Thermostat

Replace the thermostat on a 2015-2020 Ford F-150 with 5.0L Coyote V8 engine to restore proper engine temperature regulation.

Warnings

Tools required

Parts

• Thermostat assembly with O-ring × 1 — Use OEM specification
• Coolant (orange pre-diluted) × 1 — Motorcraft 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 ground and engage parking brake
3. Place drain pan under the radiator drain petcock located at the bottom driver side of the radiator
4. Remove the engine cover by pulling upward on the front and rear pull tabs

Procedure

1. 1

   Drain cooling system
   Open the radiator drain petcock at the bottom of the radiator by turning counterclockwise. Allow approximately 2 gallons of coolant to drain into the drain pan. You do not need to drain the entire system, just enough to lower the coolant level below the thermostat housing. Close the petcock when coolant level is below the thermostat.
2. 2

   Access thermostat housing
   The thermostat housing is located on the lower front driver side of the engine block, below the alternator. Identify the thermostat housing where the lower radiator hose connects. You may need to reach down from above or access from underneath the vehicle for better visibility.
3. 3

   Disconnect lower radiator hose
   Locate the spring-type hose clamp securing the lower radiator hose to the thermostat housing outlet. Using pliers or a hose clamp tool, compress the clamp tabs and slide the clamp back along the hose away from the housing. Twist and pull the lower radiator hose off the thermostat housing. Have a rag or drain pan ready as residual coolant will drain out.
4. 4

   Remove coolant bypass hose
   Locate the smaller coolant bypass hose connected to the side of the thermostat housing. Use pliers to compress the spring clamp and slide it back along the hose. Carefully remove the bypass hose from the thermostat housing. Additional coolant will drain, so keep rags or drain pan positioned.
5. 5

   Disconnect coolant temperature sensor
   Locate the coolant temperature sensor (CTS) mounted in the thermostat housing. Press the locking tab on the electrical connector and carefully disconnect the wiring harness from the sensor. If the sensor is being reused, leave it installed in the housing. If replacing, unscrew it counterclockwise using a deep socket.
   ⚠Do not pull on the wiring harness to disconnect. Use only the connector body to avoid damaging the wires.
   Torque spec

   Coolant Temperature Sensor20 Nm (15 lb-ft)
6. 6

   Remove thermostat housing bolts
   Using a 10mm socket, remove the two or three bolts securing the thermostat housing to the engine block. Keep track of bolt locations as they may be different lengths. Carefully pull the thermostat housing away from the engine block. The thermostat may come out with the housing or remain seated in the engine block.
   Torque spec

   Thermostat Housing Bolts15 Nm (11 lb-ft)
7. 7

   Remove old thermostat and clean surfaces
   Remove the old thermostat from the housing or engine block recess. Note the orientation - the spring side faces toward the engine block. Remove and discard the O-ring seal. Using a razor blade or gasket scraper, carefully clean all gasket material and residue from both the engine block mating surface and the thermostat housing mating surface. Spray brake cleaner on both surfaces and wipe completely clean with shop towels. Surfaces must be completely clean and dry for proper seal.
   ⚠Do not gouge or scratch the aluminum mating surfaces. Deep scratches will cause coolant leaks. Use plastic scrapers if available.
8. 8

   Install new thermostat
   Install the new O-ring seal into the groove on the new thermostat or in the engine block recess (depending on design). Lightly lubricate the O-ring with fresh coolant. Install the new thermostat into the engine block recess with the spring side facing INTO the engine block and the bridge or air bleed hole positioned at the top (12 o'clock position). Verify the thermostat seats fully and the O-ring is properly positioned.
9. 9

   Reinstall thermostat housing
   Position the thermostat housing over the thermostat and align the bolt holes with the engine block. If reusing the coolant temperature sensor, ensure it is still properly installed. Install the housing bolts hand-tight, then torque to specification in a criss-cross pattern.
   Torque spec

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

    Reconnect coolant temperature sensor
    If the coolant temperature sensor was removed, apply a thin coat of thread sealant to the sensor threads and install it into the thermostat housing. Torque to specification. Reconnect the electrical connector to the sensor until it clicks into place.
    Torque spec

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

    Reconnect coolant hoses
    Reconnect the coolant bypass hose to the thermostat housing and position the spring clamp over the connection point. Reconnect the lower radiator hose to the thermostat housing outlet, ensuring it is fully seated. Position and secure the spring-type hose clamp in its proper location. Verify both hoses are fully seated and clamps are properly positioned.
12. 12

    Refill cooling system
    Fill the cooling system through the radiator cap opening with Motorcraft Orange pre-diluted coolant. Fill slowly to allow air to escape. Add coolant until it reaches the base of the radiator neck. If equipped with a cooling system bleed screw on the upper radiator hose or thermostat housing, open it while filling to release trapped air. Close the bleed screw when coolant flows out without air bubbles.
    ℹ️Only use Motorcraft Orange coolant or equivalent. Do not mix with other coolant types as this will void warranty and may cause cooling system damage.
13. 13

    Bleed air from cooling system
    Install the radiator cap. Start the engine and allow it to idle with the heater on maximum heat setting. Monitor the temperature gauge - it should rise to normal operating temperature (approximately halfway on the gauge). Listen for the cooling fans to cycle on. As the thermostat opens, the coolant level may drop. After the engine reaches operating temperature and the cooling fans cycle, shut off the engine and allow it to cool for 15 minutes. Recheck coolant level and top off as necessary.

Reassembly

1. Reinstall the engine cover by aligning the grommets and pressing down firmly until it clicks into place
2. Verify all tools and parts have been removed from the engine bay
3. Check underneath the vehicle for any coolant leaks at the thermostat housing and hose connections

Verification

• Start the engine and verify no coolant leaks at the thermostat housing, lower radiator hose, or bypass hose connections
• Allow engine to reach normal operating temperature and confirm the temperature gauge reads in the normal range (approximately 195-220°F)
• Verify the upper radiator hose becomes hot to the touch after the thermostat opens, indicating proper coolant circulation
• Check that the heater produces hot air at idle and during driving
• After the first drive cycle, recheck coolant level when engine is cold and top off if necessary
• Monitor for any coolant puddles under the vehicle over the next few days

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