If Your Car’s Belts Are Noisy, This Is What It Means

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A car engine belt that's squealing or chirping indicates a problem that needs to be fixed.

Many years ago, while I worked as an auto mechanic, a customer brought in their vehicle complaining about a noisy fan belt. This was when self-adjusting serpentine belts first came on the scene.

Back in those days, the quick fix was spraying it with belt dressing. Unfortunately for me, because the idler pulley mounting bolt was loose, the dressing caused the belt to lose its grip on the pulleys. It flew off, tearing up the crankshaft sensor.

The customer and service manager were not pleased. It was one of those “uh-oh” moments you never forget. And it’s why you should never ignore a noisy serpentine belt.

Although it isn’t the same as a check engine light, a noisy serpentine belt does indicate something’s wrong with the drive belt system. But the belt may not be the culprit.

A serpentine drive belt can make all kinds of odd noises. It can squeak, squeal, chirp and clunk, imitating a bad engine-driven accessory or engine bearing. These noises can fool even the most experienced mechanic and lead to an expensive misdiagnosis.

Squeals and chirps are definitely the two most common serpentine belt noises and usually result from different problems.

  • Chirping is a series of sharp pulsing sounds. As engine speed increases with acceleration, the chirp pitch and volume stay constant.
  • Belt squeal means a high-pitched shrieking that can increase in volume with engine speed, but the pitch stays the same.

Reasons for Belt Noise

Besides normal wear and tear, any defective component in a drive belt system can cause belt noise or premature wear. Oil, antifreeze or power steering fluid leaking onto a belt will quickly cause a serpentine to deteriorate. The leak must be repaired and the pulleys thoroughly cleaned before installing a new belt.

With an inexpensive serpentine belt tool, replacing a serpentine belt is a simple DIY repair.

Note: Never use spray belt lube or dressing to quiet a serpentine belt. Both will contaminate and ruin the belt.

Reasons for belt chirp

The number one cause is misaligned engine pulleys, not the belt itself. If chirping persists after replacing the serpentine belt, the most likely causes are worn or dirty pulleys and/or pulley bearings, improper belt installation, or a cut-rate or defective belt.

Here’s what to look for:

  • Use a straight edge or laser alignment tool to ensure pulley alignment is parallel.
  • Check that all mounting brackets, pulleys, tensioners and idler wheels are secured tightly to the engine.
  • Check that all accessory pulleys and idler wheels spin freely and smoothly without wobbling. Be sure they don’t show signs of excess wear, burrs, rust or flat spots.
  • Carefully inspect all component pulleys like air conditioning, power steering, alternator and harmonic balancer for wear or contamination from an old belt gunking up pulley grooves.

Reasons for belt squeal

According to Gates, one of the largest producers of drive belts in the world, low belt tension is the main reason for squealing belts.

A stretched or worn belt, fatigued spring-loaded automatic belt tensioner, manual belt tensioner out of adjustment, wrong belt or a belt installed incorrectly can all cause low belt tension. Unlike “V” belts of the past, serpentine belts wear on both sides.

Here’s what to look for:

  • Check that the tensioner swings freely without squeaking, binding, clicking or rattling from a weak, rusted or busted tensioner spring.
  • Check for worn belt ribs.
  • Check that the smooth/top side of belt and idler wheels aren’t shiny or glazed from overheating.
  • Check for contamination from oil, power steering fluid, antifreeze, belt dressing or pulley grooves mucked up from an old belt or damaged from stones or road debris.
  • Check for a poor quality belt or poor installation. And be sure it’s the right length.

How To Check for Belt Wear

Beginning around 2000, major vehicle manufacturers began installing serpentine belts made from ethylene propylene diene monomer (EPDM).

Unlike traditional Chloroprene (neoprene) engine drive/accessory belts, EPDM belts can last between 50,000 and 100,000 miles. Like tires, serpentine belt ribs wear slowly and may not show signs of wear. However, they can appear to be in good condition when they’re actually ready to fail.

Replace the belt if you see:

  • Ribs that are rounded over or flattened out.
  • Cracks in the belt ribbing spaced every 1/8-inch or so. Small cracks are OK, but spider web-like cracking on the surface signals extreme wear.
  • Pieces of the belt ribbing missing or frayed.
  • The smoother side of the belt is glossy or shiny; has rounded edges or chunks missing; has glazing, large cracks, peeling or fraying.

A Gates belt wear gauge can measure serpentine belt ribs to determine if the belt should be replaced. Contact Gates and ask for part number 443-0382-R5.

Although newer EPDM belts can last twice as long as neoprene belts, inspect belts for wear as part of your regularly scheduled maintenance service.

Replace belts if contaminated; when installing a new idler or tensioner; or making major repairs like replacing a leaking water pump or worn timing belt. Unless you just replaced the drive belt, consider installing a new one if your alternator, power steering pump or AC compressor needs replacing.

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Bob Lacivita
Bob Lacivita is an award-winning ASE and General Motors auto technician, educator and freelance writer who has written about DYI car repairs and vehicle maintenance topics. His work has been featured in The Family Handyman, a Reader's Digest book and Classic Bike Rider magazine. He has been a career and technical educator for 25 years teaching automotive technology, as well as writing state, federal and organizational foundation grants. He also helped design a unique curriculum delivery model that integrates rigorous, relevant academic standards seamlessly into career and technical education.