Thermostat Housing

This procedure covers removal and replacement of the thermostat housing on the 2018-2024 Honda Accord 1.5L turbo engine, including coolant drainage, housing removal, and refill.

Warnings

Tools required

Parts

• Thermostat housing assembly × 1 — Use OEM specification
• Thermostat housing gasket/O-ring × 1 — Use OEM specification
• Thermostat (if replacing separately) × 1 — Use OEM specification

Fluids

• Honda Type 2 Coolant (Blue) — 6 qt

Preparation

1. Ensure the engine is completely cold (at least 2 hours after last operation)
2. Park vehicle on level ground and engage parking brake
3. Disconnect the negative battery cable and wait 3 minutes
4. Remove the engine cover by pulling upward on the pull tabs
5. Place drain pan underneath the radiator drain plug

Procedure

1. 1

   Drain engine coolant
   Locate the radiator drain plug at the bottom of the radiator on the driver's side. Slowly loosen the drain plug and allow coolant to drain into the pan. Once drained, retighten the drain plug to specification.
   Torque spec

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

   Remove air intake components
   Disconnect the air intake tube from the turbocharger inlet. Loosen the clamp at the air filter box and remove the intake tube to gain access to the thermostat housing area. Move the tube aside.
3. 3

   Disconnect coolant hoses
   Locate the upper radiator hose and bypass hose connected to the thermostat housing. Use pliers to compress and slide the hose clamps back away from the housing connections. Carefully twist and pull the hoses off the housing. Be prepared for residual coolant spillage.
   ℹ️Mark hose positions with tape if routing is not obvious for reassembly.
4. 4

   Disconnect electrical connector
   Locate the coolant temperature sensor on the thermostat housing. Press the locking tab and disconnect the electrical connector. Move the wiring harness aside to prevent damage.
5. 5

   Remove thermostat housing bolts
   Remove the two 10mm bolts securing the thermostat housing to the engine block. Keep track of bolt locations as they may be different lengths. The housing is located below the turbocharger inlet pipe, so access may be tight.
6. 6

   Remove thermostat housing
   Carefully pull the thermostat housing away from the engine block. You may need to gently twist it to break the gasket seal. Remove the old gasket or O-ring from both the housing and engine block mating surfaces.
   ⚠Do not pry against the housing or block mating surfaces as damage will cause coolant leaks.
7. 7

   Clean mating surfaces
   Use a plastic scraper or wire brush to thoroughly clean all gasket material from both the engine block and housing mating surfaces. Wipe clean with shop towels. Inspect surfaces for damage, cracks, or deep scratches that could prevent proper sealing.
8. 8

   Install new gasket and thermostat
   Install the new O-ring or gasket onto the thermostat housing. If replacing the thermostat separately, ensure it is oriented correctly with the jiggle valve at the top position. The thermostat should sit flush in the housing recess.
   ℹ️Do not use sealant on the gasket unless specifically required by the replacement part instructions.
9. 9

   Install thermostat housing
   Position the thermostat housing onto the engine block, ensuring proper alignment of the bolt holes and gasket. Install both mounting bolts hand-tight first, then torque to specification in a criss-cross pattern.
   Torque spec

   Housing Bolts13 Nm (10 lb-ft)
10. 10

    Reconnect coolant hoses
    Slide the upper radiator hose and bypass hose onto the thermostat housing connections. Ensure each hose is fully seated past the bead on the housing nipple. Position the hose clamps over the hose on the housing connection and tighten to specification.
    Torque spec

    Coolant Hose Clamps4 Nm (3 lb-ft)
11. 11

    Reconnect electrical connector
    Reconnect the coolant temperature sensor electrical connector to the sensor on the thermostat housing. Ensure the connector locks securely with an audible click.
12. 12

    Reinstall air intake components
    Reinstall the air intake tube to the turbocharger inlet and air filter box. Tighten the clamps securely. Ensure no hoses or wiring are pinched by the intake components.
13. 13

    Refill coolant system
    Fill the cooling system with Honda Type 2 (blue) coolant through the radiator cap opening. Fill slowly to allow air to escape. Fill to the MAX line on the coolant reservoir. Install the radiator cap securely.
    ⚠Use only Honda Type 2 coolant. System capacity is approximately 6 quarts but may require less depending on how much was drained.
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. Watch the temperature gauge to ensure it does not overheat. As the thermostat opens, the coolant level may drop. Turn off the engine, allow to cool slightly, and top off coolant as needed. Repeat until the level remains stable.
    ⚠Monitor the temperature gauge closely during the first warm-up cycle. If the gauge approaches the red zone, turn off the engine immediately.

Reassembly

1. Reinstall the engine cover by aligning the clips and pressing firmly until seated
2. Check all hose connections and the thermostat housing for any signs of coolant leaks
3. Verify coolant level is at the MAX line on the reservoir when cold

Verification

• Start the engine and verify no coolant leaks from the thermostat housing or hose connections
• Confirm the engine reaches normal operating temperature (halfway on gauge) within 5-10 minutes
• Verify the upper radiator hose becomes hot after the thermostat opens, indicating proper coolant flow
• Check that the heater produces hot air at idle
• After the first drive cycle, recheck coolant level when cold and top off if necessary
• Scan for diagnostic trouble codes related to coolant temperature sensor or thermostat operation

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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