The original equipment belts on late-model vehicles are made of synthetic rubber that is far more durable, heat-resistant and wear-resistant than older materials. This means serpentine belts may last up to 100,000 miles or more before they have to be replaced, but that doesn’t mean they will last forever or won’t age prematurely on some vehicles under certain conditions. If you have a vehicle in your shop for belt replacement, diagnose why the belt needs to be replaced. Wear on a single component is rare and more than likely a worn tensioner, idler or pulley will cause or contribute to excessive belt wear — not just age. Also, decoupler pulleys wear out, causing excessive noise and a no-charge condition.