Belt Wear & Why Your Auto Mechanic Isn’t Crazy

Just because your serpentine belt doesn’t appear to be cracked, don’t think your auto mechanic is wrong when he says it needs to be replaced. Drive belt technology has improved in newer vehicles, meaning there is new criteria for determining if a belt is worn. If you have a late-model vehicle, listen up.


Let’s start with a quick lesson on drive belts, so we’re all on the same page. Drive belts come in two forms, or types: v-belts and serpentine belts. Timing belts, however, are different. A timing belt makes the engine work. Vehicles have 1 timing belt and anywhere from 1 to 4 drive-belts. Drive belts transfer power from the engine to your vehicle’s A/C, power steering, and alternator. Without drive belts, these systems don’t operate. Common knowledge tells us that drive belts need to be replaced when they show signs of cracking. This is true. However, in newer vehicles, a drive belt that has naturally reached the end of its life will not show signs of cracking.

Like the water-proof iPhone, technology has enhanced the quality of automotive drive belts. Ah, technology. Drive-belts in late-model vehicles last longer, and recommended service intervals are also longer. The rules for what determines if a belt is worn have changed, as well. These belts no longer show the classic sign of wear: cracks. Instead, what determines if the belt is worn and needs to be replaced is the depth of the belt’s grooves. When the grooves are too shallow, the belt is no longer able to grip the pulley, making it slip. When this happens, it creates noise (oftentimes a squeal) and puts strain on the vehicle’s A/C, power steering, and/or alternator system and can lead to those systems failing–bummer!


Both of these belts are worn. The left is from an older vehicle and the right is from a late-model vehicle (the depth of the grooves were measured to determine it needed to be replaced).

To prevent system failures, periodically the belts need to be replaced. But instead of merely looking at the drive belt(s) to determine if they need to be replaced, your auto mechanic will measure the depth of the belt’s grooves (similar to what is done when measuring the tread depth of tires). Your auto mechanic can tell if the belt needs to be replaced when the grooves on the belt (see image) are worn down. If the drive belt grooves are below the manufacturer’s recommended depth, the belt needs to be changed. Your auto mechanic will then recommend that your belt is due for replacement.

The good news to you? These new and improved belts can last up to 100,000 miles. This is if all the related parts (pulleys, tensioners, etc.) are maintained in working order and don’t cause the belt abnormal wear.

This is important to know because if your auto mechanic tells you the belt needs to be replaced, and it looks perfectly fine to you, just know, it’s probably not.

As part of Community Auto’s procedure, we save your broken parts for your viewing after the repair. And if you’re interested, we even provide a lesson on the part failure and related systems. This is because we feel it is our job to educate you on how your vehicle works. Since who has time for learning that on their own?

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