* Worn Serpentine Belt: This is the most common cause. A cracked, glazed, or otherwise worn belt will squeal, especially when cold and under initial tension during engine startup. The squeal is often worse when the engine is cold because the belt is stiffer.
* Belt Tensioner: The tensioner keeps the belt properly taut. A failing tensioner might not be applying enough tension, leading to slippage and the characteristic whine. A seized or failing bearing within the tensioner will also cause noise.
* Belt Idler Pulley: Similar to the tensioner, a worn or seized bearing in an idler pulley will cause a whine, especially at startup.
* Power Steering Pump: A failing power steering pump can cause a whine, often more pronounced at low speeds or when turning the steering wheel, but it can also manifest as a whine at startup.
* Alternator: A failing alternator bearing can also create a whining sound, particularly at startup.
* Water Pump: While less common, a worn water pump bearing can produce a whine.
* Contaminants on the Belt: Oil, grease, or other contaminants on the belt can cause slippage and noise.
Troubleshooting Steps:
1. Visual Inspection: Carefully examine the serpentine belt for cracks, glazing, fraying, or other signs of wear. Check all pulleys (tensioner, idler, alternator, power steering pump, water pump) for any visible damage or signs of bearing failure (play, roughness, etc.).
2. Listen Carefully: Try to pinpoint the source of the noise. Is it coming from the tensioner, a specific pulley, or the belt itself? This can help narrow down the problem.
3. Check Belt Tension: (Use caution – belts are under tension) If you're comfortable, try to gently push on the belt midway between two pulleys. It should have some resistance, but not be overly tight. Excessive slack or too much tension can both cause problems.
What to do:
If you're not comfortable performing these checks yourself, take your Lexus RX 300 to a qualified mechanic. Ignoring a belt whine can lead to more serious damage as the belt could break, leaving you stranded and potentially causing damage to other components.
It's crucial to address this issue promptly to avoid more significant problems and potential engine damage.
