🔧 Thermostat - Replacement

The thermostat on your Highlander controls engine coolant flow. If it sticks open, the engine runs cold; if it sticks closed, the engine can overheat quickly. This job requires draining coolant, removing the thermostat housing, and refilling and bleeding the cooling system carefully.

Difficulty Level: Intermediate | Estimated Time: 2-3 hours

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⚠️ Safety & Precautions

• Work only on a completely cold engine. Hot coolant can cause severe burns.
• Support the vehicle securely if you raise it. Use jack stands, not just a jack.
• Keep coolant away from pets and children. It is toxic.
• Disconnect the negative battery cable if you will be working near the starter or any exposed harnesses.
• Do not remove the radiator cap on a hot engine.
• Use caution around the electric cooling fans; they can start unexpectedly.

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🔧 Required Tools

You'll need the following tools for this repair:

• Ratchet
• 10mm socket
• 12mm socket
• Extension bar
• Pliers
• Flat-blade screwdriver
• Torque wrench
• Drain pan
• Funnel
• Floor jack (rated 3-ton minimum)
• Jack stands
• Safety glasses
• Nitrile gloves
• Shop towels

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Thermostat - Qty: 1
• Thermostat housing gasket / O-ring - Qty: 1
• Engine coolant, Toyota pink SLLC equivalent - Qty: 1-2 gallons

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📋 Before You Begin

• Park on level ground and set the parking brake.
• Let the engine cool completely before opening the cooling system.
• Raise the front of the vehicle only if needed for drain access, and support it with jack stands.
• Have a drain pan ready before opening the radiator drain.
• Use the correct Toyota-spec coolant mix. Do not mix random coolant types.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Drain the coolant

• Place a drain pan under the radiator drain area.
• Use a flat-blade screwdriver to open the radiator drain cock slowly.
• Drain enough coolant to get the level below the thermostat housing.
• Close the drain cock when the coolant stops flowing. Torque to 13 N·m (115 in-lbs) if removed.

Step 2: Remove access parts

• Use a 10mm socket and ratchet to remove the engine cover and any intake ducting that blocks access to the thermostat housing.
• Set the parts aside in order so they go back in the same place.
• Keep clips and bolts organized.

Step 3: Remove the thermostat housing

• Use pliers to move any hose clamp away from the housing.
• Use a 12mm socket, extension bar, and ratchet to remove the thermostat housing bolts.
• Pull the housing away carefully and catch any remaining coolant.
• Remove the old thermostat and gasket / O-ring.

Step 4: Install the new thermostat

• Install the new thermostat in the same orientation as the old one.
• Install the new gasket or O-ring.
• Clean the sealing surfaces with a shop towel. Do not scratch the aluminum housing.
• Reinstall the thermostat housing by hand first.
• Use the torque wrench and 12mm socket to tighten the housing bolts evenly. Torque to 10 N·m (89 in-lbs).
• Snug evenly to avoid leaks.

Step 5: Reinstall removed parts

• Reinstall the intake ducting and engine cover using the 10mm socket.
• Reconnect any clamps or clips you removed.
• Check that nothing is left loose in the engine bay.

Step 6: Refill the cooling system

• Close the radiator drain cock if you opened it.
• Use a funnel to fill the cooling system with Toyota-spec coolant.
• Fill slowly to reduce trapped air.
• If your coolant reservoir was low, top it to the correct mark.

Step 7: Bleed air from the system

• Start the engine with the heater set to hot and the fan on low.
• Let the engine idle and watch the coolant level.
• Add coolant as the level drops.
• When the engine reaches operating temperature, check for warm air from the vents and stable coolant flow.
• Shut the engine off, let it cool, and recheck the coolant level.

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✅ After Repair

• Check for leaks at the thermostat housing and hoses.
• Verify the temperature gauge reaches normal and stays steady.
• Check the coolant reservoir again after a full cool-down cycle.
• Take a short road test and recheck for leaks after the test.

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💰 DIY vs Shop Cost

Shop Cost: $350-$650 (parts + labor)

DIY Cost: $60-$140 (parts only)

You Save: $290-$510 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 2-3 hours.

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🎯 Ready to get started?

HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.