This procedure covers removal and replacement of the coolant bypass pipe on the 3.5L EcoBoost V6 engine, which routes coolant between the engine block and thermostat housing.

Warnings

Tools required

Parts

• Coolant bypass pipe assembly × 1 — Ford OEM or Motorcraft
• Bypass pipe O-rings × 2 — Usually included with pipe assembly
• Hose clamps (if reusing is not advisable) × 2 — Worm-drive or spring clamps to OEM spec

Fluids

• Motorcraft Orange Coolant — 2 qt

Preparation

1. Ensure engine is completely cold to the touch
2. Park vehicle on level surface and engage parking brake
3. Place drain pan under radiator drain petcock location
4. Remove engine cover by pulling upward on clips (if equipped)
5. Locate the coolant bypass pipe on driver side of engine between block and thermostat housing

Procedure

1. 1

   Drain cooling system
   Open the radiator drain petcock at the bottom of the radiator driver side. Allow coolant to drain into pan. If your radiator has a drain plug instead of petcock, remove it completely. You do not need to drain the entire system, but draining 2-3 quarts will minimize spillage.
   ⚠Coolant may drain quickly initially. Monitor drain pan capacity.
   Torque spec

   Drain Petcock8 Nm (6 lb-ft)
2. 2

   Relieve system pressure
   Carefully remove the coolant reservoir cap to relieve any residual pressure in the system. Wipe up any coolant around the filler neck.
3. 3

   Disconnect lower bypass hose
   Locate the lower coolant hose connected to the bypass pipe near the engine block. Using hose clamp pliers or screwdriver, loosen or release the hose clamp. Slide clamp back on hose away from connection point. Twist and pull hose off the bypass pipe nipple. Additional coolant will drain; keep drain pan positioned.
   ℹ️Mark hose orientation with tape if connections are not obviously different sizes to aid reassembly.
4. 4

   Disconnect upper bypass hose
   Locate the upper coolant hose connection at the thermostat housing side of the bypass pipe. Loosen or release the hose clamp, slide it back on the hose, then twist and pull the hose off the bypass pipe. More coolant will drain.
5. 5

   Remove bypass pipe mounting fasteners
   The bypass pipe is secured to the engine block with two 8mm or 10mm bolts (depending on production date). Remove these bolts completely and set aside. Note their length and position if they differ.
6. 6

   Remove bypass pipe assembly
   Carefully pull the bypass pipe assembly away from the engine block and thermostat housing. The pipe has O-ring seals at both connection points. Wiggle and twist gently while pulling to break the O-ring seal. Remove pipe from engine bay.
   ⚠Do not pry against aluminum engine components or thermostat housing. Use only hand pressure to avoid damage.
7. 7

   Clean sealing surfaces
   Inspect the mating surfaces on the engine block and thermostat housing where the bypass pipe connects. Remove any old O-ring material, debris, or corrosion using a plastic scraper or clean rag. Do not scratch or gouge the aluminum sealing surfaces. Wipe clean with a lint-free rag.
8. 8

   Install new O-rings on bypass pipe
   Remove old O-rings from the new bypass pipe (or install new O-rings if reusing pipe). Lightly coat new O-rings with clean coolant to aid installation. Seat O-rings fully in their grooves on both ends of the bypass pipe.
   ℹ️Do not use petroleum-based lubricants on O-rings as they can degrade rubber and contaminate coolant.
9. 9

   Install bypass pipe assembly
   Carefully align the bypass pipe with both the engine block and thermostat housing connection points. Push the pipe straight into position, ensuring both O-rings seat properly. The pipe should sit flush against mounting points without gaps.
10. 10

    Install mounting fasteners
    Install the bypass pipe mounting bolts finger-tight first to ensure proper alignment. Then tighten bolts evenly to 16 Nm (12 lb-ft) using torque wrench if bolts thread into housing, or to manufacturer specification if they secure a bracket.
    ⚠Do not overtighten fasteners into aluminum housing. Use torque wrench to prevent thread damage.
    Torque spec

    Housing Bolts16 Nm (12 lb-ft)
11. 11

    Reconnect coolant hoses
    Reconnect both the upper and lower coolant hoses to the bypass pipe nipples. Ensure hoses are seated fully onto the pipe nipples. Position hose clamps over the hose/nipple connection point and tighten to 3 Nm (2 lb-ft) if using worm-drive clamps, or compress spring clamps fully into position.
    Torque spec

    Hose Clamps3 Nm (2 lb-ft)
12. 12

    Close drain and refill cooling system
    Close the radiator drain petcock hand-tight (8 Nm / 6 lb-ft if using torque wrench). Begin filling the cooling system through the reservoir with Motorcraft Orange Coolant. Fill slowly to allow air to escape. Locate and open the cooling system bleed screw (typically on thermostat housing or upper hose) to 8 Nm (6 lb-ft) and leave open during filling until coolant flows steadily without bubbles, then close.
    ℹ️The 3.5L EcoBoost system requires bleeding to prevent air pockets. Consult owner's manual for exact bleed screw location if unclear.
    Torque spec

    Drain Petcock8 Nm (6 lb-ft)

    Bleed Screw8 Nm (6 lb-ft)
13. 13

    Burp cooling system
    With reservoir filled to COLD MAX line and bleed screw closed, start the engine and allow it to idle with heater on full hot. Monitor coolant level and add as needed as air purges from system. Run until engine reaches normal operating temperature and radiator fan cycles on. Shut off engine and recheck coolant level when cool.
    ⚠Watch temperature gauge closely. If engine begins to overheat, shut off immediately and recheck for air pockets or leaks.

Reassembly

1. Reinstall engine cover if removed
2. Top off coolant reservoir to COLD MAX line after engine has fully cooled from test run
3. Inspect all connections for signs of seepage after 24 hours of driving

Verification

• Check for coolant leaks around both bypass pipe O-ring connections and hose clamps with engine at operating temperature
• Verify no overheating occurs during test drive and temperature gauge reads normal
• Confirm heater produces hot air at idle and while driving
• Recheck coolant level when cold after first drive cycle; top off if needed
• Inspect ground under vehicle for coolant drips after overnight parking

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