Replacing tensioner pulley - question about damage

[AngeloSRQ]

Hi I'm a recent new owner of a 2002 525i Touring with 221000 miles. The main accessory drive belt/serpentine belt broke on the highway yesterday. I didn't have any squealing from the belt before so it was quite a surprise. Without removing the fan shroud or anything I could see the main tensioner pulley was sort of shredded, all sorts of bits of it broken off.

I figured the belt broke just because it was old and worn out (from looking at the removed damaged belt) but I'm not sure if the belt snapping broke the pulley or the pulley some how blew up (which came first, chicken or egg) causing the belt to snap. I'm looking to do this all myself and am hopeful that just replacing the belts and tensioner pulley will fix it, unless someone can tell me if this is indicative of a more serious issue. The were no problems with engine temperature, the alternator or power steering before the belt broke.

[geargrinder]

I've not ever heard of tensioner pulleys 'shredding' myself.

Pix would be good.

Take the pulley off and inspect the bearings and how smooth it rolls.

I'd be pretty sure SOMETHING seized up first and that shredded the belt, maybe the tensioner started to seize while the belt slipped over it until it heated it up and took out a few ribs and parts which then shredded the belt (all that may have happened in span of 3-5 seconds).

You'll want to inspect all the other pulleys and accessories and be sure they are turning smoothly and nothing else was damaged by the thrashing belt. Nobody can tell you over the internet if something else is bad too, but I'd be trying to triple confirm it wasn't something else that seized first.

[jicaino]

Common issue on the eccentric idler pulley arrangement of those cars. The pulley seizes and melts at contact with the spinning belt and it blows up. If you can, replace the hidraulic tensioner with the mechanic INA assembly https://www.eeuroparts.com/Parts/101...l-11281427252/ and this belt: https://www.eeuroparts.com/Parts/400...5-11281469266/
Way more reliable and cheap