1992 318i. Alternator replaced in Aug, then had to be replaced again in Oct, and again in Dec. Seems to work for about 800 miles then goes again. What could be causing this damage to new alternators?

Your alternator could have bad wiring to it.

Check this out....
http://www.autoshop101.com/trainmodules/alternator/alt102.html

A friend had a repeat bad alternator and he stated that once he replaced the alternator for the 2nd time, he measured the voltage at all the wires coming into alternator and the voltage was reading low for the sense line. The voltage going to the batter was way too high. He ended up replacing some of the wiring and the problem went away.

Keep in mind this is just an isolated incident, so your problem can obviously be different.

Lots of cheeper alternators are remans, so some of them are only partly rebuilt, get a new alt. Later Mark.

check the ground wire from the motor to the body of the car.. also make sure when you put the next one on that you don't put to much presure on the belt... to much presure will burn it right out..