serpentine engine belt

Does anyone know the average life of the engine serpentine drive belt?

When you start to see cracks or missing segments on the cogs.

To be honest, I've never seen an S-belt itself fail. In my experience, failure always occured from a bad belt driven accessory. A pulley bearing locks up and burns up the belt, or a pulley gets wobbly, goes out of plane and causes the belt to pop off or break. If everything looks/sounds/feels good, I let it go until an idler or tensioner starts making noise, then replace those along with a new belt. FWIW, my 2001 windstar still has the factory S-belt (and all the pullies) at 75Kmi. Factory battery too! :uhoh: I'm done for.:banghead:

Joel