This procedure replaces the thermostat on a 2021-2024 Ford F-150 with the 3.5L EcoBoost V6 engine, including coolant drain, housing removal, and system refill with proper bleeding.

Warnings

Tools required

Parts

• Thermostat assembly × 1 — Ford OEM or equivalent 180°F rating
• Thermostat housing gasket/O-ring × 1 — Usually included with thermostat
• Coolant hose clamps (if corroded) × 2 — Worm-drive style, various sizes

Fluids

• Motorcraft Orange Coolant — 3 qt

Preparation

1. Ensure engine is completely cold (minimum 2 hours since last operation)
2. Park vehicle on level ground and engage parking brake
3. Disconnect negative battery terminal to prevent cooling fan activation
4. Remove engine cover by pulling upward on retention clips
5. Place drain pan under radiator drain petcock located at bottom driver side of radiator

Procedure

1. 1

   Drain cooling system
   Open the radiator drain petcock by turning counterclockwise. Allow coolant to drain into pan. If equipped with a coolant drain on the engine block (passenger side), open that as well for more complete drainage. Collect and properly dispose of used coolant according to local regulations.
2. 2

   Remove air intake components
   Disconnect the air intake tube from the throttle body by loosening the hose clamp. Remove the air filter box lid and lift out the air filter element. Unbolt and remove the air filter box housing if additional access is needed. Set components aside in a clean area.
3. 3

   Locate and access thermostat housing
   The thermostat housing is located on the front of the engine block, below and behind the throttle body. It connects to the lower radiator hose and engine coolant outlet. You may need to move wiring harnesses aside for clear access. Do not disconnect electrical connectors unless necessary.
4. 4

   Disconnect coolant hoses
   Using hose clamp pliers or screwdriver, loosen the clamps on the upper and lower coolant hoses connected to the thermostat housing. Slide clamps back away from the housing. Twist hoses gently to break the seal, then pull straight off. Be prepared for residual coolant spillage. If hoses are stuck, use a hose pick tool to separate them carefully without damaging the nipples.
   ⚠Do not pry hoses off with metal tools as this can damage the housing nipples and cause leaks.
5. 5

   Remove thermostat housing bolts
   Locate the thermostat housing mounting bolts (typically 2-3 bolts depending on housing design). Using the appropriate socket, remove all housing bolts in a crisscross pattern to prevent warping. Keep bolts organized for reinstallation.
6. 6

   Remove thermostat housing and old thermostat
   Carefully pull the thermostat housing away from the engine block. The thermostat will either be seated in the housing or in the engine block opening. Note the orientation of the thermostat before removal - the spring side typically faces toward the engine. Remove the old thermostat and set aside.
7. 7

   Clean mating surfaces
   Thoroughly clean all gasket material and debris from both the thermostat housing mating surface and the engine block surface using a plastic scraper. Do not use metal scrapers that could gouge the aluminum surfaces. Wipe surfaces clean with shop towels. Inspect for cracks, warping, or damage that could prevent proper sealing.
   ⚠Any scratches or gouges in the mating surfaces can cause coolant leaks. Ensure surfaces are completely smooth and clean.
   Torque spec

   Thermostat Housing Bolts15 Nm (11 lb-ft)
8. 8

   Install new thermostat
   Install the new thermostat into the engine block recess with the spring side facing into the engine (toward the block). Ensure the thermostat is properly seated in its recess and the air bleed valve (small hole or valve) is positioned at the top/highest point. Install new O-ring or gasket onto the thermostat housing if separate from thermostat.
9. 9

   Install thermostat housing
   Position the thermostat housing over the thermostat, aligning the bolt holes. Install all housing bolts finger-tight first to ensure proper alignment. Then torque the housing bolts in a crisscross pattern to specification to ensure even clamping force and proper seal.
   ⚠Over-tightening can crack the aluminum housing. Use a torque wrench and follow the specified 15 Nm (11 lb-ft) torque value.
   Torque spec

   Thermostat Housing Bolts15 Nm (11 lb-ft)
10. 10

    Reconnect coolant hoses
    Slide coolant hoses back onto the thermostat housing nipples, pushing firmly until fully seated. Position hose clamps over the hose-to-nipple connection area and tighten to specification. Ensure clamps are positioned at least 1/4 inch from the hose end.
11. 11

    Close drain and reinstall components
    Close the radiator drain petcock by turning clockwise and tightening to specification (hand-tight). If engine block drain was opened, close it as well. Reinstall air intake components in reverse order of removal, ensuring all connections are secure.
12. 12

    Refill cooling system
    Locate the cooling system bleed screw on the highest point of the cooling system (typically on the thermostat housing or nearby coolant pipe). Open the bleed screw approximately 2 turns. Slowly fill the cooling system through the degas bottle (coolant reservoir) with a 50/50 mixture of Motorcraft Orange Coolant and distilled water until coolant flows steadily from the bleed screw without bubbles. Close the bleed screw to specification. Continue filling the degas bottle to the COLD MAX line.
    ⚠Fill slowly to prevent air pocket formation. Air pockets can cause inaccurate temperature readings and overheating.
13. 13

    Bleed cooling system
    Reconnect the negative battery terminal. Start the engine and allow it to idle. Turn the heater to maximum temperature and fan speed. Monitor the temperature gauge and watch for coolant circulation. As the engine warms and the thermostat opens (around 180°F), the upper radiator hose should become hot. The cooling fans should cycle on and off. Add coolant to the degas bottle as the level drops during bleeding. Run engine until it reaches full operating temperature and fans cycle at least twice.
14. 14

    Final coolant level adjustment
    With engine at operating temperature, carefully open the bleed screw briefly to release any remaining air, then close to specification. Shut off the engine and allow to cool for 30 minutes. Check coolant level in the degas bottle and add coolant to bring level to the COLD MAX line. Check for any leaks around the thermostat housing and hose connections.

Reassembly

1. Reinstall engine cover by aligning clips and pressing down firmly until secured
2. Double-check that all hose connections are tight and clamps are properly positioned
3. Verify that no tools or shop towels were left in the engine bay
4. Dispose of used coolant properly at a recycling center or automotive shop

Verification

• Start engine and verify no coolant leaks at thermostat housing or hose connections
• Monitor engine temperature gauge during initial test drive - temperature should stabilize around 180-200°F
• Verify heater produces hot air at idle and during driving
• Check coolant level in degas bottle after vehicle cools completely - should be at COLD MAX line
• Monitor for coolant level drops over next few days which could indicate air pockets or leaks
• Verify cooling fans activate properly when engine reaches operating temperature
• After first heat cycle, recheck thermostat housing bolt torque and hose clamp tightness

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