The new serpentine belts that are constructed of EPDM construction, which stands for ethylene propylene diene M-class rubber. Visually, it’s hard to tell the two types of belts apart, but EPDM belts far outlast and outperform any of their predecessors. Older belts last 50-60 K but I have seen them go a lot farther if they stay clean. The newer EPDM belts will go a 100K easily. The problem is they will not show cracking and materials lose as the older belts do. The valley of the belts wears out making the use of a gauge mandatory to check a belt. They will then begin to make noise and slip the good news is they are very quiet otherwise, even when starting in cold weather with the AC on which has been a problem for years. When the valley wears the length of the belt also will increase causing problems.A gates wear gauge can be obtained at this site.[url”>http://www.gatesprograms.com/beltwear