Replace the thermostat and housing gasket on a 2011-2014 Ford F-150 3.5L EcoBoost engine to restore proper coolant temperature regulation.

Warnings

Tools required

Parts

• Thermostat assembly × 1 — Motorcraft RT-1258 or equivalent
• Thermostat housing gasket/O-ring × 1 — Usually included with thermostat
• Motorcraft Orange Coolant (premixed) × 1 — VC-3DIL-B

Fluids

• Motorcraft Orange Coolant — 2 qt

Preparation

1. Ensure engine is completely cold to the touch before beginning work
2. Park vehicle on level surface and engage parking brake
3. Disconnect negative battery cable to prevent accidental fan activation
4. Remove engine cover by pulling upward on cover clips
5. Place drain pan under thermostat housing area on driver side of engine
6. Locate the coolant bleed screw on top of the thermostat housing

Procedure

1. 1

   Drain coolant from thermostat area
   Slowly open the bleed screw on top of the thermostat housing approximately 2-3 turns to relieve any residual pressure, then fully remove it. Allow coolant to drain into the pan. You do not need to drain the entire cooling system, just the area around the thermostat housing. Expect approximately 1-2 quarts to drain.
2. 2

   Disconnect upper radiator hose
   Locate the upper radiator hose connection at the thermostat housing. Use pliers to compress and slide the hose clamp back approximately 2 inches away from the housing connection. Twist the hose gently while pulling to break the seal, then remove the hose from the thermostat housing. Be prepared for additional coolant to drain.
3. 3

   Remove coolant temperature sensor (if equipped on housing)
   If your thermostat housing has a coolant temperature sensor installed directly in it, carefully disconnect the electrical connector by pressing the release tab. Use a deep socket or wrench to unscrew the sensor. Keep the sensor clean and protected for reinstallation.
   ⚠The coolant temperature sensor is fragile. Do not drop it or allow debris to contact the sensing element.
   Torque spec

   Coolant Temperature Sensor20 Nm (15 lb-ft)
4. 4

   Remove thermostat housing bolts
   Locate the three bolts securing the thermostat housing to the engine block. These are typically 8mm bolts. Remove all bolts completely and set aside. On the 3.5L EcoBoost, the housing is on the front of the engine and may be partially obscured by charge air cooler piping.
   Torque spec

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

   Remove thermostat housing and thermostat
   Carefully pull the thermostat housing away from the engine block. The thermostat will either be seated in the housing or remain in the engine block. Remove the thermostat and note its orientation - the spring side faces into the engine block, and the pellet/valve side faces outward toward the radiator. Remove and discard the old gasket or O-ring.
   ℹ️Take a photo of the thermostat orientation before removal to ensure correct installation of the new unit.
6. 6

   Clean mating surfaces
   Thoroughly clean both the engine block mating surface and the thermostat housing mating surface using a plastic scraper. Remove all traces of old gasket material, being careful not to gouge the aluminum surfaces. Wipe clean with a shop towel, then spray with brake cleaner and wipe again. Both surfaces must be completely clean and dry for proper seal.
   ⚠Do not use metal scrapers or abrasive pads on aluminum surfaces as this can cause leaks. Use only plastic scrapers or gasket removal tools.
7. 7

   Install new thermostat
   Install the new thermostat into the engine block recess with the spring side facing INTO the engine and the pellet/valve mechanism facing outward. Ensure the thermostat is fully seated and the alignment tab (if present) is properly positioned. The thermostat should sit flush and not rock or tilt.
   ⚠Installing the thermostat backwards will cause immediate overheating. Verify correct orientation before proceeding.
8. 8

   Install new gasket and thermostat housing
   Position the new gasket or O-ring onto the thermostat housing or into the groove on the engine block (depending on design). Carefully align the thermostat housing over the thermostat and onto the engine block, ensuring the gasket remains properly positioned. Hand-thread all three housing bolts to prevent cross-threading.
   ⚠Start all bolts by hand first. If any bolt does not thread easily, stop and check for cross-threading or misalignment.
   Torque spec

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

   Torque thermostat housing bolts
   Using a torque wrench, tighten the thermostat housing bolts in a crisscross pattern to 15.0 Nm (11.0 lb-ft). Start with the center bolt, then alternate to outer bolts. Do not exceed specified torque as the aluminum housing threads can strip easily.
   Torque spec

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

    Reinstall coolant temperature sensor
    If removed, apply a small amount of thread sealant to the sensor threads (do not get sealant on the sensor tip). Thread the coolant temperature sensor into the thermostat housing by hand, then torque to 20.0 Nm (15.0 lb-ft). Reconnect the electrical connector until it clicks.
    Torque spec

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

    Reconnect upper radiator hose
    Push the upper radiator hose firmly onto the thermostat housing nipple until it is fully seated. Slide the hose clamp back into position approximately 1/4 inch from the end of the nipple. If using a new clamp, tighten to 5.0 Nm (3.0 lb-ft).
12. 12

    Refill cooling system
    Leave the bleed screw fully open. Using a funnel at the coolant reservoir (not the radiator cap), slowly add Motorcraft Orange premixed coolant. Fill until coolant begins to flow from the bleed screw opening, indicating air has been purged from the thermostat area. Once coolant flows steadily from bleed screw with no air bubbles, install and torque the bleed screw to 8.0 Nm (6.0 lb-ft). Continue filling the reservoir to the COLD MAX line.
    ℹ️Fill slowly to allow air to escape. Rushing this process will trap air in the system and cause overheating.
13. 13

    Burp cooling system and check for leaks
    Reconnect the negative battery cable. Start the engine and allow it to idle with the heater on maximum temperature and fan on high. Watch the temperature gauge - it should rise to normal operating temperature (approximately halfway). Monitor the thermostat housing area for any coolant leaks. Once the engine reaches operating temperature and the cooling fans cycle on, shut off the engine and allow it to cool for 15 minutes. Recheck coolant level in the reservoir and top off to COLD MAX line if needed.
    ⚠If the temperature gauge rises above normal or warning lights illuminate, shut off the engine immediately and recheck all connections.

Reassembly

1. Reinstall engine cover by pressing down firmly on all mounting points until clips engage
2. Verify all tools have been removed from engine bay
3. Wipe down any coolant residue from engine components and undercarriage

Verification

• Start engine and verify temperature gauge reaches normal operating range within 5-10 minutes of driving
• Confirm no coolant leaks are present at thermostat housing or hose connections
• Verify heater produces hot air at idle and while driving
• Check coolant level after first drive cycle when engine is cold - top off if necessary
• Monitor for any overheating symptoms or temperature fluctuations during the first few drive cycles

More procedures for this vehicle