You aren't warming it, you are cooling it. The alternator is a heat generator (when it is charging...), it isn't passive.

See the attached presentation, some more info on the Bosch water cooled alternators, and some heat transfer figures.

http://www.waiglobal.com/images/Publ...1112%20(2).pdf

Be interesting to know what the failure mode was on yours.

I read the document and see it is rated to 180c which is more than 4x the temperature here right now (41c) but the water temp is at least 70c all the time while air temp under the hood is rarely over 60c.

Why add heat. I have never heard a functional alternator so I really don't get all the harping on low dba.

Bottom line new rebuilt Bosch unit is out for delivery & will go in tomorrow. I just don't get outside places that are cold how this got off the ground.

Additionally, if it's so good why did BMW go away from it?

According to the attachment it is the windings that are rated to 180C. They are cooled directly by the coolant, so that seems logical.

Later in the attachment, there is information about the failure mode relating to the diodes. The rectifier consists of diodes that convert the AC current to DC, in order to charge the battery. The diodes are a one way electrical check valve, with no resistance in one direction, and very high/infinite resistance in the other direction. So they produce a lot of heat, by design. That is the heat source that the coolant is dealing with, indirectly. If you want to have high current for fast charging at low engine speeds, (required due to lots of hungry accessories, and made worse by fuel-efficient shift programs) you end up with lower air flow and thus alternator failures. Or the designer could spec a lower performance alternator, and then you get flat batteries.

Once you think of the alternator as a heat source (like the engine block) then cooling it most efficiently becomes a logical goal. You are not warming the alternator, that is the misunderstanding. I suppose you could warm the alternator, but you would need hot coolant, and a cold alternator, and I don't know what situation would produce that. The alternator warms up faster than the engine, so it provides heat, it doesn't absorb it, after a cold start.

Why did they move away from it? I have no idea. I am glad they did though. Less to break. That is why I personally would have searched out design alternatives, to reduce eventual repair costs.

The alternator was designed to handle engine coolant temperature for a specified life cycle. The constant temperature is part of the lifecycle calculation, verified by testing. It doesn't matter if a non coolant alternator would be better, the alternator as designed met what BMW felt was the necessary specifications for performance and reliability and cost.

Designs are changed for a variety of reasons. Assuming there is not an excess of failures prior to the lifecycle goal of a part, changes are most often cost reductions or advances in technology First run products either by the manufacturer and/or the customer are tested to verify they meet the design criteria as are random parts in each production run. Even if the strictest of procedures are followed there can be excess failures but I don't think that is the case with the original equipment alternator.

Fair enough. I will ask the vendor to let me know what the point of failure was. I won't be holding my breath awaiting that input.

Alternator came. Biggest oddest looking alternator I have ever seen.

http://i20.photobucket.com/albums/b2...ps025430b8.jpg

http://i20.photobucket.com/albums/b2...ps680e7b9c.jpg

Whole darn thing is sealed up!

http://i20.photobucket.com/albums/b2...ps7c6df86e.jpg
Rear O ring.

http://i20.photobucket.com/albums/b2...psec716d8b.jpg

Alternator is in.

Is it normal for the car display to read a volt low?

Both with the bad alternator and new my Fluke reads a full volt higher.

What is the range test 9 reads on the OBC while driving with the new alternator?

That is the volt low I was talking about.

The fluke reads 14.2 - 14.9 running. (not moving)

Test 9 reads 13.2- 13.9.

On the drive to the mechanic, after trickling for 2 days before I started it the fluke read 14.7, test 9 13.5.

After I started it, fluke 13.8, test 9 12.3.

It got down to 11.3 on the 12 mile drive but ran fine and started normally with normal crank speed.

The battery light is off and hopefully that is the end of electrical issues.

If test 9 reads between 13-14 volts I think its perfectly fine, that should indicate a healthy alternator (at least that's what I have read)

Your fluke might be off a volt, test 9 seems to be pretty accurate from what I read. Hope your electrical issues are over!