My fan belts keep breaking on my 92 3.0L MPV. The fan clutch turns freely. The pully on the Alternator spins freely. When I put on a new belt it will loosen up as if it's stretching. I will adjust the alternator in the slide down to tighten it up but it eventually loosens up again. I eventually run out of room on the slide as I have to keep moving the Alternator down to tighten the belt. what could cuase this? I make sure the belt is not too tight or too loose. No more than 1/2 in play total. Meaning 1/4 inch flex on the belt at the top and bottom in the middle between pullys.

 

Check for any kind of pulley misalignment/wobble. That can stretch out belts quickly.