The serpentine belts do tend to last a long time. I think its because the ribs running on most of the pulleys add a lot more grip then the one single groove of a V belt, so the flat belt doesn't as allow much slipping like the V belt design. does. The less slipping, the less heat, and the longer life span. I think the reason most people change the serpentine belt is because of the cracks they see between the cogs across the belts. Most damaged serpentine belts I've seen were split along its length when the belt got off the sides of the pulleys. Gene