Well, I have but only one thing to say to your mechanics....Of coarse it is "something electrical".....DUH!!!

The leading cause of premature alternator death is a shorted or sulfated battery (which you say has been replaced), and high resistance in the charging system circuits.

Here is what needs to be done:

• The battery needs to be thoroughly tested to make sure that it is in good working condition, fully charged, and does not have excessively high impedance. I know you said it is new, but "NEW" and "GOOD" are NOT the same thing. It needs to be tested to verify that it is good.
• Then voltage drop tests should be performed on ALL of the charging system circuits. High voltage drop on either of the battery circuits to the alternator can "trick" the alternator's internal regulator (IC unit) into thinking that the battery is discharged, even if it is not. If this happens, the regulator will keep the alternator at peak output when it is not needed and burn the thing up.
• A large voltage drop on the negative battery cable can also cause this. It is very important to check the ENTIRE system. Otherwise you will probably end up buying alternator #6.

I am providing a couple links here to help you. One is the wiring diagram for your charging system. The other is a basic instruction published by a company named FLUKE that explains how voltage drop tests should be performed.

G20-Charging-system.gif

VoltageDropFuke.pdf

I thought I might also add that the most common place for high charging system circuit resistance is loose or corroded battery cable ends. The second most likely place to find a problem would be in the fuse box. Sometimes the fuses, (100 Amp and 7.5 Amp, shown in the wiring diagram) will get hot due to loose connections in the fuse block. I have replaced many fuse block connector terminals due to this.

Hi again,

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-Autotech58