Before you go through all the trouble of replacing the drive belt tensioner, I would make sure that you need one.
Here is some info from the Ford TSP (Technical Service Publication):
Drive belt squeal is an intermittent noise that occurs when the drive belt slips on a pulley during certain conditions such as:
- engine start-up.
- rapid engine acceleration.
- A/C clutch engagement.
Drive belt squeal can occur under the following conditions:
* The A/C discharge pressure goes above 2895 kPa (420 psi). This can occur if:
-- The A/C system is overcharged.
-- The A/C condenser airflow is blocked.
-- The engine cooling fan is not engaging fully at idle.
* Any of the accessories are damaged, have a worn or damaged bearing or internal torsional resistance above normal for any reason. All of the accessories should be rotatable by hand in the unloaded condition. If any are not, the accessory should be inspected.
* Note: If fluid does get on the drive belt during service, clean the drive belt with soap and water and thoroughly rinse with clean water. The drive belt does not have to be replaced if no apparent damage has occurred.
If fluids get on the drive belt. This would include power steering fluid, engine coolant, engine oil and air conditioning system lubricant.
* The drive belt is too long. It will be evident by the arm of the drive belt tensioner resting on the stop. If the drive belt tensioner is resting on the stop, replace the drive belt.
* Note: The drive belt tensioner arm should rotate freely without binding.
The drive belt tensioner is worn or damaged.
They sell cans of drive belt dressing at most auto stores to get rid of the sound that you are talking about. You might want to try that first.
