🔧 Highlander - Thermostat Replacement

Your Highlander’s thermostat controls engine temperature by opening and closing coolant flow. Replacing it means draining some coolant, removing the thermostat housing, installing the new thermostat and seal, then refilling and bleeding air out so it doesn’t overheat.

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

---

⚠️ Safety & Precautions

• ⚠️ Never open the coolant cap on a hot engine—hot coolant can spray and burn.
• ⚠️ Support the vehicle with jack stands before working underneath.
• ⚠️ Keep coolant off belts and electrical connectors; wipe spills immediately.
• ⚠️ Dispose of old coolant properly—it's toxic to people and pets.

---

🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• Floor jack (rated 3-ton minimum)
• Jack stands (rated 3-ton minimum)
• Wheel chocks
• Drain pan (at least 10-quart)
• Spill-free coolant funnel kit (specialty)
• Metric socket set (8mm, 10mm, 12mm)
• 3/8" ratchet
• 3/8" torque wrench (10-80 Nm range)
• Extension set (3" and 6")
• Pliers for spring hose clamps
• Trim clip removal tool
• Flat-blade screwdriver
• Shop rags
• Plastic scraper
• Flashlight

---

🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Engine thermostat - Qty: 1
• Thermostat seal / O-ring - Qty: 1
• Toyota Super Long Life Coolant (pink, pre-mixed) - Qty: 2-3 gallons
• Engine undercover fasteners/clips - Qty: 2-6

---

📋 Before You Begin

• Park on level ground, set the parking brake, and place wheel chocks behind the rear tires.
• Let the engine cool completely (overnight is best).
• Set the HVAC to HOT (max temp). This helps coolant circulate through the heater core during bleeding.
• Raise the front of the vehicle with a floor jack and support with jack stands.

---

🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the lower engine undercover

• Use a floor jack (rated 3-ton minimum) and jack stands (rated 3-ton minimum) to safely support the front.
• Use a trim clip removal tool and 10mm socket to remove the undercover fasteners and lower the panel.

Step 2: Relieve any leftover pressure and prep to drain coolant

• Place a drain pan (at least 10-quart) under the radiator drain area.
• Slowly loosen the coolant reservoir cap (or radiator cap if equipped) by hand. Stop if you hear pressure; wait until fully cool.

Step 3: Drain enough coolant to drop the level below the thermostat

• Open the radiator drain cock using a flat-blade screwdriver (turn gently—plastic can crack).
• Drain until the flow slows and the level is below the upper hoses (typically 1–2 gallons).
• Close the drain cock by hand/snug with the flat-blade screwdriver. Don’t overtighten plastic drains.

Step 4: Remove the engine cover and intake ducting (for access)

• Pull up to remove the engine cover by hand.
• Use a flat-blade screwdriver to loosen intake hose clamps.
• Use a 10mm socket to remove any intake duct bolts, then move the ducting aside.

Step 5: Locate the thermostat housing and remove the hose

• Find the thermostat at the engine-side coolant inlet/outlet housing (where a large radiator hose meets the engine).
• Use pliers for spring hose clamps to slide the clamp back on the hose.
• Twist the hose to break it free, then pull it off. Catch spills with shop rags and the drain pan.

Step 6: Remove the thermostat housing

• Use a 10mm socket, 3/8" ratchet, and extension set (3" and 6") to remove the thermostat housing bolts.
• Carefully separate the housing. If it sticks, gently work it loose by hand—avoid prying on sealing surfaces.

Step 7: Replace the thermostat and seal

• Remove the old thermostat and old seal/O-ring by hand.
• Clean the mating surfaces using a plastic scraper and shop rags. Do not gouge the metal.
• Install the new seal/O-ring and new thermostat.
• Position the thermostat’s jiggle valve (a small air-bleed pin/valve) at the top, if equipped.

Step 8: Reinstall the thermostat housing

• Reinstall the housing and start bolts by hand (prevents cross-threading).
• Tighten bolts evenly using a 10mm socket.
• Final tighten with a 3/8" torque wrench (10-80 Nm range): Torque to 10 Nm (89 in-lbs).

Step 9: Reconnect the hose and reassemble removed parts

• Reinstall the coolant hose and move the clamp back using pliers for spring hose clamps.
• Reinstall the intake ducting using a 10mm socket and tighten clamps with a flat-blade screwdriver.
• Reinstall the engine cover by pressing it into place.
• Reinstall the lower undercover using a trim clip removal tool and 10mm socket.

Step 10: Refill and bleed the cooling system

• Install a spill-free coolant funnel kit (specialty) at the fill point.
• Slowly add Toyota Super Long Life Coolant (pink, pre-mixed) until full.
• Start the engine and let it idle. Keep the heater set to HOT.
• Watch for air bubbles in the funnel; add coolant as the level drops.
• As the engine warms up, carefully squeeze the upper radiator hose by hand (with nitrile gloves) to help push air out.
• When bubbles stop and warm air blows from the vents, shut the engine off and let it cool fully.
• Top off coolant to the correct mark in the reservoir.

---

✅ After Repair

• Check for leaks around the thermostat housing and hose connection with a flashlight.
• Test drive 10–15 minutes, then recheck the coolant level after a full cool-down.
• Verify the temperature gauge stays normal and the cabin heater is hot.
• If you ever see overheating, shut it down and re-bleed—air pockets can cause spikes.

---

💰 DIY vs Shop Cost

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

DIY Cost: $60-$180 (parts only)

You Save: $270-$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.