How to Tell if Your Drive Belt or Fan Belt Is Bad

Mia Bevacqua
April 5, 2018

Signs of a failing drive belt

A faulty drive belt can cause a number of problems. These are some of the most common.

1. You hear a squealing noise: A drive belt that is stretched or out of adjustment can make a squealing noise. The noise is caused by the belt slipping on the pulleys, insufficiently driving them. This is usually most noticeable when the vehicle is first started in the morning, as the drive belt has not yet heated up and become pliable.

2. You see physical damage: A belt that is visibly cracked, frayed, torn or broken is no good. You’ll need a new one.

3. Warning lights are on: The alternator is driven by the drive belt. If the belt slips or breaks, the car’s charging system won’t have voltage. As a result, a cluster of warning lights may pop up on the dash. This is especially true on cars made in the last 10 or 20 years, which have dozens of voltage-dependent computers.

4. The battery goes dead: The battery is basically a storage device for electrical energy created by the alternator. If the drive belt slips or breaks, the alternator won’t properly charge the battery. As a result, the battery will die.

5. Lack of power steering: Vehicles with hydraulic power steering have a belt-driven pump. A loose or broken belt can result in a lack of steering assist.

6. Engine overheating: On many cars, the water pump is run by the drive belt. A broken or slipping belt can cause the water pump to stop turning, making the engine overheat. If this happens, pull off the road in a safe place and turn off the engine. Overheating can kill an engine quickly and cost you a lot of money.

Get it diagnosed by a professional

What is the drive belt?

The drive belt, sometimes called the fan belt, conveys power to a lot of important parts of your car. The alternatorpower steering pumpwater pump and air conditioning compressor are typically mounted on the front of your engine, and rely on the drive belt to operate. 

Each of these parts has a pulley attached, as does the engine crankshaft, and the drive belt wraps around these pulleys. When the engine is running, the crankshaft pulley turns, moving the drive belt, which then turns the accessory pulleys. 

There are two basic types of drive belts: V-belts and serpentine belts.


These belts get their name from their shape, which tapers from wide to narrow, forming a “V.” Usually, V-belts are found on older vehicles, produced at least a couple of decades ago. In the beginning, only one V-belt — known as a fan belt — was used to drive all of the engine accessories.

As cars became more complex, automakers started adding more accessories to the engine. To compensate, they began using multiple V-belts. Each belt drove one or two of the accessories. For example, one may drive the power steering and alternator, while another drives the water pump.

Some V-belts are relatively smooth on both sides, while others have multiple small grooves on the pulley side. Generally, multi-groove “ribbed” V-belts are more flexible and build up less heat. V-belts can be adjusted via an adjustment pulley, or pivot and adjustment bolts. 

Serpentine belt

The serpentine belt is basically just a longer belt that “snakes” around all the engine accessories. It may have grooves on one side or both. Typically, serpentine belts last longer and transmit power more efficiently than V-belts.

Unlike V-belts, serpentine belts aren’t adjustable. Instead, an automatic tensioner is used to keep the belt taut. 

» MORE: What happens if a serpentine belt breaks?

How to fix the problem

Sometimes a V-belt can be adjusted to restore performance. On vehicles with a serpentine belt, replacing the tensioner may cure the issue. 

Regardless of type, if the drive belt is damaged, worn or broken, it should be replaced. On some cars, especially vintage ones, this is an easy task for most people to tackle. But cars made in the last 30 years have belts that snake all over. Replacing these belts may even require the use of special tools. In such cases, drive belt replacement is typically best left to a qualified professional.

A technician will visually inspect the serpentine belt for wear or fluid contamination. The belt’s grooves will be checked for cracking or breakage. On vehicles equipped with automatic belt tensioner, there’s usually a gauge on the tensioner that indicates how much the belt has stretched — this will also be checked.

To replace a serpentine belt, the technician will loosen the tensioner, remove the old belt, route the new one over the accessories, and then release the tensioner so that it puts tension on the belt. The vehicle will then be started to check that the belt has been properly routed.

It’s also important to inspect the accessory pulleys when replacing a drive belt of any kind. Worn or stuck pulleys can damage a new belt in short order.


Mia Bevacqua

About the Author

Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.

1 User Comment

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By , January 22, 2019
Thank you, this article was very helpful

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