I just replaced the belt tensioner for the accesory drive belt. I noticed the belt had been running slid over towards the engine one groove on the a/c pulley only. I would put it back to the proper positon and it would slide back upon startup. I replaced the tensioner and no more problems. The old tensioner is a little bowed in the arm. I wonder how that happened?

 

too much torque.. LOL

 

maybe some coolant sprayed over there when your overflow tank got overfilled itself and caused the belt to slide to one side and that caused it to bend.