Serpentine Belt Tensioner

This procedure covers the removal and replacement of the serpentine belt tensioner on the 3.5L EcoBoost V6 engine in 2021-2024 Ford F-150 trucks.

Warnings

Tools required

Parts

• Serpentine belt tensioner assembly × 1 — Use OEM Ford specification for 3.5L EcoBoost
• Serpentine belt × 1 — Replace if worn or contaminated

Preparation

1. Ensure engine is completely cool to the touch
2. Park vehicle on level surface and engage parking brake
3. Disconnect negative battery cable and wait 2 minutes for system discharge
4. Photograph or diagram serpentine belt routing before removal for reinstallation reference

Procedure

1. 1

   Remove engine cover
   Grasp the engine cover firmly at the rear and pull upward to disengage the retaining grommets. Lift the cover away from the engine bay and set aside.
2. 2

   Locate belt tensioner assembly
   Identify the automatic belt tensioner on the front passenger side of the engine. The tensioner is mounted to the engine block below the alternator and maintains constant tension on the serpentine belt. Verify belt routing matches your documentation before proceeding.
3. 3

   Release belt tension
   Insert a 1/2" breaker bar or serpentine belt tool into the 1/2" square drive hole on the tensioner arm. Rotate the tensioner clockwise to release belt tension. Hold tension while removing the belt from the pulleys, then slowly release the tensioner back to its resting position.
   ⚠Control the tensioner release carefully. The spring has significant force and can cause injury or damage if released suddenly.
4. 4

   Remove serpentine belt
   With tension released, slip the serpentine belt off all pulleys starting with the alternator. Remove the belt from the engine compartment. Inspect the belt for wear, cracks, glazing, or fluid contamination. Mark the belt for replacement if any defects are present.
5. 5

   Remove tensioner mounting bolt
   Using a 15mm socket with extension, remove the single bolt securing the belt tensioner to the engine block. The bolt is accessible from above. Support the tensioner with one hand while removing the bolt to prevent it from dropping.
   Torque spec

   Belt Tensioner Bolt24 Nm (18 lb-ft)
6. 6

   Remove tensioner assembly
   Carefully lift the tensioner assembly up and out of the engine bay. Note the orientation and positioning for installation of the new tensioner. Inspect the mounting surface on the engine block for debris or damage.
7. 7

   Prepare new tensioner
   Remove the new tensioner from packaging. Verify it matches the original part in appearance and mounting configuration. Check that the tensioner arm moves smoothly through its range of motion and the spring provides appropriate resistance.
8. 8

   Install new tensioner
   Position the new tensioner onto the engine block mounting location, aligning the bolt hole. Ensure the tensioner is fully seated against the engine block before installing the mounting bolt. Insert the tensioner bolt and hand-tighten initially.
   Torque spec

   Belt Tensioner Bolt24 Nm (18 lb-ft)
9. 9

   Torque tensioner bolt
   Using a torque wrench, tighten the belt tensioner mounting bolt to 55 Nm (41 lb-ft). Verify the tensioner is properly seated and does not move after torquing.
   Torque spec

   Belt Tensioner Bolt24 Nm (18 lb-ft)
10. 10

    Route serpentine belt
    Route the serpentine belt around all pulleys except the alternator, following your documented belt routing diagram. Ensure the belt is properly seated in all pulley grooves. The ribbed side of the belt should contact all grooved pulleys.
11. 11

    Install belt on alternator
    Insert breaker bar into the tensioner square drive and rotate clockwise to compress the tensioner. While holding tension, slip the belt onto the alternator pulley. Verify the belt is properly seated in all grooves, then slowly release the tensioner to apply proper belt tension.
    ⚠Ensure fingers and tools are clear of all pulleys before releasing tensioner tension.
12. 12

    Verify belt installation
    Visually inspect all pulleys to confirm the belt is properly seated in all grooves with no twists or misalignment. Manually rotate the engine one full revolution by turning the crankshaft pulley clockwise (using a socket on the center bolt). Watch for proper belt tracking and ensure the belt does not slip off any pulley during rotation.

Reassembly

1. Reinstall engine cover by aligning grommets and pressing down firmly until seated
2. Reconnect negative battery cable and tighten securely
3. Reset any fault codes if check engine light is illuminated

Verification

• Start the engine and allow it to idle, listening for any unusual belt noise or squealing
• Visually confirm the belt is tracking properly on all pulleys with no slipping
• Rev engine to approximately 2000 RPM and verify belt remains stable without flutter or slip
• Check for proper alternator charging (battery voltage should be 13.5-14.5V with engine running)
• Verify all accessories (AC, power steering, alternator) are functioning normally

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