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How to Diagnose Serpentine Belt Noise: 3 Easy Tips

A belt tensioner, which, when loose, can lead to serpentine belt noise.

Serpentine belt noise is one of the most annoying sounds your engine will ever make. The embarrassment of driving around with a squealing motor that only seems to get louder when you hit the gas is overshadowed, however, by anxiety about whether you might be looking at an extensive repair. Fortunately, most belt noise is relatively benign, but that doesn’t mean you can ignore it.

Check out these three tips for dealing with a noisy belt before it becomes a bigger problem.

1. Look for a Dry or Cracked Belt

Over time, noise can often originate from a belt that has started to dry out due to age, the friction of being constantly in motion and heat from the engine itself. As this process continues, the belt is no longer able to maintain the tension required to properly grip the pulleys that it links together, and it starts to slip — producing the noise. If your belt is showing any cracks, that’s a strong indication that it’s dried to the point where it’s at risk of snapping, which means it’s time to replace it.

2. Check to Make Sure Coolant Isn’t Leaking

Another common cause of serpentine belt noise is exposure to coolant. If you recently added antifreeze to your radiator and spilled some on your belt, it can quickly cause a squealing sound. The same is true if any part of your cooling system is leaking, as the engine fan can blow small amounts of coolant back onto the belt itself. Unfortunately, it’s not easy to clean antifreeze from a rubber belt once it’s sunk in, although some belt dressing products claim to quiet down the sound. You may be looking at a replacement to get the noise to go away.

3. Tighten the Idler Pulley

A loose belt that’s slipping will squeal. If your belt looks to be in good shape and isn’t dried out, then it’s a good idea to check the tension on the idler pulley to make sure it’s strong enough to take all the slack out of the belt as it spins. You can purchase a specific serpentine belt tool to tighten your idler pulley. It’s a simple job you can do with the belt still attached to the engine.

A loud belt might be an annoyance, but a snapped belt could leave you stranded. Don’t ignore what your engine is trying to tell you, and make sure to investigate why your belt is making noise as soon as you can.

Check out all the belts and hoses available on NAPA Online or trust one of our 17,000 NAPA Auto Care locations for routine maintenance and repairs. For more information on serpentine belt noise, chat with a knowledgeable expert at your local NAPA Auto Parts store.

Photo courtesy of Wikimedia Commons.

Benjamin Hunting View All

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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