Serpentine Belt Tensioner

This procedure covers the removal and replacement of the serpentine belt tensioner on the 3.5L V6 EcoBoost engine, requiring partial disassembly of front engine accessories.

Warnings

Tools required

Parts

• Serpentine belt tensioner assembly × 1 — Use OEM Ford specification for 3.5L EcoBoost
• Serpentine belt (if worn or damaged) × 1 — Use OEM Ford specification for 3.5L EcoBoost

Preparation

1. Park vehicle on level ground and engage parking brake
2. Allow engine to cool completely (minimum 2 hours after operation)
3. Disconnect negative battery terminal and secure away from battery post
4. Photograph serpentine belt routing from multiple angles for reference
5. Remove engine cover by pulling upward on the four retaining grommets

Procedure

1. 1

   Remove engine cover and access components
   With the engine cover removed, inspect the serpentine belt routing and locate the belt tensioner on the front passenger side of the engine. Verify you have clear photographic reference of the belt routing path.
2. 2

   Release belt tension and remove serpentine belt
   Using a 15mm socket and breaker bar on the tensioner center bolt, rotate the tensioner clockwise to release tension. Slide the serpentine belt off the nearest pulley while maintaining tension control, then slowly release the tensioner. Remove the belt completely from all pulleys, noting any unusual wear patterns.
3. 3

   Remove air intake components for access
   Loosen the clamp at the throttle body and disconnect the air intake tube. Remove the 10mm bolts securing the air filter housing if additional clearance is needed. Move components aside to provide clear access to the tensioner mounting area.
   Torque spec

   Cover Bolts19 Nm (14 lb-ft)
4. 4

   Disconnect tensioner electrical connector if equipped
   Some 3.5L EcoBoost engines have a sensor on the tensioner assembly. If present, press the release tab and disconnect the electrical connector. Move the wiring harness aside to prevent damage during removal.
5. 5

   Remove tensioner mounting bolt
   Using a 15mm socket, remove the single mounting bolt securing the tensioner to the engine block. The bolt threads into the engine front cover. Support the tensioner with one hand as you remove the bolt to prevent it from falling into the engine compartment.
6. 6

   Extract tensioner assembly
   Carefully maneuver the tensioner assembly out of the engine bay. You may need to angle it slightly to clear surrounding components. Inspect the mounting surface on the engine for any damage or debris and clean if necessary.
7. 7

   Inspect related components
   With the tensioner removed, inspect all serpentine belt pulleys for smooth rotation, unusual noise, or bearing wear. Check the removed tensioner pulley for roughness or play. Verify the new tensioner pulley rotates smoothly and spring tension feels consistent.
8. 8

   Install new tensioner assembly
   Position the new tensioner assembly onto the engine block mounting point, aligning the bolt hole. Thread the mounting bolt by hand several turns to ensure proper thread engagement before using tools. Avoid cross-threading by ensuring the tensioner is properly seated against the mounting surface.
   Torque spec

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

   Torque tensioner mounting bolt
   Using a torque wrench, tighten the tensioner mounting bolt to 55.0 Nm (41 lb-ft). Verify the tensioner sits flush against the mounting surface and does not move when actuated.
   Torque spec

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

    Reconnect electrical connector if equipped
    If the tensioner has an electrical connector, plug it back in until it clicks securely. Ensure the wiring harness is properly routed and secured away from moving components and heat sources.
11. 11

    Install serpentine belt
    Route the new or existing serpentine belt around all pulleys except one (typically the alternator or idler pulley) following your reference photograph. Using a 15mm socket and breaker bar, rotate the tensioner clockwise to create slack, then slip the belt onto the final pulley. Carefully release the tensioner to apply proper tension to the belt.
12. 12

    Verify belt alignment and routing
    Inspect the entire belt path to ensure the belt is properly seated in all pulley grooves and aligned correctly. The belt should sit centered on each pulley with no twisting or overlap. Compare against your routing photograph to verify correctness.
13. 13

    Reinstall air intake components
    Reinstall the air filter housing and secure with 10mm bolts if removed. Reconnect the air intake tube to the throttle body and tighten the clamp securely. Ensure no tools or parts remain in the engine compartment.
    Torque spec

    Cover Bolts19 Nm (14 lb-ft)

Reassembly

1. Reinstall the engine cover by pressing firmly on each grommet location until seated
2. Reconnect the negative battery terminal and tighten securely
3. Double-check that all tools have been removed from the engine compartment

Verification

• Start the engine and observe the serpentine belt operation for 30-60 seconds, checking for proper tracking on all pulleys
• Listen for any unusual squealing, chirping, or rattling noises that could indicate misalignment or improper tension
• Verify the belt remains centered on all pulleys and does not walk off to either side during operation
• Check that all accessories (alternator, water pump, A/C compressor) are functioning normally
• Rev the engine to approximately 2000 RPM briefly and verify belt remains stable with no slippage or noise

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