Thermostat Housing

This procedure covers the removal and replacement of the thermostat housing assembly on the 3.5L EcoBoost V6 engine, including coolant draining, housing removal, and refilling the cooling system.

Warnings

Tools required

Parts

• Thermostat housing assembly × 1 — Use OEM Ford specification
• Thermostat housing gasket/O-ring kit × 1 — Included with housing or separate
• Engine coolant × 1 — Motorcraft Orange Coolant

Fluids

• Motorcraft Orange Coolant — 2.5 qt

Preparation

1. Ensure engine is completely cold to the touch
2. Park vehicle on level ground and engage parking brake
3. Disconnect negative battery cable to prevent cooling fan activation
4. Remove engine cover by pulling upward on front edge then lifting off
5. Place drain pan beneath radiator drain plug location

Procedure

1. 1

   Drain cooling system
   Locate the radiator drain plug on the lower driver side of the radiator. Slowly open the drain plug and allow coolant to drain into the pan. Once flow stops, close the drain plug and torque to specification. Remove the cooling system pressure cap to aid draining if not already removed.
   Torque spec

   Coolant Drain Plug15 Nm (11 lb-ft)
2. 2

   Remove air intake components
   Disconnect the air intake tube from the throttle body by loosening the hose clamp. Remove the complete air filter housing assembly by unclipping the retaining clips and disconnecting any vacuum lines or sensors. Set aside to provide access to the thermostat housing area on the passenger side of the engine.
3. 3

   Disconnect upper radiator hose
   Locate the upper radiator hose connection at the thermostat housing on the front passenger side of the engine. Use pliers to release the spring clamp or loosen the worm-gear clamp. Twist the hose gently to break the seal, then pull it off the housing. Be prepared for residual coolant spillage.
   Torque spec

   Coolant Hose Clamps5 Nm (3 lb-ft)
4. 4

   Disconnect coolant bypass hoses
   Identify the smaller coolant bypass hoses connected to the thermostat housing. There are typically two bypass hoses on the 3.5L EcoBoost. Release the hose clamps and carefully remove each hose from the housing nipples. Label hoses if needed for correct reinstallation.
   Torque spec

   Coolant Hose Clamps5 Nm (3 lb-ft)
5. 5

   Disconnect wiring harness connectors
   Locate the coolant temperature sensor connector on the thermostat housing. Press the release tab and carefully disconnect the electrical connector. Move the wiring harness aside to prevent damage during housing removal.
6. 6

   Remove thermostat housing bolts
   Locate the three or four bolts securing the thermostat housing to the engine block. Use a socket and extension to remove all mounting bolts. Keep bolts organized as they may be different lengths. Note the bolt positions for reassembly.
   Torque spec

   Housing Bolts16 Nm (12 lb-ft)
7. 7

   Remove thermostat housing
   Carefully pull the thermostat housing away from the engine block. It may require gentle twisting or wiggling to break the gasket seal. Remove the old thermostat from the housing if it did not stay in the block. Inspect the thermostat for proper operation or replace with new.
8. 8

   Clean mating surfaces
   Use a plastic gasket scraper to thoroughly clean the thermostat housing mating surface on the engine block. Remove all old gasket material and residue. Clean the back of the new or existing housing as well. Wipe surfaces with a clean shop towel. Do not allow debris to fall into the coolant passages.
9. 9

   Install new thermostat and housing
   Install the new thermostat into the engine block recess with the spring side facing into the engine. Position the new gasket or O-ring onto the housing or block as designed. Carefully align the new thermostat housing to the block, ensuring the thermostat seats properly and gasket stays in position. Hand-thread all mounting bolts before tightening.
10. 10

    Torque housing bolts
    Tighten the thermostat housing bolts in a crisscross pattern to ensure even gasket compression. Use a torque wrench to tighten all bolts to the specified torque value. Verify each bolt is properly seated and torqued.
    Torque spec

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

    Reconnect coolant hoses and wiring
    Reconnect the upper radiator hose to the thermostat housing, ensuring it is fully seated on the nipple. Install and tighten the hose clamp to specification. Reconnect both bypass hoses and secure with clamps to proper torque. Reconnect the coolant temperature sensor electrical connector until it clicks into place.
    Torque spec

    Coolant Hose Clamps5 Nm (3 lb-ft)
12. 12

    Reinstall air intake system
    Reinstall the air filter housing assembly and reconnect all vacuum lines and sensors that were disconnected. Connect the air intake tube to the throttle body and tighten the hose clamp securely. Ensure all components are properly seated and secured.
13. 13

    Refill cooling system
    Using Motorcraft Orange Coolant premixed 50/50 with distilled water, slowly fill the cooling system through the pressure cap opening. Fill until coolant level is visible in the reservoir at the cold fill line. Allow time for air to escape as you fill. Install the pressure cap securely.
14. 14

    Bleed cooling system
    Reconnect the negative battery cable. Start the engine and allow it to reach normal operating temperature with the heater on maximum heat. Monitor coolant level and add coolant as needed as air purges from the system. The cooling fans should cycle on when the thermostat opens. Shut off engine and allow to cool, then recheck coolant level and top off to the cold fill line.

Reassembly

1. Reinstall engine cover by aligning rear tabs first, then pressing down on front clips until they click
2. Double-check all hose clamps are tight and properly positioned
3. Verify no tools or parts were left in the engine bay
4. Clean any coolant residue from engine components and surrounding areas

Verification

• With engine cold, verify coolant level is at the proper cold fill line on the reservoir
• Start engine and verify no coolant leaks from thermostat housing, hoses, or drain plug
• Confirm engine reaches normal operating temperature (approximately 195-220°F) within 5-10 minutes
• Verify cooling fans activate when engine reaches operating temperature
• Check for proper heater operation with hot air flowing from vents
• After first drive cycle, recheck coolant level when cold and top off if necessary
• Scan for any coolant temperature-related diagnostic trouble codes with an OBD-II scanner

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

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