Belt Wear Battle: Chloroprene vs. EPDM

Since the late 1990s, automotive manufacturers have phased out Chloroprene (neoprene) serpentine belts and are now installing ethylene propylene diene monomer (EPDM for short) belts on current vehicle models.

While it's hard to tell Chloroprene and EPDM belts apart visually, EPDM belts far outlast and outperform their predecessors. Chloroprene belts have a life expectancy of 50-60K miles and as they wear out, cracks, chunk-outs, and other visual signs of wear will occur. EPDM belts rarely show these symptoms, even at 90K+ miles. Instead, as EPDM belts age they gradually lose rubber material similar to the way a vehicle’s tires wear out. Over a period of 100,000 miles, a belt can lose up to 10% of its rib material. While this may not seem like a lot, the consequences can be significant. Just 5% wear can begin to negatively impact vehicle performance.

Belt wear after 100,000 miles

Common Belt Wear Problems

When EPDM serpentine belts lose material on the sides of their ribs, the space between the ribs widens. With excessive material loss, the pulley sheaves “bottom out” in the valley of the serpentine belt and can potentially damage the belt cord. As the side of the rib wears, the wedging force is reduced, lowering the tension in the system and reducing its coefficient of friction. Wear also increases the effective belt length, lowering the tension in the system and reducing traction.

This potentially results in slip, noise, and hydroplaning. A slipping belt generates heat, causing premature failure of bearings and other system components. Heat changes the viscosity of the grease inside the bearings. As the grease thins, it leaks/purges out of bearing seals and causes problems. Heat can also put a strain on other components within an engine, causing them to malfunction and potentially fail (such as bearings, plastic pulleys and alternators).

Belt wear problems that reduce performance of the serpentine system include:
  • BELT SLIP: Like a tire, a worn belt can lose traction or slip on the pulleys, particularly in high-load or wet conditions. Belt slip can cause pulley temperatures to rise, leading to early accessory bearing failure. Material loss and subsequent changes to the effective length of belts can also cause belt slip, resulting in noise, vibration, and high heat.
  • HYDROPLANING: When water cannot be effectively channeled away between a worn belt and the pulleys, the belt can hydroplane on a film of water, resulting in loss of power transmission to the accessories. This can result in a vehicle’s "check engine" or “alternator charging” warning lights intermittently appearing on the dashboard.
  • ELONGATION: Material loss can cause a change in the effective length of the belt, which can move the tensioner beyond its take-up range. This will reduce overall system tension, making the system more susceptible to slip from cold/wet environmental conditions and engine dynamics (AC engagement, full throttle accelerations). Accessory performance will subsequently be lowered.
  • MISALIGNMENT: There are many accessories the belt is routed around and they all have different mounting methods. Rubber dampers and worn bearings can lead to a misaligned belt pulley. Automatic tensioners have components that wear, causing misalignment in the tensioner and pulley. Misalignment causes excessive belt wear and heat. In addition, misalignment may be an indication that the internal components of the tensioner have failed. Because there are so many accessories, there’s potential the pulleys will not be aligned properly.

Use the Gates belt wear gauge to help you determine if a serpentine belt has lost enough material to negatively affect performance and warrant replacement. Learn more by clicking here.

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