Serpentine Belt Replacement

When you replace a serpentine belt for your customer, are you only providing half of the service?

When to change the serpentine belt depends on a few things but, generally speaking, for optimal performance the serpentine belt will have to be changed more often than its “V” predecessors. In terms of time and mileage, this would generally translate to between 50,000 and 60,000 miles, or approximately four years. Under-hood heat, accessory load, the quantity of accessories, and exposure to road debris all affect the longevity of the belt. Until recently, most belts were constructed of Neoprene material. Today, most serpentine belts feature 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. EPDM belts rarely show symptoms of wear, even at very high mileage.

As EPDM belts age, they gradually lose rubber material — similar to the way 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.

Belt wear after 100,000 miles

EPDM: Signs of Wear 

The diagram below shows how EPDM belts wear as they age. Although the ribs have not become shorter, material has been lost in the valleys of the ribs (indicated in red), making the space between ribs wider. As more material is lost, the pulleys ride deeper into the belt valleys resulting in slip, noise and hydroplaning.


Obvious Signs of Wear 

Although EPDM belts do not tend to crack with age, they can still exhibit other symptoms that are caused by problems with the accessory drive — such as tensioner misalignment or failure, pulley misalignment, excessive heat, or bearing failure in one of the other components. If the belt exhibits one or more of these symptoms, it needs to be replaced. If it fails, it could damage other system components in addition to stranding your customer. Many warranty-claim failures on alternators and other parts are actually caused by worn or improperly adjusted serpentine belts.

When a serpentine belt wears out, several problems can occur that reduce performance of the Accessory Belt Drive System. 

BELT SLIP — LOSS OF TRACTION Like a tire, a worn belt can lose traction (slip) on the pulleys, particularly in high-load and/or wet conditions. Slip can cause belt/pulley temperatures to rise by up to 50% — leading to early accessory bearing failure.

HYDROPLANING This occurs when water cannot be effectively channeled away between a worn belt and the pulleys. The belt then “hydroplanes” on a film of water, resulting in loss of power transmission to the accessories. This can often result in the “Check Engine” or “Alternator Charging” warning lights to come on.

ELONGATION Material loss can also 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, also lowering accessory performance.

MISALIGNMENT Misalignment wear can also be an indication that the internal components of the tensioner have failed. Material loss and subsequent changes to effective length on belts can also cause belt slip, resulting in noise, vibration and high heat, which can damage accessory bearings and cause accessories to

With sufficient material loss, the pulley ribs “bottom out” in the valleys and ride on the belt cord. This reduces the surface contact on the valley sides, where the traction is generated. Wear also increases the effective belt length, lowering the tension in the system, which also reduces traction.

When inspecting the serpentine belt, if it appears to be glazed (shiny), show cuts, cracks or other deterioration on either side or on the edges, has chunks missing from it, or is merely noisy — it has to be changed. It's helpful if you can determine the cause of a particular problem — from normal wear to damage — so you can be assured that the replacement belt will last the full duration of its service life.

What about the serpentine belt tensioner or idler pulley? 

Once the determination has been made to replace the belt, you need to go one step further.

Remember if the serpentine belt has 60,000 to 100,000 miles on it, so does the belt tensioner or idler pulley. It is the perfect time to replace them. If that part fails shortly after you sell the belt replacement, the belt could be damaged or destroyed and you very well could have an irate customer and possible warranty claim. You could end up doing the job again, and there is definitely no profit in that!

Replacing a serpentine belt tensioner is usually an easy project. The one factor that can make it difficult is how the engine is mounted. On front wheel drive cars, where the engine is mounted transversely, it can be difficult to access the belt tensioner. Most however, are simple and straight forward.

By changing the tensioner or idler pulley when you replace the serpentine belt, you are insuring that the job is being done right, you have a satisfied customer, and at the same time, you add a little more profit to the bottom line.


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