yeah I agree with others here those accessory drive belts only have limited operating life ,even the timing belts are recommended to be changed every 60,000 miles to keep your vehicle running @ peak efficiency,and the serpentine would be less im not sure but I believe it is somewhere around 30-40,000 but I might be incorrect if someone has a manual to post the recommended amount of mileage to replace that belt please do, another thing to do twhen you replace it is check every so often when your under hood to keep track of the condition of the belt and if the belt is getting alot of cracks in it change it again the problem is the life of the belt depends on alot of things like driving habits ,traffic conditions, weather conditions ,length of driving times ,operating condition of all the accesories the belts run they all have an influence on the life expectancy of the belt ,one thing you can do too is keep a journal on your vehicle on things like fuel ups write down how much fuel and what mileage and date ,the mileage and date of your oil changes and other maintenance items like tires (write the make and model down and which ones were replaced)light bulbs(which ones and make),and topping of fluids(how much and how often) you get the picture good luck and drive safe