- 1983 BMW 735i (E23), alternator went out at 15y/115K time.
- My current 1998 528i with 170K, the alternator is still stock.

There are basically 3 modes of failure for most people with 50-50 city-highway driving (100% highway driving is better):

1. The bearings (especially the front bearing b/c it handles the load from the serpentine belt) usually go out at 160K-240K range, who knows...

2. The brushes/slip rings wear out at 180K or so. Bimmerfest has a whole bunch of photos of rebuild.

3. Voltage Regulator, this part can go out any time, anywhere from 30K (rare) to 240K. This part is completely unpredictable.

I used to do rebuild simply b/c the re-mfg alternators from local parts stores are no good. The rebuild includes: new bearings, brushes, slip rings and VR.

Lately, Bosch releases a BRAND-NEW alternator for M52, M4 engines...about $200 or so. The Bosch PN is AL0703N (the "N" stands for new, stay away from "X", which is rebuilt).

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT