Replace the thermostat on a 2015-2020 Ford F-150 with 3.5L EcoBoost engine to restore proper engine temperature regulation.

Warnings

Tools required

Parts

• Thermostat assembly × 1 — Use OEM Ford thermostat rated for 3.5L EcoBoost
• Thermostat housing gasket/O-ring × 1 — Usually included with thermostat
• Coolant hose clamps × 2 — Replace if corroded

Fluids

• Motorcraft Orange Coolant — 2 qt

Preparation

1. Ensure engine is completely cold (wait minimum 2 hours after last operation)
2. Park vehicle on level surface and engage parking brake
3. Place drain pan under radiator drain petcock on passenger side of radiator
4. Remove engine cover by pulling upward on front edge, then lifting off
5. Slowly loosen coolant reservoir cap to release any residual pressure, then remove cap completely

Procedure

1. 1

   Drain coolant from system
   Open the radiator drain petcock at the bottom passenger side of the radiator by turning counterclockwise. Drain approximately 2 gallons of coolant into drain pan. Once flow reduces to a drip, close the petcock by turning clockwise hand-tight.
2. 2

   Access thermostat housing
   The thermostat housing is located on the front of the engine block, below the throttle body on the passenger side. Remove the air intake tube from the throttle body to the air filter box for improved access. Disconnect the electrical connector from the coolant temperature sensor on the thermostat housing by pressing the release tab and pulling straight out.
3. 3

   Disconnect coolant hoses
   Locate the upper radiator hose and heater hose connections at the thermostat housing. Use pliers to compress and slide the spring-style hose clamps away from the housing. Twist each hose to break the seal, then pull hoses off the housing. Be prepared for residual coolant spillage.
   ⚠Coolant will drain from hoses. Have shop towels and drain pan positioned to catch spillage.
4. 4

   Remove thermostat housing bolts
   Remove the three 8mm bolts securing the thermostat housing to the engine block using a socket and ratchet. Keep track of bolt locations as they may be different lengths. Carefully pull the housing away from the engine block.
   Torque spec

   Thermostat Housing Bolts15 Nm (11 lb-ft)
5. 5

   Remove old thermostat
   Extract the old thermostat from the housing or engine block (location varies by production date). Note the orientation of the thermostat with the spring side facing toward the engine block. Remove and discard the old O-ring or gasket.
6. 6

   Clean mating surfaces
   Using a plastic scraper or gasket removal tool, carefully clean all gasket material and residue from both the thermostat housing and engine block mating surfaces. Ensure surfaces are completely clean and dry. Do not allow debris to fall into the engine coolant passages.
   ⚠Do not use metal scrapers that could gouge aluminum surfaces. Cover open coolant passages with clean shop towels to prevent debris entry.
7. 7

   Install new thermostat
   Install the new O-ring or gasket onto the thermostat or into the housing groove as applicable. Position the new thermostat with the spring side facing toward the engine block, ensuring it seats properly in the recess. The air bleed valve (small hole or valve) should be positioned at the top.
8. 8

   Install thermostat housing
   Position the thermostat housing onto the engine block, ensuring the thermostat remains properly seated. Start all three mounting bolts by hand to ensure proper thread engagement. Tighten bolts in a crisscross pattern to the specified torque.
   Torque spec

   Thermostat Housing Bolts15 Nm (11 lb-ft)
9. 9

   Reconnect coolant hoses
   Push the upper radiator hose and heater hose firmly onto the thermostat housing until they are fully seated. Position the hose clamps over the hose beads and ensure they are properly seated. If using new screw-type clamps, tighten to specification.
10. 10

    Install coolant temperature sensor
    Apply a small amount of thread sealant to the threads of the coolant temperature sensor if it was removed. Thread the sensor into the thermostat housing by hand, then tighten to specification using a socket. Reconnect the electrical connector until it clicks into place.
    ℹ️Use only approved thread sealant. Excessive sealant can contaminate coolant or block sensor port.
    Torque spec

    Coolant Temperature Sensor20 Nm (15 lb-ft)
11. 11

    Refill cooling system
    Pour Motorcraft Orange coolant into the coolant reservoir until it reaches the MAX COLD line. Start the engine and let it idle with the reservoir cap off. As the thermostat opens and coolant circulates, the level will drop - continue adding coolant to maintain proper level. Run engine until cooling fans cycle on and off at least once.
12. 12

    Bleed air from system
    With engine at operating temperature, locate the bleed screw on top of the thermostat housing or nearby coolant passage. Slowly open the bleed screw until coolant flows without air bubbles, then close to specification. Top off coolant reservoir to MAX COLD line and install cap securely.
    ⚠Engine and coolant will be hot. Use caution when opening bleed screw to avoid burns.

Reassembly

1. Reinstall air intake tube and secure all clamps
2. Reinstall engine cover by aligning rear tabs first, then pressing down on front clips until seated
3. Verify all electrical connectors are fully engaged
4. Check that no tools or materials were left in engine bay

Verification

• Start engine and verify no coolant leaks at thermostat housing, hoses, or sensor
• Allow engine to reach operating temperature and confirm cooling fans activate normally
• Check that heater produces hot air when set to maximum temperature
• Monitor coolant level in reservoir - should remain stable between MIN and MAX marks
• Verify engine temperature gauge reads in normal range (approximately halfway)
• After initial test drive, recheck coolant level when engine is cold and top off if needed

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