1. Belt Tension:
* Check the belt tension: This is the most common cause. A loose belt will slip and squeal, especially when the alternator is under load (like when you turn on headlights or the AC). Use your hand to press firmly on the middle of the longest span of the belt between pulleys. It should deflect only slightly (usually about 3/8" to 1/2" depending on the car and belt). If it deflects too much, the belt is too loose.
* Adjust the belt tensioner: Most modern vehicles have an automatic belt tensioner. If yours is adjustable, consult your car's repair manual or an online resource specific to your make and model. Improper adjustment can damage the tensioner or alternator. If it's not adjustable, the problem likely lies elsewhere.
2. Belt Condition:
* Inspect the belt: Carefully examine the belt for cracks, glazing (shiny, smooth surface), fraying, or any other signs of wear. A worn or damaged belt needs to be replaced.
* Check for debris: Look for any debris (like dirt, leaves, or grease) that might be preventing proper contact between the belt and the pulleys. Clean the belt and pulleys thoroughly if needed.
3. Pulley Alignment:
* Check pulley alignment: Though less common, misaligned pulleys can cause belt slippage and squealing. Visually inspect all pulleys to ensure they're properly aligned and spinning freely. Worn or damaged pulleys will need to be replaced. This is harder to diagnose without specialized tools.
4. Alternator Installation:
* Double-check the alternator installation: While less probable with a new alternator, make sure it's securely mounted and all connections are tight. A loose connection could cause a squeal.
5. Lubrication (Last Resort):
* Do NOT use oil or grease on the belt: While some people suggest this, it's a bad idea. It will attract more dirt and damage the belt and pulleys further. Use belt dressing specifically designed for serpentine belts. Apply sparingly.
If the squeal persists after checking these points:
* Consult a mechanic: If you're not comfortable working on your car, or if the problem isn't easily identifiable, take your car to a qualified mechanic. They have the tools and expertise to diagnose the issue properly.
Remember safety first! Always disconnect the negative battery terminal before working on your car's electrical system. If you're unsure about any step, consult your car's repair manual or seek professional help.
