🔧 Thermostat - Replacement

The thermostat on your Sequoia controls engine coolant flow and helps the 5.7L warm up and stay at the correct operating temperature. If it is stuck open or closed, you can get poor heat, overheating, or a check engine light. Replacing it means draining some coolant, swapping the thermostat and seal, then refilling and bleeding the cooling system.

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

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⚠️ Safety & Precautions

• Work on a completely cold engine only; hot coolant can cause severe burns.
• Raise the front safely and support it with jack stands before working underneath.
• Keep coolant away from children and pets; it is toxic.
• Use caution around the fan and belts if the engine is run during final checks.
• No battery disconnect is required for this repair.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 12mm socket
• Ratchet
• 3-inch extension
• Drain pan
• Flat-blade screwdriver
• Pliers
• Torque wrench
• Floor jack (rated 3-ton minimum)
• Jack stands
• Funnel
• Safety glasses
• Mechanic gloves
• Shop rags

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Thermostat - Qty: 1
• Thermostat gasket / seal - Qty: 1
• Toyota Super Long Life Coolant, premixed 50/50 - Qty: 1-2 gallons

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📋 Before You Begin

• Park on level ground and set the parking brake.
• Let the engine cool fully before opening the cooling system.
• Raise the front end and support it with jack stands.
• Place a drain pan under the radiator drain area.
• Keep the heater set to HOT for final bleed.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Drain the coolant

• Use a drain pan and open the radiator drain cock enough to lower the coolant level below the thermostat housing.
• If needed, remove the radiator cap only after the engine is fully cold.
• Drain enough coolant so the thermostat housing can be opened without spilling.

Step 2: Gain access to the thermostat housing

• Use a 10mm socket and 12mm socket to remove any lower engine undercover or splash shield blocking access.
• Remove the intake duct or air inlet pieces if they limit access to the front of the engine.
• Work from underneath and above if needed.

Step 3: Remove the thermostat housing

• Use pliers to release the hose clamp and remove the hose from the thermostat housing.
• Use a 10mm socket and ratchet to remove the thermostat housing bolts.
• Pull the housing straight off and catch any remaining coolant in the drain pan.

Step 4: Replace the thermostat

• Remove the thermostat and old gasket or seal from the housing and mating surface.
• Install the new thermostat in the same orientation as the old one.
• Install the new gasket or seal. Make sure it sits flat and clean.
• Do not reuse a flattened seal.

Step 5: Reinstall the housing

• Position the housing carefully so the gasket stays in place.
• Start both bolts by hand, then tighten evenly with a 10mm socket and torque wrench.
• Torque to 9 N·m (80 in-lbs).
• Reconnect the hose and secure the clamp.

Step 6: Reassemble access parts

• Reinstall any intake ducting or covers you removed.
• Use the 10mm socket and 12mm socket to reinstall the undercovers or splash shield.

Step 7: Refill and bleed the cooling system

• Use a funnel to refill with Toyota Super Long Life Coolant, premixed 50/50.
• Fill the radiator and reservoir to the correct marks.
• Start the engine with the heater set to HOT and let it idle.
• Watch for bubbles as air purges from the system.
• Add coolant as the level drops.

Step 8: Check for leaks and verify operation

• Inspect the thermostat housing, hose connection, and drain cock for leaks.
• Let the engine reach operating temperature and confirm warm air from the heater.
• Recheck the coolant level after the engine cools down.

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✅ After Repair

• Test drive and watch the temperature gauge.
• Check for coolant leaks again after the road test.
• Recheck reservoir level the next morning when cold.
• If the check engine light was on, clear codes and confirm they do not return.

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💰 DIY vs Shop Cost

Shop Cost: $320-$550 (parts + labor)

DIY Cost: $45-$110 (parts only)

You Save: $275-$440 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.