[fluidkaos]

What might cause alternators to keep failing repeatedly?

I've had the car since new in 2010 and replaced the alternator for the first time in 2021 after it left me stranded on the side of the road. There's nothing unusual about that; the car was over a decade old and things go bad. The problem is that since then I've had my alternator fail every year. I replaced it again in 2022, and have another on order to replace the one failing me now. I've been ordering the remanufactured Bosch units from FCP. Thankfully the lifetime warranty covered everything but shipping for all but the first one.

I don't have any modifications that cause significant electrical load (like aftermarket sound systems, etc.) The only mods that tie into power in any significant way are my JB4 and meth kit. I did have an electrical gremlin pop up in one of the sensors connected to the FRM a while back, but that's been fixed since the first alternator replacement.

The chassis ground and alternator frame ground Ohm out good with a multimeter, so it's not likely a grounding issue.

Could this just be the price I pay for "free" remanufactured alternators, or might there be an underlying issue causing the failures?

[zou_n@hotmail.com]

Hi, does the bad alternator cause e90 crank but no start? Thanks

[e90yyc]

Reman or not, that definitely does not sound normal. Bosch reman alternator should be just as good as a new one. The wear items—bearing at front and rear of shaft, and the voltage regulator (brushes)—are replaced. Not sure about the rectifier/diode bridge, as I believe this is soldered to the alternator housing, and isn’t *typically* something that fails.

All in all, I don’t think alternators are a very common failure item in these cars. Yes, the voltage regulator can go, but that’s a cheap and easy replacement.

Any idea how it’s failing? Have you done any checking/post-mortem testing?

How old is your battery?

I don’t think you’re just repeatedly getting bad alternators. Is there anything noteworthy about your car in terms of electrical loads? Aftermarket amplifier/subs/etc?

And just to confirm, what’s the part number of the unit you’ve installed, and what is the last 7 digits of your VIN? Are you certain you installed the same amperage alternator that you removed? Not sure if there’s more than one option for 335 but I’m pretty sure for 328 there was a 150 and 180 amp.

[fluidkaos]

The diodes failed on my first alternator after 11 years of faithful duty. I don't remember what caused the second one to fail.

This one I've not fully diagnosed, just saw signs of failure and placed an order for the replacement before I got stranded again. It's only putting out 13.5V instead of the normal 14.2V, it's boiling hot, and noisy. I haven't checked any further than that yet.

My battery is about a year old. I've been changing them out every 4-5 years as needed.

I don't have any modifications that cause significant electrical load (like aftermarket sound systems, etc.) The only mods that tie into power in any significant way are my JB4, meth kit, and dash cam.

Definitely using the 180A alternator as it's the only option for the 335i.