Why is it that some people's alternators last for 200k miles whereas some others last for only 100k? What causes wear on the alternator and what can you do to try to prolong its life?

 

The power load (or how much electrical power you need) will affect the life of the alt. If your needs of load are high ( amp. & lights etc.) = alt life is going to be shorter.
Hope this helped.

 

just to add, two more things other than amperage load on the alternator that would advance wear is driving style. If an alternator spends more time at 6k than idle, then obviously it will wear more. the other would be climate, obviously lots of cold starts are going to be bad on electrical components) fyi, i just replaced the original alternator on my 89 dx hatch at 242,000 (work commute car)

 

Thanks for the replies! It all makes a lot of sense.

 

sometimes- people will install some junk aftermarket alternator (pep boys, auto zone, napa, etc..) and they will last all of one week sometimes less. I replaced my 150,000 mile alternator simply beacause the bearing was squeaking when cold. If you are replacing yours, I highly recommend a Honda/Acura piece- pricey but reliable.