Most Likely Causes:
* Belt Wear/Slipping: This is the most frequent cause. An old, cracked, or glazed belt will slip on the pulleys, causing a squeal, especially when starting or under load (acceleration). Solution: Visually inspect the belt for cracks, glazing (shiny, glassy surface), fraying, or significant wear. If damaged, replace it. A new belt is inexpensive.
* Idler Pulley or Tensioner Pulley Bearing Failure: These pulleys guide the belt and maintain tension. A worn bearing in either will make a squealing noise. You might hear it more at idle or when the engine is cold. Solution: Inspect these pulleys for play or roughness. If you can feel play (wobble) in the pulley or hear a grinding noise when rotating it by hand, replace the pulley.
* Alternator Bearing Failure: Similar to the idler/tensioner pulleys, a worn alternator bearing will squeal. This often gets worse as the alternator gets hotter. Solution: Inspect the alternator pulley for play. If the bearing is bad, the alternator needs to be replaced or rebuilt.
* Power Steering Pump Bearing Failure: A squealing noise that's more prominent when turning the steering wheel points to a problem with the power steering pump. Solution: Check the power steering fluid level. Low fluid can cause squealing. If the fluid is fine, the pump bearing might be failing and needs replacement.
* Water Pump Bearing Failure: Less common but possible. A bad water pump bearing will often make a squeal, especially when the engine is cold. Solution: Inspect the water pump pulley for play. A bad water pump requires replacement.
Troubleshooting Steps:
1. Inspect the Belt: This is the first thing to do. A visual inspection often reveals the problem.
2. Check Belt Tension: Use your hand to press on the belt midway between two pulleys. There should be some deflection (give), but not too much. Consult your owner's manual for the correct amount of deflection. Improper tension can cause squealing.
3. Listen Carefully: Try to pinpoint the location of the squeal. Is it coming from the alternator, power steering pump, or a pulley? This will help narrow down the problem.
4. Check Fluids: Ensure your power steering fluid is at the correct level.
5. Start the Engine and Listen: Observe the squeal during various driving conditions (idle, acceleration, turning). This will give you more clues.
6. Spray Lubricant (Temporary Fix): As a temporary measure, carefully spray a little belt dressing (NOT WD-40) onto the belt while the engine is running. If the squeal stops temporarily, it likely points to a worn or slipping belt. This is ONLY a temporary fix; replace the belt.
Important Note: If you're not comfortable working on your vehicle, take it to a mechanic. Ignoring a squealing belt can lead to more serious damage, including broken belts and damaged pulleys. A broken serpentine belt will leave you stranded.
