* Belt Wear or Degradation: The most common cause. An old, worn, cracked, or glazed belt loses its grip on the pulleys. The slippage causes the squeal, especially when the engine's demand on the belt is low (like at idle) because there's less tension to maintain grip.
* Loose Belt: Insufficient tension on the belt prevents proper contact with the pulleys. This is a common problem that can arise after belt replacement if not properly tensioned or due to a worn tensioner pulley.
* Dirty or Greasy Belt: Oil, grease, or other contaminants on the belt reduce its friction and grip, leading to slippage and squealing.
* Worn or Damaged Pulley: A pulley with a grooved, worn, or misaligned surface won't grip the belt properly, causing squealing. This is more common with the alternator, power steering pump, or air conditioning compressor pulleys.
* Seized or Failing Pulley Bearing: A bearing in one of the pulleys might be seizing up. This will restrict the pulley's rotation and cause increased friction, leading to the squeal. You might also notice a rough feel or noise when turning the pulley by hand (if possible and safe).
* Water Pump Bearing: Similar to a seized pulley bearing, a failing water pump bearing can also create a squeal.
Troubleshooting Steps:
1. Inspect the Belt: Check the belt for cracks, glazing (shiny appearance), fraying, or other signs of wear. If it's visibly damaged, replace it.
2. Check Belt Tension: Most serpentine belts have a tensioner pulley. You may be able to check the tension by pressing on the belt midway between two pulleys. It should have some resistance but shouldn't be extremely tight. Consult your vehicle's repair manual for the proper tension specifications.
3. Clean the Belt: If the belt looks okay, try cleaning it with a belt dressing specifically designed for automotive belts (avoid using anything else).
4. Inspect Pulleys: Visually inspect all pulleys driven by the belt for any damage, grooves, or excessive wear. Try to feel for any play or roughness in the pulley bearings.
5. Listen Carefully: Try to pinpoint the source of the squeal. This will help determine which pulley or component might be the culprit.
If you're not comfortable performing these checks yourself, it's best to take your vehicle to a qualified mechanic for diagnosis and repair. Ignoring a squealing belt can lead to belt failure, which can cause damage to other components and potentially leave you stranded.
