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Decoding Your Car’s Noisy Belts: What They’re Telling You

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A car engine belt that’s squealing or chirping isn’t just an annoying sound – it’s a signal that something might be amiss in your vehicle’s underbelly. For many years, auto mechanics have known that a noisy serpentine belt should never be ignored. It’s not quite like the dreaded check engine light, but it’s your car’s way of signaling that something isn’t right in the drive belt system.

Understanding these belt noises can be the difference between minor maintenance and major repairs. So, let’s dive into the world of car belts and the language they speak through their distinct sounds.

Understanding Belt Noises
Serpentine drive belts can produce a range of odd noises. They can squeak, squeal, chirp, or clunk, mimicking issues with engine-driven accessories or engine bearings. These sounds can be deceiving, even for seasoned mechanics, often leading to costly misdiagnoses.

Squeals and chirps are the most common serpentine belt noises and often result from different problems.

Chirping presents as a series of sharp pulsing sounds. As you accelerate, the chirp pitch and volume stay constant.

Belt squeal, on the other hand, produces a high-pitched shriek that can increase in volume with engine speed, while the pitch remains consistent.

Reasons for Belt Noise
Beyond typical wear and tear, any malfunctioning component in a drive belt system can lead to belt noise or premature wear. Fluid leaks like oil, antifreeze, or power steering fluid onto a belt can quickly cause it to deteriorate. It’s crucial to fix the leak and thoroughly clean the pulleys before fitting a new belt.

Now, here’s what to inspect:

For chirping noises:

  • Verify that the pulleys are aligned properly using a straight edge or laser alignment tool.
  • Ensure all mounting brackets, pulleys, tensioners, and idler wheels are securely fastened to the engine.
  • Check that all accessory pulleys and idler wheels spin freely, showing no signs of excessive wear, rust, flat spots, or burrs.
  • Examine the component pulleys, like those for air conditioning, power steering, alternator, and harmonic balancer, for wear or contamination from an old belt that may have accumulated in the grooves.

For squealing noises:
According to Gates, one of the world’s largest producers of drive belts, the primary reason for squealing belts is low belt tension.

Key points to assess:

  • Inspect the tensioner to ensure it swings freely without any squeaks, binding, clicking, or rattling from a weak, rusted, or damaged tensioner spring.
  • Check for worn belt ribs.
  • Ensure that the smooth/top side of the belt and idler wheels aren’t shiny or glazed due to overheating.
  • Look for contamination from oil, power steering fluid, antifreeze, belt dressing, or pulley grooves fouled by an old belt or damaged by debris.
  • Additionally, check if the belt is of high quality and correctly installed and that it’s the right length.

Assessing Belt Wear
Around 2000, major vehicle manufacturers started using serpentine belts made of ethylene propylene diene monomer (EPDM). Unlike traditional neoprene belts, EPDM belts can last between 50,000 and 100,000 miles. While serpentine belt ribs may wear slowly, they might not exhibit visible signs of wear. Nevertheless, they can appear to be in good condition when they’re on the verge of failing.

Replace the belt if you notice:

  • Ribs that are rounded or flattened.
  • Cracks in the belt ribbing are spaced every 1/8 inch.
  • Missing or frayed pieces of belt ribbing.
  • The smoother side of the belt is shiny and has rounded edges or chunks missing, glazing, large cracks, peeling, or fraying.

In your regular maintenance routine, inspect belts for wear. Replace belts if they’re contaminated, when you install a new idler or tensioner, or during major repairs like replacing a water pump or worn timing belt. If your alternator, power steering pump, or AC compressor needs replacing, consider installing a new drive belt unless you’ve recently replaced it.