[bimmer777]

OK, so the battery light went on recently and of course my alternator was the culprit (car died after a while). No big deal, car has 53k miles, about time. Read a ton of threads on here on alternators and decided to go with the Bosch rebuild unit. In one of the threads I noticed a good price offered by Custom Performance Innovations so I gave them a call to make sure the units are in fact rebuilt by Bosch. I was assured that the rebuilt units come straight from Bosch and that they carry a 2 year warranty so I ordered.

I received the alternator and changed it myself after reading the DIY on this forum. Swap went flawless, took me 1 hour altogether. I decided also to order a new Optima Redtop battery since mine was drained and was the original battery in the car (6 years old).

Results:
Battery light is off while the car is cold but goes on when engine warms up to normal temperature. Actually I noticed that battery light goes on after the Oil temp gets close to 210 so it takes a while.

Belt is routed correctly.

Voltage reads 12V when car is off. When on, voltage is 14-15V.

Car does has not died after driving and restarting numerous times.

Questions: it looks like the alternator is working but might be overcharging a bit (is 14-15V normal when car is on)? Would the battery light go on if alternator was in fact overcharging? Can this be a faulty voltage regulator? What else can the problem be? Would love it if Don (deilenberger) would chime in.

[deilenberger]

Normal standing battery voltage (no load) is 12.6V - if you're reading 12V, something is wrong, and my WAG is the battery isn't fully charged. It is a VERY GOOD THING to charge a battery at least overnight before installing it. Installing it with less then a full charge means it will never have full capacity.

Most alternators charge around 14.3-14.6 volts - so the output is fine, but is the output still at that voltage when the red light comes on?

I'm guessing not - and I'm guessing the rebuild was defective or you have a wiring harness problem. Can we assume you cleaned the connections to the starter carefully before hooking them up? If not - do so.. If it continues my money would be on a defective starter. FWIW - rebuilt Bosch starters - rebuilt by Bosch - normally come in a brand new box and look identical to a brand new starter.

I'll just add - the failure mode isn't a surprise. The starter you got was rebuilt because it was failing on someone elses car. It sounds like a thermal fault where some component or wiring is breaking down or opening when the alternator gets hot enough. That wouldn't show up during rebuild testing since I'm certain they don't heat the starter up to check for this sort of failure as part of the QC.

[daytonaviolet]

did the OP install a starter too

Originally Posted by deilenberger

If it continues my money would be on a defective starter. FWIW - rebuilt Bosch starters - rebuilt by Bosch - normally come in a brand new box and look identical to a brand new starter.

I'll just add - the failure mode isn't a surprise. The starter you got was rebuilt because it was failing on someone elses car.

[pachieh]

He didn't install a rebuilt starter, he put in a rebuilt alternator. I'm not banking on the starter as the root of the problem because once it starts the car, it isn't used anymore. I'd look at the alternator relays or alternator wiring itself. If your car is starting just fine, then your starter is fine.

[deilenberger]

Picky picky picky.. make one little mistake..

/codeon
Replace all references to "starter" with "alternator" above
/codeoff

OK - happy?

[pachieh]

Originally Posted by deilenberger

Picky picky picky.. make one little mistake..

/codeon
Replace all references to "starter" with "alternator" above
/codeoff

OK - happy?

Yes yes...

Clean the lead with a wire brush and put some dielectric grease on it before you reinstall it.

I agree that swapping the voltage regulator as a last resort is a good troubleshooting effort.

Keep us posted.

[deilenberger]

Originally Posted by pachieh

Clean the lead with a wire brush and put some dielectric grease on it before you reinstall it.

Skip the "dielectric" grease. Think of what dielectric means (it means INSULATOR).. you don't want to add a layer of insulation to a contact. You want clean metal to metal contact.

[bimmer777]

I will take a more accurate reading on standing battery voltage, it could have been 12.6V but I just eyeballed it at 12V.

The output charge is STILL around 14.3-14.6V when the light goes on and stays there after more driving.

The rebuilt alternator came in a new box and looked brand new. I even thought it was brand new as there was not one single sign that it was ever on a car, even the mounting bracket did not have any scratches.

I did NOT clean the lead (singe positive one as the other side is a plastic clip) as it looked clean but I will do that today just to make sure.

I am also thinking on swapping out the voltage regulator from my old alternator. The fact that battery light goes on only after car heats up may suggest that the regulator on the new alternator is faulty. Otherwise, I am at a loss for ideas here. Will report back with results.

[deilenberger]

Originally Posted by bimmer777

I will take a more accurate reading on standing battery voltage, it could have been 12.6V but I just eyeballed it at 12V.

The output charge is STILL around 14.3-14.6V when the light goes on and stays there after more driving.

Where are you measuring this? And how long had the light been on (surface charge can be deceiving..)

The rebuilt alternator came in a new box and looked brand new. I even thought it was brand new as there was not one single sign that it was ever on a car, even the mounting bracket did not have any scratches.

Yup. Sounds like Bosch "rebuilt" - My WAG is they sell brand new ones as "rebuilt" to avoid conflict of interest with BMW selling the same thing for a whole bunch more money.

I did NOT clean the lead (singe positive one as the other side is a plastic clip) as it looked clean but I will do that today just to make sure.

This is the first thing to do.. since the behavior changed between your old alternator and the new alternator - then it's something to do with the replacement. Either bad contact somewhere or a bad alternator.

I am also thinking on swapping out the voltage regulator from my old alternator. The fact that battery light goes on only after car heats up may suggest that the regulator on the new alternator is faulty. Otherwise, I am at a loss for ideas here. Will report back with results.

It might - but in that case you're going to want a new alternator under the warranty anyway.. but at least it would narrow it down to the alternator. It wouldn't surprise me if your old regulator has worn brushes - so that's something to watch for, make sure they have some tension against the slip rings when installed.

[bimmer777]

UPDATE - After I posted on the forum and got the responses, I got in my car to drive to the garage to do clean the leads and possibly swap out the regulator. The car warmed up to full operating temperature and no battery light. I decided to take an extended test drive, push the car a little with AC full blast, radio on, lights on, and still no battery light. I decided to not do anything to it and parked it overnight. Next day (yesterday) drove out to the beach and no battery light.

I have only one possible explanation for this. I changed the new alternator first and test drove the car when the battery light showed up. Couple of days later, I swapped out the battery. When I swapped out the battery, the car was already hot and the battery light was ON. After I swapped battery, light still stayed on and thats when I went on the forum to post. Overnight something "reset" and all was well the next day. This is the best I could come up with although it doesn't make much sense as everything should have "reset" when I swapped the batteries. My only other guess would be the alternator being "broken in" but I don't know enough about them to make that assessment.

Thank you for all the help.