Thermostat

Replace the thermostat on the 2018-2024 Honda Accord 1.5L turbo engine to restore proper coolant temperature regulation.

Warnings

Tools required

Parts

• Thermostat assembly × 1 — 19301-5AA-A01 or equivalent OEM
• Thermostat housing gasket × 1 — Use OEM specification
• Rubber O-ring seal × 1 — Use OEM specification

Fluids

• Honda Type 2 Coolant (Blue) — 2 qt

Preparation

1. Ensure engine is completely cold to touch
2. Park vehicle on level ground and engage parking brake
3. Remove engine cover by pulling upward on the front edge, then lifting off
4. Place drain pan under radiator drain plug at passenger side lower corner of radiator
5. Open radiator cap slowly to release any residual pressure

Procedure

1. 1

   Drain coolant system
   Open the radiator drain plug located at the bottom passenger side of the radiator. Drain approximately 2 quarts of coolant into the drain pan. Once drained, close the drain plug hand-tight. If reusing coolant, ensure it is clean and free of contamination.
2. 2

   Remove air intake components
   Disconnect the air intake duct from the throttle body by loosening the hose clamp. Remove the air intake tube and air box assembly to improve access to the thermostat housing at the rear of the engine block near the firewall.
3. 3

   Disconnect upper radiator hose
   Locate the upper radiator hose connection at the thermostat housing. Use hose clamp pliers to compress and slide back the spring clamp. Twist the hose gently to break the seal, then pull it off the thermostat housing neck. Be prepared for residual coolant spillage.
   ⚠Do not use excessive force when removing hoses as the plastic housing neck can break easily.
4. 4

   Disconnect coolant bypass hose
   Locate the smaller bypass hose connected to the side of the thermostat housing. Use hose clamp pliers to move the clamp back, then carefully remove the hose from the housing. Position shop towels to catch any coolant drips.
5. 5

   Remove thermostat housing bolts
   Using a 10mm socket with extension, remove the two bolts securing the thermostat housing to the engine block. Access is tight from above; you may need to reach from below or from the passenger side wheel well area. Keep bolts organized for reinstallation.
   Torque spec

   Thermostat Housing Bolts15 Nm (11 lb-ft)
6. 6

   Remove thermostat housing and thermostat
   Carefully pull the thermostat housing away from the engine block. The thermostat will be seated in the engine block bore. Remove the thermostat from the block, noting the orientation with the jiggle valve at the top. Remove and discard the old gasket and O-ring seal.
7. 7

   Clean mating surfaces
   Thoroughly clean both the engine block mating surface and the thermostat housing mating surface using a scraper and shop towels. Remove all traces of old gasket material and ensure surfaces are completely clean and dry. Do not allow debris to fall into coolant passages.
   ⚠Ensure all old gasket material is completely removed. Any residual material will cause coolant leaks.
8. 8

   Install new thermostat
   Install the new rubber O-ring seal into the groove on the thermostat. Insert the new thermostat into the engine block bore with the jiggle valve positioned at the highest point (typically 12 o'clock position). Ensure the thermostat seats fully into the recess.
9. 9

   Install thermostat housing
   Position the new gasket on the thermostat housing mating surface. Carefully align the housing with the engine block, ensuring the gasket stays in position. Start both housing bolts by hand to ensure proper thread engagement. Tighten bolts in a crossing pattern to the specified torque.
   Torque spec

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

    Reconnect coolant hoses
    Reconnect the bypass hose to the thermostat housing and position the hose clamp properly. Reconnect the upper radiator hose, ensuring it is fully seated on the housing neck. Position both clamps over the connection areas and secure them.
11. 11

    Reinstall air intake components
    Reinstall the air box and air intake duct assembly. Connect the intake duct to the throttle body and secure the hose clamp. Ensure all connections are secure and no tools or parts are left in the engine bay.
12. 12

    Refill and bleed cooling system
    Locate the bleed screw on top of the thermostat housing. Open the bleed screw by turning counterclockwise 2-3 turns. Slowly fill the radiator with Honda Type 2 coolant until coolant flows from the bleed screw without air bubbles. Close the bleed screw to specification. Continue filling the radiator to the base of the filler neck. Fill the coolant reservoir to the MAX line. Install the radiator cap.
    ℹ️The bleed screw must be open during filling or air pockets will form in the system causing overheating.
13. 13

    Initial system test
    Start the engine and allow it to reach normal operating temperature with the heater set to maximum heat. Monitor the temperature gauge to ensure it reaches and maintains normal operating range (approximately halfway on the gauge). Check for coolant leaks around the thermostat housing and hose connections.
14. 14

    Final coolant level check
    After the engine has cooled completely (minimum 1 hour), recheck the coolant level in both the radiator and reservoir. Top off as necessary with Honda Type 2 coolant. Check the reservoir level again after the next drive cycle.

Reassembly

1. Reinstall the engine cover by aligning the mounting grommets and pressing down firmly until all clips engage
2. Verify all hose clamps are properly positioned and secure
3. Wipe down any spilled coolant from the engine bay and components

Verification

• Start the engine and verify the temperature gauge reaches normal operating temperature within 5-10 minutes
• Confirm both radiator cooling fans activate when the engine reaches operating temperature
• Check that the heater produces hot air at idle and while driving
• Verify no coolant leaks are present at the thermostat housing or hose connections after a test drive
• Monitor coolant level in the reservoir over the next few days and top off if needed

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