Thermostat Housing

This procedure covers removal and replacement of the thermostat housing on the 3.5L EcoBoost V6 engine, including coolant drain, housing removal, gasket replacement, and system refill.

Warnings

Tools required

Parts

• Thermostat housing gasket × 1 — Use OEM Ford specification
• Thermostat (if required) × 1 — Use OEM Ford specification
• O-ring seal (if applicable to housing design) × 1 — Use OEM Ford 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 surface and engage parking brake
3. Open hood and secure with hood prop
4. Remove engine cover by pulling upward on retaining clips
5. Place wheel chocks behind rear wheels
6. Locate thermostat housing on front of engine near upper radiator hose connection

Procedure

1. 1

   Relieve cooling system pressure
   Slowly rotate the radiator cap counterclockwise to the first stop to release any residual pressure. Wait for any hissing to stop, then remove cap completely. Place cap in clean area for reinstallation.
2. 2

   Drain engine coolant
   Position drain pan under radiator drain petcock located at lower driver side of radiator. Open drain petcock by turning counterclockwise and allow coolant to drain into pan. If equipped with coolant drain plug on engine block, remove it as well to ensure complete drainage from engine side. Collect and properly dispose of old coolant according to local regulations.
   Torque spec

   Drain Petcock8 Nm (6 lb-ft)

   Coolant Drain Plug15 Nm (11 lb-ft)
3. 3

   Disconnect upper radiator hose
   Locate upper radiator hose connection at thermostat housing. Use hose clamp pliers or flat-blade screwdriver to release hose clamp and slide it back along the hose away from connection point. Twist hose gently to break seal, then pull hose off thermostat housing outlet. Allow any remaining coolant to drain into pan.
   Torque spec

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

   Disconnect coolant hoses from housing
   Identify all coolant hoses connected to the thermostat housing (typically 2-3 hoses including bypass hoses). Release each hose clamp and slide back along hose. Label each hose position with tape or take photo for reference during reassembly. Remove hoses from housing and plug openings with clean shop towels to prevent debris entry.
   Torque spec

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

   Disconnect electrical connectors
   If equipped, disconnect the coolant temperature sensor electrical connector from the thermostat housing. Press the locking tab and pull connector straight out. Do not pull on wires. Move wiring harness aside to provide access to housing bolts.
6. 6

   Remove thermostat housing bolts
   Using 8mm or 10mm socket (verify size for your specific housing), remove the thermostat housing mounting bolts. There are typically 2-3 bolts securing the housing to the engine block or timing cover. Remove bolts in reverse pattern from center outward. Keep bolts organized for reinstallation.
   ℹ️If bolts are difficult to remove, apply penetrating oil and wait 10 minutes before attempting again.
   Torque spec

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

   Remove thermostat housing assembly
   Carefully pull thermostat housing away from engine block. It may be stuck due to old gasket material. Gently pry with plastic scraper if needed, being careful not to damage sealing surfaces. Once removed, extract thermostat from housing or block (depending on design) and inspect for proper operation. Note orientation of thermostat for reinstallation.
8. 8

   Clean mating surfaces
   Use plastic gasket scraper to remove all old gasket material from both the thermostat housing and engine block mating surfaces. Clean surfaces thoroughly with clean shop towel. Inspect both surfaces for damage, warping, or cracks. Both surfaces must be completely clean and dry for proper seal. Do not use metal scrapers that could gouge aluminum surfaces.
   ⚠Do not use abrasive materials or metal scrapers on aluminum surfaces. This can cause leaks.
9. 9

   Install new gasket and thermostat
   Place new thermostat into housing or block recess (depending on design) with spring side facing into engine and air bleed valve positioned at top (usually 12 o'clock position). Install new gasket onto housing, ensuring it seats properly in gasket groove. If using O-ring style seal, lightly lubricate with clean coolant before installation.
10. 10

    Install thermostat housing
    Position thermostat housing onto engine block, carefully aligning with dowel pins if equipped. Ensure gasket remains properly seated. Hand-thread all housing bolts to ensure proper alignment before tightening any bolt. Tighten bolts in a criss-cross pattern starting from center bolt outward to specification using torque wrench.
    Torque spec

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

    Reconnect coolant hoses and electrical connections
    Reconnect all coolant hoses to thermostat housing in correct positions as noted during removal. Slide hose clamps into position over hose connections and tighten to specification. Ensure hoses are fully seated on fittings. Reconnect coolant temperature sensor electrical connector until it clicks into place.
    Torque spec

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

    Close drain and refill cooling system
    Close radiator drain petcock by turning clockwise to specification. If engine block drain plug was removed, reinstall with new seal washer and torque to specification. Slowly fill cooling system through radiator or overflow tank with Motorcraft Orange coolant premixed 50/50 with distilled water. Fill until coolant reaches radiator neck. Allow time for coolant to settle and air to escape.
    ℹ️Fill slowly to minimize air pocket formation. Total system capacity is 13 quarts but you may only need 2 quarts to replace what was drained.
    Torque spec

    Drain Petcock8 Nm (6 lb-ft)

    Coolant Drain Plug15 Nm (11 lb-ft)
13. 13

    Bleed cooling system
    With radiator cap still off, start engine and allow it to warm up to operating temperature. Monitor coolant level and add coolant as level drops while air purges from system. Run heater at maximum temperature to circulate coolant through heater core. When thermostat opens (approximately 180-195°F), you will see coolant circulation increase in radiator. Continue running until cooling fans cycle on and off at least once.
14. 14

    Final fill and pressure test
    With engine still at operating temperature, top off coolant to proper level in radiator neck. Install radiator cap securely. Check overflow tank and fill to COLD fill line. Allow engine to cool completely, then recheck coolant level and top off if needed. Inspect all connections at thermostat housing for leaks.

Reassembly

1. Reinstall engine cover by aligning clips and pressing down until seated
2. Double-check all hose clamp connections for proper tightness
3. Verify no tools or parts were left in engine compartment
4. Wipe up any spilled coolant from engine and components

Verification

• Start engine and monitor temperature gauge for normal operation (approximately 190-200°F)
• Verify no coolant leaks from thermostat housing or hose connections
• Confirm heater produces hot air when set to maximum temperature
• Check coolant level in overflow tank after engine cools - should be at COLD line
• Verify cooling fans cycle on and off properly as engine reaches operating temperature
• Road test vehicle and monitor for overheating or temperature fluctuations
• Recheck coolant level after 24 hours of operation and top off if necessary

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