🔧 BRZ - Thermostat Replacement

The thermostat controls coolant flow to keep your BRZ at the correct operating temperature. Replacing it usually means draining some coolant, removing the thermostat housing at the lower radiator hose, installing the new thermostat with a new seal, then refilling and bleeding air from the cooling system.

Difficulty Level: Intermediate | Estimated Time: 1.5-3.0 hours

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⚠️ Safety & Precautions

• 🧯 Never open the cooling system when hot; coolant can spray and burn.
• 🧊 Let the engine cool fully (ideally overnight) before starting.
• 🧍 Use jack stands on solid points; never rely on a floor jack alone.
• 🧪 Capture coolant in a drain pan and dispose of it properly (coolant is toxic).
• 🔋 Battery disconnect is not required for this repair.

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🔧 Required Tools

You'll need the following tools for this repair:

• Floor jack (rated 2-ton minimum)
• Jack stands (rated 2-ton minimum)
• Wheel chocks
• Safety glasses
• Nitrile gloves
• Drain pan (at least 10-quart)
• Funnel with spill-free radiator neck adapter kit (specialty)
• 10mm socket
• 12mm socket
• 3/8" ratchet
• 3" extension
• Torque wrench (3/8", 5–50 Nm range)
• Hose clamp pliers (specialty)
• Trim clip removal tool
• Flathead screwdriver
• Shop rags

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Engine thermostat - Qty: 1
• Thermostat seal / O-ring - Qty: 1
• Subaru-approved coolant (Super Coolant compatible, premixed 50/50) - Qty: 2 gallons
• Hose clamp (optional, if original is weak/damaged) - Qty: 1

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📋 Before You Begin

• Park on level ground, set the parking brake, and place wheel chocks behind the rear tires.
• Let the engine cool completely and confirm the upper radiator hose feels cool.
• Set the cabin HVAC to full HOT (this helps coolant circulate through the heater core during bleeding).
• Plan your lift points: front center jack point, then support with jack stands at the front pinch welds.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Raise the front of the BRZ

• Use a floor jack (rated 2-ton minimum) to lift the front, then set the car onto jack stands (rated 2-ton minimum).
• Place wheel chocks at the rear wheels.

Step 2: Remove the lower engine undercover (splash shield)

• Use a trim clip removal tool to pop out the plastic clips.
• Use a 10mm socket with a 3/8" ratchet to remove any bolts holding the undercover.
• Set the clips/bolts aside in a small pile so nothing gets lost.

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

• Position a drain pan (at least 10-quart) under the radiator drain area.
• Slowly loosen the radiator cap using a shop rag (only if the engine is fully cool).
• Open the radiator drain cock (drain valve) and let coolant flow into the drain pan.
• Stop once the lower hose is emptying.

Step 4: Locate the thermostat housing at the lower radiator hose

• From underneath, find the lower radiator hose where it attaches to the engine (thermostat housing area).
• Wipe dirt away using shop rags so debris doesn’t fall into the housing.

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

• Use hose clamp pliers (specialty) to compress the clamp and slide it back on the hose.
• Twist the hose gently by hand to break it loose, then pull it off. If needed, carefully assist with a flathead screwdriver at the edge.
• Catch remaining coolant in the drain pan (at least 10-quart).
• Don’t gouge the hose sealing surface.

Step 6: Remove the thermostat housing/cover

• Use a 10mm socket (and a 3" extension if needed) with a 3/8" ratchet to remove the thermostat housing bolts.
• Pull the cover off and note how the thermostat sits in the housing before removing it.

Step 7: Install the new thermostat and new seal

• Remove the old thermostat and old seal/O-ring, then clean the mating surfaces using shop rags.
• Install the new seal/O-ring onto the new thermostat (or into the groove, depending on design).
• Install the new thermostat in the same orientation as the original.

Step 8: Reinstall the thermostat housing/cover

• Start the bolts by hand to avoid cross-threading.
• Use a torque wrench (3/8", 5–50 Nm range) to tighten the housing bolts: Torque to 10 Nm (7.4 ft-lbs).

Step 9: Reinstall the lower radiator hose

• Push the hose fully onto the thermostat outlet until it bottoms out.
• Use hose clamp pliers (specialty) to position the clamp back in its original spot.

Step 10: Refill coolant and bleed air from the system

• Install a funnel with spill-free radiator neck adapter kit (specialty) at the radiator fill neck.
• Slowly pour in Subaru-approved coolant (Super Coolant compatible, premixed 50/50) using the funnel until it stays near the top.
• Start the engine and let it idle with the funnel installed.
• Set HVAC to HOT and low fan; watch for air bubbles purging into the funnel.
• As the thermostat opens, the coolant level may drop; add coolant as needed.
• Let the engine reach normal temp and wait for radiator fans to cycle at least once.
• Shut the engine off, let it cool, then remove the funnel and install the radiator cap.

Step 11: Reinstall the splash shield and lower the car

• Reinstall the undercover using the 10mm socket and trim clip removal tool.
• Lower the car safely using the floor jack (rated 2-ton minimum).

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✅ After Repair

• 🔍 With the engine running, check for leaks at the thermostat housing and lower hose connection.
• 🌡️ Test drive 10–15 minutes, then verify the temperature gauge stays normal.
• 🧊 After a full cool-down, recheck the coolant reservoir level and top off if needed.
• 🧾 If you notice overheating or no cabin heat, there’s likely trapped air—repeat the bleed process.

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💰 DIY vs Shop Cost

Shop Cost: $250-$450 (parts + labor)

DIY Cost: $40-$120 (parts only)

You Save: $130-$410 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.5-3.0 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.