🔧 Thermostat - Replacement

On your Highlander, the thermostat controls coolant flow to help the engine reach (and stay at) the correct temperature. Replacing it involves draining some coolant, removing the thermostat housing (where the lower radiator hose connects), installing a new thermostat/seal, then refilling and bleeding air from the cooling system.

Difficulty Level: Intermediate | Estimated Time: 2-4 hours

---

⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine only; hot coolant can cause severe burns.
• ⚠️ Never open the radiator cap when hot or pressurized.
• ⚠️ Support the vehicle with jack stands; never rely on a jack alone.
• ⚠️ Keep coolant away from kids/pets; dispose of old coolant properly.
• ⚠️ Battery disconnect is not required, but keep tools clear of the radiator fans (they can turn on unexpectedly).

---

🔧 Required Tools

You'll need the following tools for this repair:

• Floor jack (rated 3-ton minimum)
• Jack stands (rated 3-ton minimum)
• Wheel chocks
• Safety glasses
• Nitrile gloves
• Drain pan (at least 10-quart)
• Funnel (spill-free coolant funnel kit) (specialty)
• Trim clip removal tool
• Flat-blade screwdriver
• Pliers
• Hose clamp pliers (specialty)
• 10mm socket
• 12mm socket
• 3/8" drive ratchet
• 3/8" drive extension set
• Torque wrench (3/8" drive, 5–60 Nm range)
• Plastic gasket scraper
• Shop rags

---

🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Engine coolant thermostat - Qty: 1
• Thermostat seal / O-ring - Qty: 1
• Toyota Super Long Life Coolant (pink, premixed 50/50) - Qty: 2 gallons
• Small hose clamps (optional) - Qty: 2

---

📋 Before You Begin

• 🅿️ Park on level ground, set the parking brake, and chock the rear wheels.
• 🧊 Let the engine cool completely (overnight is best).
• 🧰 If you have it, set up a spill-free funnel kit (it helps prevent air pockets; an “air pocket” is trapped air that can cause overheating).
• 🧼 Lay cardboard under the front of the vehicle to catch drips.

---

🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Raise and secure the front of the vehicle

• Use a floor jack (rated 3-ton minimum) to lift at the front center jacking point.
• Place jack stands (rated 3-ton minimum) under the proper front support points and lower the vehicle onto them.
• Keep wheel chocks behind the rear wheels.

Step 2: Remove the lower engine cover (undertray)

• Put on safety glasses and nitrile gloves.
• Use a trim clip removal tool and flat-blade screwdriver to remove the plastic clips.
• Use a 10mm socket with a 3/8" drive ratchet to remove any undertray bolts, then remove the cover.

Step 3: Drain coolant (enough to get below thermostat level)

• Place a drain pan (at least 10-quart) under the radiator drain area.
• Slowly loosen the radiator cap (engine cold) to relieve any residual pressure.
• Open the radiator drain using pliers or by hand (varies by drain style) and drain coolant.
• Tip: Drain 1–2 gallons to reduce spills.

Step 4: Access the thermostat housing

• From the lower front area, locate the thermostat housing where the lower radiator hose connects to the engine-side coolant inlet.
• Use shop rags to wipe the area clean so dirt doesn’t fall inside.

Step 5: Remove the lower radiator hose from the thermostat housing

• Use hose clamp pliers (specialty) to compress the spring clamp and slide it back on the hose.
• Twist the hose gently to break it free, then pull it off. Use pliers carefully if needed.
• Catch any remaining coolant with the drain pan (at least 10-quart).

Step 6: Remove the thermostat housing

• Use a 10mm socket with a 3/8" drive ratchet and 3/8" drive extension set to remove the thermostat housing bolts.
• Pull the housing straight off. If it’s stuck, tap lightly by hand—do not pry hard on plastic sealing surfaces.

Step 7: Replace the thermostat and seal

• Note the thermostat orientation before removal (the jiggle/bleed valve, if equipped, should be installed in the same position as removed).
• Remove the old thermostat and old thermostat seal / O-ring.
• Clean the mating surfaces using a plastic gasket scraper and shop rags. Do not gouge the aluminum.
• Install the new thermostat and new seal exactly as the old one sat.
• Tip: A tiny coolant film helps O-ring seating.

Step 8: Reinstall the thermostat housing

• Reinstall the housing and start bolts by hand to avoid cross-threading.
• Tighten bolts evenly using a 10mm socket.
• Final tighten using a torque wrench (3/8" drive, 5–60 Nm range): Torque to 10 Nm (89 in-lbs).

Step 9: Reconnect the lower radiator hose

• Push the hose fully onto the housing until it seats.
• Use hose clamp pliers (specialty) to move the clamp back into its original position.

Step 10: Refill coolant and bleed air

• Install the funnel (spill-free coolant funnel kit) (specialty) at the radiator fill neck.
• Pour in Toyota Super Long Life Coolant (pink, premixed 50/50) slowly.
• Start the engine and set the HVAC to full hot (this helps move coolant through the heater core).
• Let the engine idle while topping off as the level drops. Watch for bubbles to slow down.
• When the cooling fan cycles and the heater blows hot, shut the engine off and let it cool.
• Top off radiator and overflow reservoir using a funnel.

Step 11: Reinstall undertray and lower the vehicle

• Reinstall the undertray using the 10mm socket, trim clip removal tool, and flat-blade screwdriver.
• Use the floor jack (rated 3-ton minimum) to lift slightly, remove jack stands (rated 3-ton minimum), and lower the vehicle.

---

✅ After Repair

• 🔍 Check for leaks around the thermostat housing and the lower hose with the engine running.
• 🌡️ Test drive 10–15 minutes while watching the temperature gauge.
• 🧊 After the engine fully cools, recheck the radiator and overflow reservoir level and top off if needed.
• 🧾 If you had overheating before, confirm the heater output is strong at idle (weak heat can mean trapped air).

---

💰 DIY vs Shop Cost

Shop Cost: $450-$850 (parts + labor)

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

You Save: $310-$790 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 2-4 hours.

---

🎯 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.