Replace the coolant bypass pipe on the 3.5L EcoBoost engine, which connects coolant flow between the engine block and thermostat housing.

Warnings

Tools required

Parts

• Coolant bypass pipe assembly × 1 — Use OEM Ford specification
• Bypass pipe O-rings × 2 — Usually included with pipe assembly
• Thermostat housing gasket × 1 — Use OEM Ford specification
• Hose clamps (if worn or damaged) × 2 — Use OEM specification

Fluids

• Motorcraft Orange Coolant — 2 qt

Preparation

1. Ensure engine is completely cold (at least 2 hours after last operation)
2. Park vehicle on level ground and engage parking brake
3. Disconnect negative battery cable to prevent accidental fan operation
4. Remove engine cover by pulling upward on front and rear tabs
5. Place drain pan under radiator and open drain petcock to drain coolant below engine level
6. Take photos of hose routing and electrical connections before disassembly

Procedure

1. 1

   Remove air intake system
   Disconnect the mass airflow sensor electrical connector. Loosen the clamp at the throttle body and the clamp at the air filter housing. Remove the entire air intake tube assembly and set aside. This provides access to the top of the engine valley.
2. 2

   Disconnect coolant hoses from bypass pipe
   Locate the coolant bypass pipe in the center of the engine valley. Use hose clamp pliers or a flathead screwdriver to reposition the hose clamps away from the pipe connections. Twist and pull the coolant hoses off the bypass pipe fittings. Expect residual coolant spillage; use shop towels to contain.
   ⚠Hoses may be stuck due to age. Twist gently while pulling to avoid tearing the hose. If severely stuck, carefully cut the hose and replace it.
3. 3

   Remove thermostat housing bolts (partial)
   The bypass pipe connects to the underside of the thermostat housing. Remove the two accessible bolts securing the thermostat housing using a 8mm socket. You may need to loosen but not fully remove the housing to access the bypass pipe, depending on the specific configuration. Note bolt locations for reassembly.
   Torque spec

   Housing Bolts16 Nm (12 lb-ft)
4. 4

   Remove bypass pipe mounting fasteners
   Locate and remove the bolt(s) or clips securing the coolant bypass pipe to the engine block or cylinder head. The exact mounting configuration varies, but typically uses one or two 10mm bolts. Carefully support the pipe as you remove the final fastener.
5. 5

   Extract coolant bypass pipe
   Carefully maneuver the bypass pipe out of the engine valley. The pipe has O-ring seals at connection points that may bind. Gently twist and pull with steady pressure. Work slowly to avoid breaking the pipe or damaging sealing surfaces on the engine block and thermostat housing.
   ⚠The pipe fits in a confined space with limited clearance. Forcing the pipe can crack it or damage aluminum sealing surfaces. If stuck, apply gentle heat with a heat gun to soften O-rings.
6. 6

   Clean sealing surfaces
   Remove old O-rings from the pipe connection points on the engine block and thermostat housing using a pick tool. Clean all sealing surfaces thoroughly with a razor blade or gasket scraper, removing all residue, corrosion, or old gasket material. Wipe clean with shop towels. Inspect surfaces for pitting or damage that could prevent proper sealing.
   ⚠Be extremely careful not to gouge or scratch aluminum sealing surfaces. Deep scratches will cause coolant leaks. Use plastic scrapers on delicate surfaces if available.
7. 7

   Prepare new bypass pipe
   Verify the new bypass pipe matches the old part exactly. Install new O-rings onto the pipe fittings (if not pre-installed). Lightly lubricate all O-rings with fresh coolant or approved O-ring lubricant to ease installation and prevent tearing during insertion.
8. 8

   Install new bypass pipe
   Carefully guide the new bypass pipe into position in the engine valley. Align the pipe with the mounting points on the engine block and the thermostat housing connection. Press firmly to seat the O-rings into their respective bores. Ensure the pipe is fully seated before installing fasteners.
   ℹ️The pipe should slide into place with moderate pressure. Excessive force indicates misalignment. Remove and reposition rather than forcing.
9. 9

   Install bypass pipe mounting fasteners
   Install and hand-tighten the mounting bolt(s) that secure the bypass pipe to the engine block. Torque to specification using the appropriate torque value for housing bolts if connecting to a housing structure.
   Torque spec

   Housing Bolts16 Nm (12 lb-ft)
10. 10

    Reinstall thermostat housing
    Install a new thermostat housing gasket if removed. Position the thermostat housing over the bypass pipe connection and align bolt holes. Install the thermostat housing bolts and torque in a criss-cross pattern to ensure even gasket compression.
    Torque spec

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

    Reconnect coolant hoses
    Slide the coolant hoses onto the bypass pipe fittings, ensuring they are fully seated against the pipe shoulders. Position new or existing hose clamps over the hose-to-pipe connections. Tighten hose clamps to specification using a torque-limiting screwdriver or carefully with a nut driver.
    ⚠Over-tightening hose clamps can cut into hoses or crack plastic pipe fittings. Use specified torque or hand-tighten only until snug.
    Torque spec

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

    Reinstall air intake system
    Reinstall the air intake tube assembly, ensuring proper alignment at both the air filter housing and throttle body. Tighten both clamps securely. Reconnect the mass airflow sensor electrical connector with an audible click.
13. 13

    Refill and bleed cooling system
    Close the radiator drain petcock and torque to specification. Locate the cooling system bleed screw on top of the thermostat housing or degas bottle. Open the bleed screw. Slowly fill the cooling system with Motorcraft Orange Coolant through the degas bottle until coolant flows from the bleed screw without bubbles. Close bleed screw to specification. Continue filling to the COLD FILL level. Install degas bottle cap.
    ℹ️Failure to properly bleed air from the system will result in overheating and potential engine damage. Ensure steady coolant flow from bleed screw before closing.
    Torque spec

    Drain Petcock8 Nm (6 lb-ft)

    Bleed Screw8 Nm (6 lb-ft)
14. 14

    Burp cooling system and check for leaks
    Reconnect negative battery cable. Start the engine and allow it to reach operating temperature with the heater on high. Monitor coolant level in the degas bottle and add as needed. Rev engine to 2500 RPM several times to purge remaining air. Check all connections around the bypass pipe, thermostat housing, and hoses for coolant leaks. Shut off engine and allow to cool, then recheck coolant level and top off to COLD FILL line.
    ⚠Keep hands and tools clear of the engine cooling fan, which may activate at any time when the engine is running.

Reassembly

1. Reinstall engine cover by aligning tabs and pressing down until clips engage
2. Verify all hose clamps are properly tightened and positioned
3. Ensure no tools or shop towels are left in the engine compartment
4. Double-check coolant level after vehicle has been driven and cooled

Verification

• Start engine and verify no coolant leaks from bypass pipe connections, thermostat housing, or hoses
• Confirm engine reaches normal operating temperature (approximately 195-205°F) without overheating
• Verify heater produces hot air at idle and under acceleration, indicating proper coolant flow
• Check degas bottle coolant level after engine cools - should be at COLD FILL line
• Inspect engine valley and ground under vehicle for coolant drips after overnight sit
• Monitor coolant level over the next few days and top off if necessary as air continues to purge from system

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