Standard industry belt diagnostics call for replacement of a serpentine belt if it shows three cracks in a three inch section. This is a good rule of thumb for Neoprene, but not so good for EPDM. EPDM belts inherently resist cracking because of the increased elasticity, so a visual check for cracks is not a very good indicator of true belt wear especially since they can run 100,000 miles or beyond with no visual cracks. A far better indicator of wear on EPDM belts is material loss.
Serpentine belt drives are exposed to grit, rocks, salt and water. Over time, these contaminants along with slight misalignments result in wear of the rubber rib surface. Like tires running on a highway, serpentine belts gradually lose material over time which results in failure modes defined by changes in belt profile. One problem associated with material loss is how the belt fits around the pulley. Belts are designed to allow clearance between itself and the pulley. When material loss occurs, the clearance is lost; thus, eliminating a way for water and debris to be passed through the system. This can result in belt hydroplaning.
• Over time, belt ribs lose material
• With material loss the space between the ribs increases
• The belt can “bottom out” on the pulley
• This causes belt slip and accelerated wear
• When water cannot channel out between the belt and pulley, hydroplaning (like a tire on a wet road) can result
• A persistent check engine light, reduced engine cooling, inconsistent power steering performance or poor A/C system performance are all signs of belt slip caused by wear.
The slightest material loss in belts means more to a car's drivability than you might think. Changing a belt during other component replacement is imperative. The best practice is to begin checking belts at 50,000 miles to ensure that the belt rib is uncompromised and is not showing wear. Remember, as little as 5% rib material loss can create issues.
• Turn engine off
• Insert tip of finger into the hole in gauge
• Reach under a straight section of belt and insert pin into a belt valley
• Use another finger to feel depth of gauge in belt