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Tim West
Tim West, ASE Certified Technician
Category: Ford
Satisfied Customers: 4638
Experience:  ASE Certified Service manager of Firestone
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My 2007 Taurus with 90,000km had squealing serpentine belt.

Resolved Question:

My 2007 Taurus with 90,000km had squealing serpentine belt. One shot of penetrating lubricant silenced it for less than an hour. I had new belt installed on May 10 and all seemed fine for about a week then squeal returned with a vengence and now is constant. Since a bit of lube on the belt silences the squeal the problem is not a bearing. Are the plastic pullies the problem? How do I fix the problem?
Submitted: 6 years ago.
Category: Ford
Expert:  Tim West replied 6 years ago.
Thanks for visiting Just Answer,
Take the belt off and start the vehicle, does it squeal?
If the squeal does not go away, there could be an issue with the camshaft synchronizer. Do not over look this.
I understand belt dressing quiets the belt.
If not, let's move on with belt inspection. A belt tensioner or idler pulley can also cause the noise. Try using a long screw driver as a "stethescope" and listen to the ppulleys and try to compare with the others to locate a possible tensioner or pulley.
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Component Tests

Drive Belt Noise/Flutter
Drive belt chirp occurs due to pulley misalignment or excessive pulley runout. It can be the result of a damaged or an incorrectly aligned grooved pulley.

To correct, determine the area where the noise comes from. Check each of the pulleys in that area with a straightedge to the crankshaft pulley. Look for accessory pulleys out of position in the fore/aft direction or at an angle to the straightedge.

CAUTION: Do not apply any fluids or belt dressing to the accessory drive belt or pulleys.

Drive belt squeal may be an intermittent or constant noise that occurs when the drive belt slips on an accessory pulley under certain conditions.

A short intermittent squeal may occur during engine start-up and shut down or during very rapid engine acceleration and decelerations, such as:

  • wide open throttle 1-2 and 2-3 shifts or 2-3 and 3-4 back out shifts on automatic transmissions.
  • wide open throttle 1-2 and 2-3 shifts and any combination of rapid downshifting on manual transmissions.

These special short-term transient events are expected, and are due to the higher system inertias required to meet the electrical and cooling demands of today's vehicle systems. Constant or re-occurring drive belt squeal can occur under these conditions:

  • if the A/C discharge pressure goes above specifications:
  • the A/C system is overcharged.
  • the A/C condenser core airflow is blocked.
  • if the A/C OFF equalized pressure (the common discharged and suction pressure that occurs after several minutes) exceeds specifications.
  • if any of the accessories are damaged or have a worn or damaged bearing. All accessories should be rotatable by hand in the unloaded condition, if not, inspect the accessory.
  • if there is evidence of fluid contamination on the accessory drive belt. When the drive belt has been exposed to fluid contamination during vehicle operation, such as leaks from the power steering system, A/C system or cooling system, clean all pulleys with soap and water, rinse with clean water and install a new accessory drive belt. If the drive belt has been exposed to fluids in a localized area during routine vehicle service, such as replacement of hoses or fluids, the drive belt and pulleys should be washed with soap and water immediately (prior to starting the engine), and rinsed with clean water.
  • if the accessory drive belt is too long. A drive belt that is too long will allow the accessory drive belt tensioner arm to go all the way to the arm travel stop under certain load conditions, which will release tension to the drive belt. If the accessory drive belt tensioner indicator is outside the normal installation wear range window, install a new accessory drive belt.
  • NOTE: The accessory drive belt tensioner arm should rotate freely without binding.

Install a new accessory drive belt tensioner if the drive belt tensioner is worn or damaged.

Incorrect Drive Belt Installation

CAUTION: Incorrect accessory drive belt installation will cause excessive drive belt wear and can cause the drive belt to come off the pulleys.

Non-standard accessory drive belts can track differently or incorrectly. If an accessory drive belt tracks incorrectly, install a new accessory drive belt to avoid performance failure or loss of the drive belt.

Incorrect Installation

Correct Installation


With the engine running, check accessory drive belt tracking on all pulleys. If the edge of the accessory drive belt rides beyond the edge of the pulleys, noise and premature wear will occur. Make sure the accessory drive belt rides correctly on the pulley. If an accessory drive belt tracking condition exists:

  • Visually check the accessory drive belt tensioner for damage, especially the mounting pad surface. If the accessory drive belt tensioner is not installed correctly, the mounting surface pad will be out of position. This will result in chirp and squeal noises.
  • With the engine running, visually observe the grooves in the pulleys (not the pulley flanges or the pulley forward faces) for excessive wobble. Install new components as necessary.
  • Check all accessories, mounting brackets and the accessory drive belt tensioner for any interference that would prevent the component from mounting correctly. Correct any interference condition and recheck the accessory drive belt tracking.
  • Tighten all accessories, mounting brackets and accessory drive belt tensioner retaining hardware to specification. Recheck the accessory drive belt tracking.

Belt Tensioner - Mechanical
The only mechanical check that needs to be made is a check for tensioner stick grab or bind.

  1. With the engine OFF, check routing of the accessory drive belt.
  2. NOTE: The accessory drive belt tensioner spring is very strong and requires substantial force to release. Using a suitable, commercially available serpentine belt tensioner release tool, release the tension on the belt and detach the accessory drive belt in the area of the tensioner.
  3. Using the suitable, commercially available serpentine belt tensioner release tool, move the tensioner from its relaxed position, through its full stroke and back to the relaxed position to make sure there is no stick, grab or bind, and to make sure that there is tension on the tensioner spring.
  4. Rotate the tensioner pulley by hand and check for a binding, contaminated or seized condition. Install a new accessory drive belt tensioner if necessary.
  5. Inspect the area surrounding the accessory drive belt tensioner for oil leaks or contamination and repair any leaks. Install a new accessory drive belt tensioner as necessary.
  6. If the accessory drive belt tensioner meets the above criteria, proceed to testing the tensioner dynamically. If the accessory drive belt tensioner does not meet the above criteria, install a new tensioner.

Belt Tensioner - Dynamics
The accessory drive belt tensioner can be checked dynamically as follows:

  1. With the engine running, observe the accessory drive belt tensioner movement. The accessory drive tensioner should move (respond) when the air conditioning clutch cycles (if equipped), or when the engine is accelerated rapidly. If the accessory drive belt tensioner movement is excessive without air conditioning clutch cycling or engine acceleration, check belt rideout. Excessive belt rideout (uneven depth of grooves in the belt) can cause excessive accessory drive belt tensioner movement. Check rideout condition by installing a new belt. If excessive accessory drive belt tensioner movement still exists, install a new accessory drive belt tensioner.
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