This procedure covers removal and replacement of the thermostat housing assembly on the 2019-2024 Toyota RAV4 2.5L I4 engine, including coolant drain, housing removal, and refill.

Warnings

Tools required

Parts

• Thermostat housing assembly × 1 — Use OEM specification
• Thermostat housing gasket/O-ring × 1 — Usually included with housing
• Radiator drain plug washer × 1 — 90044-38132 or equivalent

Fluids

• Toyota Super Long Life Coolant (Pink) — 2 qt

Preparation

1. Ensure engine is completely cold to the touch (at least 2 hours after last operation)
2. Park vehicle on level ground and engage parking brake
3. Remove engine cover by pulling upward on cover - three clips hold it in place
4. Open hood and support with prop rod if necessary

Procedure

1. 1

   Drain cooling system
   Place drain pan under radiator. Locate coolant drain plug on bottom driver's side of radiator. Slowly loosen drain plug to release pressure, then remove completely with new washer ready for reinstall. Allow coolant to drain completely into pan. If drain plug is difficult to access, you may instead disconnect the lower radiator hose at the radiator.
   Torque spec

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

   Remove air intake components
   Disconnect mass airflow sensor electrical connector by pressing tab and pulling straight off. Loosen hose clamp at throttle body. Remove air intake tube by pulling upward and away from engine bay. Set aside in clean area.
3. 3

   Disconnect upper radiator hose
   Locate upper radiator hose connection at thermostat housing on front of engine. Use hose clamp pliers or flathead screwdriver to loosen spring clamp or worm-gear clamp. Slide clamp back on hose away from housing. Twist hose gently while pulling to break seal, then remove from thermostat housing. Expect residual coolant spillage.
   Torque spec

   Coolant Hose Clamps4 Nm (3 lb-ft)
4. 4

   Disconnect coolant bypass hoses
   Identify smaller coolant bypass hoses connected to thermostat housing. These typically include heater inlet hose and engine bypass hose. Loosen hose clamps and slide back on hoses. Remove each hose from housing, noting orientation and position for reinstallation.
   Torque spec

   Coolant Hose Clamps4 Nm (3 lb-ft)
5. 5

   Remove thermostat housing bolts
   Locate three thermostat housing mounting bolts securing housing to engine block. Using 12mm socket, remove all three bolts in reverse criss-cross pattern. Keep bolts organized as they may be different lengths depending on position.
   ℹ️Note bolt positions - some versions use different length bolts in specific locations
   Torque spec

   Housing Bolts14 Nm (10 lb-ft)
6. 6

   Remove thermostat housing assembly
   Carefully pull thermostat housing away from engine block. Housing may stick due to gasket seal - gently twist and work loose if needed. Remove housing and thermostat as complete assembly. Inspect thermostat operation by checking if valve opens when heated above 82°C (180°F) in water bath if testing old part.
7. 7

   Clean mating surfaces
   Thoroughly clean thermostat housing mating surface on engine block using wire brush or plastic scraper. Remove all old gasket material, corrosion, and debris. Surface must be completely clean and smooth for proper seal. Wipe clean with shop rag. Inspect for cracks or damage.
   ⚠Do not use metal scrapers on aluminum surfaces as gouges will cause coolant leaks
8. 8

   Prepare new thermostat housing
   Verify new thermostat housing includes gasket or O-ring seal. If separate, install new gasket/O-ring onto housing groove ensuring proper seating with no twists or gaps. Lightly coat gasket with coolant for easier installation. Verify thermostat is properly positioned in housing with jiggle valve at top.
9. 9

   Install thermostat housing
   Position new thermostat housing assembly onto engine block, aligning bolt holes carefully. Start all three mounting bolts by hand to ensure proper thread engagement and alignment. Once all bolts are started, tighten in criss-cross pattern to specified torque using torque wrench.
   Torque spec

   Housing Bolts14 Nm (10 lb-ft)
10. 10

    Reconnect coolant hoses
    Reconnect all coolant hoses to thermostat housing in reverse order of removal. Ensure hoses are fully seated onto nipples. Position hose clamps over hose ends and tighten to specification. Verify upper radiator hose, heater hose, and bypass hoses are all properly connected and secured.
    Torque spec

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

    Reinstall air intake components
    Reinstall air intake tube by inserting into throttle body and air box. Tighten hose clamp at throttle body. Reconnect mass airflow sensor electrical connector until it clicks into place. Ensure all connections are secure.
12. 12

    Close drain and refill coolant
    Install radiator drain plug with new washer and tighten to specification. Remove radiator cap. Using funnel, slowly fill cooling system with Toyota Super Long Life Coolant (pink) through radiator and coolant reservoir until level reaches fill line. Fill slowly to minimize air pockets.
    ℹ️System capacity is approximately 10 quarts total but only 2-3 quarts will be needed for refill after this procedure
    Torque spec

    Coolant Drain Plug15 Nm (11 lb-ft)
13. 13

    Bleed cooling system
    Start engine and allow to warm up to operating temperature with radiator cap off. Run heater at maximum temperature. Watch coolant level and add as needed while engine runs - level will drop as air purges from system. Squeeze upper radiator hose several times to help release air bubbles. Once engine reaches operating temperature and thermostat opens, top off coolant to proper level.
    ⚠Keep hands clear of cooling fans which will cycle on automatically when engine reaches temperature
14. 14

    Final check and reinstall engine cover
    With engine at operating temperature, check for leaks around thermostat housing and all hose connections. Verify coolant level is correct in both radiator and overflow reservoir. Install radiator cap. Turn off engine and allow to cool. Recheck coolant level when cold and top off reservoir if needed. Reinstall engine cover by aligning clips and pressing down firmly.

Reassembly

1. Torque all fasteners to specification in criss-cross pattern where applicable
2. Ensure all hose clamps are positioned properly over hose ends, not on smooth housing nipples
3. Double-check that all electrical connectors are fully seated and locked

Verification

• Start engine and verify coolant circulates properly with no leaks at thermostat housing
• Confirm engine reaches normal operating temperature (approximately 195°F) and does not overheat
• Check that upper radiator hose becomes hot after thermostat opens (approximately 3-5 minutes of running)
• Verify heater produces hot air at maximum temperature setting
• After test drive, recheck coolant level when engine is cold and top off if necessary
• Inspect all connections for coolant seepage after 24 hours of normal operation

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