still warming up to the BMW.

[rfdude]

thanks jspdr will try that. BTW, why does BMW make it so difficult to get to the silly battery???

[TwinTurboGTR]

It sounds like a voltage regulator problem. They tend to go bad on the water cooled Alternators or generators.

If you think about it, how many time do you NEED to get to the battery? Once maybe every 3 or 4 years? No room in the engine bay for it. Don't want it taking space up in the trunk. I guess the engineers see it as a part that rarely needs to be accessed, so they hide it. lol My Audi was the same.

[rfdude]

good point twinturbogtr on the battery. Unlike Audi though (got one) they don't make you take your tools out to get at it!

I read up on the regulator issues on this forum and see them on ebay that you can just buy the regulator for ~$90. I do have the Bosch alternator and heard if you are going to replace/repair best to stick with Bosch.

[TwinTurboGTR]

Yeah stick with Bosch. Are they really $90? If you check harder, I think it can be had for $60.

As for the battery, IIRC correctly, you needed a 10mm socket to unbolt the 4 nuts securing the battery strap! lol! So you do need tools lol