I'm planning to test that theory out. The trick is there is a large plastic cup to direct the cooling air covering the entire back side of the alternator, also the slip rings are nestled in quite tightly So I'm not sure how much you can see until the VR is actually removed

https://uploads.tapatalk-cdn.com/201...244fdeee09.jpg

Although this angle is not bad. Before I put the alternator back in I may remove three cover around there slip rings and glue in a clear window into the air duct.

- That air duct is useless, I removed mine.
- I think you miss my point: in most alternators, you can easily inspect by removing the VR in situ, this process (removal of VR) takes only 5-10 min.

Nope didn't miss point. I was considering removal of the VR only for repair. But: I needed to turn the slip rings which probably was much easier on the bench though running the engine would turn the alternator for me.

With a flex screw driver extension I believe you could remove the air duct cup and VR brush cover in place to get a good view and I plan to do that in a year or so to see if I can see wear on the inside v outside slip ring now that the polarity is reversed.

I did also invent a method to swap the polarity without removing or replacing the brushes. If caught early enough you could nearly double the lifespan of your alternator, probably 70% longer and that should get you 25-30 years on an X5, likely "lifetime".

AWR-fix: Valeo Alternaror Refurbish
 

I doubt you can say that with any degree of certainty. Have you ever measured the temp on your bridge rectifier pack after you started the car with a dead battery and it spends 5-10 minutes outputting 60-80A?

The fins are sideways in back of the alternator and will not get any kind of decent air flow through them without the air cap. Nothing worse than heat on the diode.

I've built circuits that put so much heat thru the drive FET that they literally desoldered themselves (more amazingly without destroying the FET), I would definitely not add more heat shock to the diodes they aren't Incorporated into the VR so much more difficult to replace.