Chances are the noise you hear (especially if the pitch changes as you accellerate the engine speed) is the serpentine belt and tensioner assembly.
You can perform this simple test to see if only the belt needs to be replaced, or if your pulleys are wore out as well. Take a yellow crayon and with engine at idle, allow the crayon to drag across the belt forming a yellow line. Just be sure you watch your fingers and don't get anything tangled up in the rotating parts. You don't need too much crayon wax on the belt. Just a little to see if it makes a difference to the noise.
Get some crayon wax on the "flat" surface of the belt, first. Your post indicates having a 4-cyl engine, which does not exist in the 2000 Taurus. But if you have the most-common 12-valve Single OH Valve V-6, the flat side of the belt rides along the tensioner pulley. If the noise continues without changing, then the noise is happening on the ribbed side engaging to various ribbed pulleys such as the A/C compressor or alternator.
It's common for the tensioner to wear out, causing misalignment, and the squealing noise.
So, in conclusion, you can try the repair in two steps if the squealing noise goes away with the crayon test: Take a chance and replace belt only. But noise may return. Or replace belt and tensioner assembly in one job. Have the mechanic inspect idler pulley as well while belt is off vehicle.
If the squealing noise makes no difference after yellow crayon is applied to belt flat surface, just replace belt (AND/OR) inspect alternator pulley bearings while belt is off. Spin alternator to listen for any bearing noise, indicating dry bearings.
And why yellow crayon? Color Yellow just makes it easy to see how much wax has already been applied against the black belt. Use crayon sparingly.
Wednesday, March 4th, 2009 AT 10:25 PM