Another Problem With Belt Tensioner
 

I have an 89 300TE, had to have an alternator replaced 4 months ago in the middle of Oklahoma, the shop got the alternator from an Advance Auto, and the other day it failed, I have since replaced the alternator with a Bosch, taking the old off and putting the new on I did not have to use the tensioner, I was able to get the belt off and on without using it. Is my tensioner ready for replacement? Do I have to take the fan and shroud off to replace the tensioner?? Do I need a special tool for the fan?? Could a bad tensioner cause an alternator to go bad in 12000 miles??

Thanks for all your help

Is your belt tension correct? That would be the first question to answer when determining if the tensioner is bad. Removing the alternator the way you did does not really say anything bad about the tensioner.

While a TIGHT belt might ruin the bearings in an alternator... No, belt tension would not make the alternator go bad in four months.

Did you really drive 12,000 miles in four months?

You can remove the fan from the clutch with an ordinary metric hex key.

The shroud is easy to remove.

Belt tensioner
 

Yes I drive on average 3000 miles a month, I use the wagon to haul my samples. My last Benz was a 97 C230, Bought it in 99 with 19000 miles and it was totaled this year and had 240000 miles on it.
Thanks for the info on the fan and shroud I will check the tensioner this weekend.

one thing that you may have overlooked is that a loose belt will not drive the alternator fast enough to provide enough power.

tensioner
 

If the belt wasnt driving the alternator fast enough would that be enough to cause premature failure of the alternator??

How did your AC work this past summer? Did you have any trouble with the compressor disengaging and causing the AC to stop cooling?

If not, your belt is not loose enough to not spin the alternator at the proper speed. The compressor has a speed sensor that will cause it to disengage if the belt slips. It takes a lot more power to run the AC compressor than the alternator, so if the belt is not slipping on the compressor, certainly it is not slipping on the alternator.

Go pull on your belt. Does it seem loose to you? How far can you move it?

AC worked fine all summer, and when I pull on the belt it seems to be tight.