Starting in 2000, some carmakers began installing a new kind of serpentine belt made of ethylene propylene diene monomer (EPDM). The new belts last much longer and handle the heat better than the older neoprene formulations. That means fewer belt changes over the life of your vehicle. In fact, EPDM can go almost 100,000 miles between changes! But since EPDM doesn't crack like the old neoprene belts, you can't do a visual check. The only way to gauge belt wear is with—you guessed it—a belt gauge (photo). DIYers can get a free belt wear gauge at www.gatesbeltwear.com.
If it's time to chuck your EPDM belt, replace it with the same kind. Don't be fooled by low-price belts. They're usually made from neoprene. Also, if your car has a neoprene belt and it's cracked, consider replacing it with EPDM. Yes, it's that much better.