cooling

Thermostat Housing

for 2017 Honda Civic 1.5L I4 Turbo · FWD

Difficulty

Moderate

Time

1.2 h

Tools

Steps

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This procedure covers removal and replacement of the thermostat housing on the 2016-2021 Honda Civic 1.5L Turbo engine, including coolant drainage, housing removal, gasket replacement, and coolant refill.

Warnings

⚠️Never open the cooling system when the engine is hot. Allow engine to cool completely for at least 2 hours to avoid severe burns from pressurized coolant.

⚠The thermostat housing is located on the engine side near the firewall with limited clearance. Use care when removing bolts to avoid dropping them into the engine bay.

⚠Only use Honda Type 2 (Blue) coolant. Mixing coolant types or using incorrect coolant can cause cooling system damage.

ℹ️The thermostat housing is integrated with the coolant outlet on this engine and is located on the driver's side of the cylinder head near the firewall.

Tools required

10mm socket and ratchetEssential

12mm socket and ratchetEssential

Torque wrench (5-30 Nm range)Essential

Drain pan (minimum 2 gallon capacity)Essential

Pliers or hose clamp toolEssential

Plastic scraper or gasket remover

Shop ragsEssential

FunnelEssential

Wire brush

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Parts

Thermostat housing × 1 — Use OEM specification
Thermostat housing gasket/O-ring × 1 — Use OEM specification
Coolant drain plug washer × 1 — 94109-14000 or equivalent

As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.

Fluids

Honda Type 2 Coolant (Blue) — 6 qt

Preparation

Ensure engine is completely cold (at least 2 hours after last operation)
Park vehicle on level surface and apply parking brake
Place drain pan under radiator drain plug location
Remove engine cover by pulling upward on the cover tabs
Verify you have the correct replacement thermostat housing and gasket/O-ring for the 1.5L Turbo engine

Procedure

1
Drain engine coolant
Locate the radiator drain plug on the driver's side lower corner of the radiator. Place a drain pan underneath and carefully remove the drain plug. Allow coolant to drain completely. Remove the radiator cap to speed drainage.
Torque spec
Coolant Drain Plug15 Nm (11 lb-ft)
2
Access thermostat housing
The thermostat housing is located on the driver's side of the cylinder head near the firewall. Remove the air intake duct if necessary for better access. Identify the two coolant hoses connected to the housing (upper radiator hose and a smaller bypass hose).
3
Disconnect upper radiator hose
Using pliers or hose clamp tool, loosen the hose clamp securing the upper radiator hose to the thermostat housing. Slide the clamp back away from the connection point. Twist the hose gently to break the seal, then pull it off the housing neck. Be prepared for residual coolant spillage.
Torque spec
Coolant Hose Clamps4 Nm (3 lb-ft)
4
Disconnect bypass hose
Locate the smaller coolant bypass hose connected to the lower portion of the thermostat housing. Loosen the hose clamp and slide it back. Twist and remove the hose from the housing. Have a rag ready to catch any remaining coolant.
Torque spec
Coolant Hose Clamps4 Nm (3 lb-ft)
5
Disconnect electrical connector
Locate the coolant temperature sensor electrical connector on the thermostat housing. Press the locking tab and carefully disconnect the electrical connector. Move the wiring harness aside to prevent damage during housing removal.
6
Remove thermostat housing bolts
Remove the two 10mm bolts securing the thermostat housing to the cylinder head. Due to tight clearance near the firewall, use a socket with extension or universal joint. Keep track of bolt locations as they thread into the aluminum cylinder head.
⚠Do not drop bolts into engine bay. Consider using magnetic tools or attaching bolts to a magnetic tray immediately after removal.
Torque spec
Housing Bolts13 Nm (10 lb-ft)
7
Remove thermostat housing
Carefully pull the thermostat housing away from the cylinder head. The housing may be stuck due to the gasket seal. Gently twist and wiggle to break the seal. Remove the old gasket/O-ring from the mating surface on the cylinder head.
8
Clean mating surfaces
Thoroughly clean both the cylinder head mating surface and the new thermostat housing mating surface using a plastic scraper. Remove all old gasket material, dirt, and debris. Do not use metal scrapers on aluminum surfaces. Wipe clean with a lint-free rag. Inspect for cracks or damage.
⚠Ensure mating surfaces are completely clean and dry. Any debris or old gasket material will cause coolant leaks.
9
Install new gasket and housing
Position the new gasket/O-ring onto the new thermostat housing or into the groove on the cylinder head (depending on design). Align the thermostat housing with the mounting holes on the cylinder head. Carefully position the housing ensuring the gasket stays in place.
10
Install and torque housing bolts
Hand-thread both thermostat housing bolts to avoid cross-threading. Tighten bolts evenly in a criss-cross pattern to ensure even gasket compression. Use a torque wrench to tighten bolts to specification.
⚠Do not overtighten bolts. The cylinder head is aluminum and threads can be damaged easily. Use a torque wrench.
Torque spec
Housing Bolts13 Nm (10 lb-ft)
11
Reconnect coolant hoses
Reconnect the bypass hose to the lower connection on the thermostat housing. Slide the hose clamp into position and tighten to specification. Reconnect the upper radiator hose to the housing neck, ensuring it is fully seated. Position and tighten the hose clamp.
Torque spec
Coolant Hose Clamps4 Nm (3 lb-ft)
12
Reconnect electrical connector
Reconnect the coolant temperature sensor electrical connector to the thermostat housing. Ensure the connector clicks into place and the locking tab is fully engaged.
13
Install drain plug and refill coolant
Install a new drain plug washer on the radiator drain plug. Thread the drain plug into the radiator and torque to specification. Using a funnel, fill the cooling system with Honda Type 2 (Blue) coolant through the radiator cap opening until full. Fill the coolant reservoir to the MAX line.
Torque spec
Coolant Drain Plug15 Nm (11 lb-ft)
14
Bleed cooling system
With the radiator cap still off, start the engine and allow it to reach normal operating temperature with the heater on maximum. Watch the coolant level and add coolant as needed as air purges from the system. When the radiator cooling fan cycles on, the thermostat has opened. Allow the engine to run until no more air bubbles appear in the radiator.
⚠Monitor coolant temperature during bleeding. If engine begins to overheat, shut off immediately and allow to cool.
15
Final fill and cap installation
With the engine off and cooled slightly, top off the radiator to the fill neck. Install the radiator cap securely. Check the coolant reservoir level and fill to MAX line if needed. Reinstall the engine cover.

Reassembly

Ensure all hose clamps are properly tightened and positioned
Verify electrical connector is fully seated and locked
Double-check that no tools or rags were left in the engine bay
Reinstall air intake components if removed during access

Verification

Start the engine and visually inspect the thermostat housing area for coolant leaks while engine warms up
Monitor coolant temperature gauge to ensure engine reaches normal operating temperature (thermostat opening properly)
Verify radiator cooling fan cycles on when engine reaches operating temperature
After test drive, recheck coolant level when engine is cold and top off if necessary
Inspect again for any coolant leaks around housing gasket and hose connections
Check for proper heater operation inside vehicle cabin