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Spray bottle test

By Steve Schaeber, MACS Technical Editor

Replacing the accessory drive belt is one of those things that usually falls under the periodic maintenance category, and is something that technicians learn how to do when they first start working on vehicles. These belts are also commonly replaced due to noise issues, which are often difficult to diagnose.

This noise is something we’ve all heard before; that squeak-y, squeak-y, squeak-y sound coming from the drive belt while the engine is running. Sometimes it may go away after driving for a few minutes, but sometimes it will not stop, eventually annoying the driver enough to do something about it. All too often, technicians will replace the belt, thinking it’s worn out and no longer able to grip against the pulleys. This may temporarily solve the problem, but it’s likely to return if the root cause is not addressed.

Belt noises are not usually caused by problems with the belt itself, but rather are attributable to either alignment or tension issues in the Accessory Belt Drive System (ABDS). Knowing what particular type of noise it is can help pinpoint the cause.

Belt noises are not usually caused by problems with the belt itself…

Belt noises are not usually caused by problems with the belt itself…

A chirping noise usually indicates misalignment between pulleys and idlers. Possibilities can be item wear, pulley damage or improper component mounting.

If a belt is squealing however, it’s usually due to a loss of tension in the system, caused by a worn out belt, a failing tensioner, or both. To return the system to “like new” condition, both the belt and tensioner must be replaced together.

Check out the GatesAutoTraining channel on YouTube for a video called Gates Spray Bottle Test. It’s a neat, simple way to help pinpoint the cause of belt noise. More detail is in the video, but here’s basically how it works:

  • If spraying the belt with water makes the noise get louder, it’s usually due to a tension problem indicating both the belt and tensioner should be replaced.
  • If the noise goes away temporarily and then comes back, this indicates one or more pulleys are misaligned.

Note: While you’re on YouTube, be sure to check out the MACSWorldwide channel. Send an e-mail to and let me know which video is your favorite!

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