Strange events with new alternator - ideas?

[aatos]

My battery light on the 2002 4.4 came on a few weeks ago - checked voltage with engine running - about 11.5. I bought a refurbished Bosch alternator on-line, installed it, and the light went away, voltage is around 14.0.

But now, if I run for quite a while, turn off the engine and restart, the battey light comes on again, and stays on until the engine is turned off and has time to cool down. If I'm driving and don't stop, the light doesn't come on. Or if I drive only a short distance, stop and restart, no ligght. Seems to be a problem related to heat build up, and only if I turn off the engine and then restart. Very hard to get gas this way.

Any experiences like that? I would suspect the regulator on the alternator, but here is no problem if I just keep driving, so I don't know.

[blktoptrvl]

I think I would get a cigarette-lighter voltmeter/recorder (I wonder if there is a phone app for that?) and keep a chart of the voltages under all conditions you mention and see if a pattern emergres - or if it is ever in a very low or very high charge state and go from there.

[Skyline]

I have not owned a BMW for a long time until the current X5. But in the past, I owned many different ones. And I had nothing but bad experiences with rebuilt alternators. Especially from parts stores. I'm convinced that on many of these, the definition of rebuilding consists of a fresh coat of silver paint, and that's it.

Do not assume your freshly rebuilt alternator is good. Confirm its performance before looking for other problems. Perhaps a VOM with an amp probe could tell you how it's doing.

[TiAgX5]

Did you load test the battery?

[aatos]

I had a chance to do a 120 km round trip, mostly highway, yesterday, with a voltmeter hooked up through the lighter. On the way out voltage was consistently 14.05 or thereabouts. When I went through a very slow section of town voltage suddenly dropped to 11.5 and battery light came on. After a long stop, on the way back, voltage read about 13.9 all the way, with no stops.

[aatos]

Originally Posted by TiAgX5

Did you load test the battery?

I've tried two different batties, one of which is definitely good. Same issues.

[aatos]

Originally Posted by Skyline

I have not owned a BMW for a long time until the current X5. But in the past, I owned many different ones. And I had nothing but bad experiences with rebuilt alternators. Especially from parts stores. I'm convinced that on many of these, the definition of rebuilding consists of a fresh coat of silver paint, and that's it.

Do not assume your freshly rebuilt alternator is good. Confirm its performance before looking for other problems. Perhaps a VOM with an amp probe could tell you how it's doing.

I'm not assuming anything at this point, just trying to find the problem. Somewhere I read that the computer will shut off the alternator if voltage gets too high, to protect itself. Anyone else heard of this? If the computer can shut off the alternator, is it possible that is what is happening? It still seems like a temperature issue to me, whether in the regulator or the computer (or a temperature probe?)

[subieworx]

Sounds like the alternator. I have heard of some issues with rebuilt bosch units in the last year. If not that it could also be the positive battery cable. E46 3 series have some issues with the battery cable rotting out over time. The cable builds up a lot of heat at a connection near the battery that causes the light to come on.

[Skyline]

Did this refurbished Bosch alternator come in a Bosch box or a plain cardboard box? Exactly who rebuilt this? It is certainly suspect from the symptoms.

One other thing I would try, is to get one of those battery post cleaners. Use the cone shaped brush on the cables, and the post brush on the posts. Them make sure you get the cables on tight. Tap them down with a small ball peen before tightening so you get good contact. I'd also clean and resecure the connections to the alternator.

[Chopper]

Sounds like the alternator, dealt with Bosch in the past and a few faulty straight out the box new !

If its been refurbished and you think it's a heat related problem, it sounds like a bad connection or dodgy soldered joint, as the alternator heats up it expands the connection breaking the contact = light on

Although did you test the old alternator after it was hot ? And get 11.5v as did refurb through town, could be bad pin in plug or bad signal wire, sorry I'm not familiar with connections on the alternator mentioned

If you stuck old alternator back on and tested it on motorway it might prove this

Hope this is some help