🔧 Crosstrek - Thermostat Replacement

On your Crosstrek, the thermostat controls coolant flow so the engine warms up quickly and then stays at the correct operating temperature. Replacing it involves draining some coolant, removing the thermostat housing, installing the new thermostat with a new seal, then refilling and bleeding air from the cooling system.

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

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⚠️ Safety & Precautions

• ⚠️ Never open the radiator cap on a hot engine; let it cool fully.
• ⚠️ Coolant is toxic—keep it off paint, pets, and kids; clean spills immediately.
• ⚠️ Support the vehicle with jack stands; never rely on a floor jack alone.
• ⚠️ If you disconnect the battery, you may lose radio clock presets.

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🔧 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)
• Shop towels
• 10mm socket
• 3/8" drive ratchet
• 3/8" drive extension set
• Torque wrench (5–25 ft-lbs range)
• Hose clamp pliers
• Trim clip remover
• Flathead screwdriver
• Funnel
• Spill-free coolant funnel kit (specialty)

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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
• Engine coolant (Subaru Super Coolant compatible premix) - Qty: 2 gallons
• Hose clamp (worm-gear or OE-style) - Qty: 1 (optional, if original is weak)

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📋 Before You Begin

• Park on level ground, set the parking brake, and place wheel chocks behind the rear wheels.
• Let the engine cool completely (ideally overnight).
• Set the cabin heat to HOT (this helps coolant flow through the heater core during bleeding).
• If you want extra room near the radiator fans, disconnect the negative battery terminal using a 10mm socket.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Raise the front and remove the lower splash shield

• Use a floor jack (rated 3-ton minimum) to lift the front jacking point, then support with jack stands (rated 3-ton minimum).
• Remove the lower engine splash shield using a trim clip remover and 10mm socket.

Step 2: Drain coolant from the radiator

• Place a drain pan (at least 10-quart) under the radiator drain area.
• Slowly loosen the radiator cap to first detent (pressure release), then remove it fully once no hissing is present.
• Open the radiator drain cock (petcock) using a flathead screwdriver if needed, and let coolant drain.
• Tip: Keep the drain pan centered; coolant streams shift.

Step 3: Access the thermostat housing

• From underneath, locate the lower radiator hose where it meets the thermostat housing at the front lower area of the engine.
• Use hose clamp pliers to slide the hose clamp back on the lower radiator hose.
• Twist the hose gently to break it free, then pull it off the housing (catch remaining coolant in the drain pan).
• Tip: Don’t pry hard—hoses tear easily.

Step 4: Remove the thermostat housing and thermostat

• Remove the thermostat housing bolts using a 10mm socket, 3/8" ratchet, and 3/8" extension.
• Carefully separate the housing; more coolant will spill, so keep the drain pan positioned.
• Remove the thermostat and the old seal/O-ring by hand.
• Wipe the mating surfaces clean using shop towels (no gouging).

Step 5: Install the new thermostat and seal

• Install the new seal/O-ring onto the new thermostat (match the old orientation).
• Set the thermostat into position in the housing/engine seat the same way the old one sat.
• Reinstall the housing and start the bolts by hand to avoid cross-threading.
• Tighten housing bolts evenly with a 10mm socket.
• Torque to 10 N·m (7.4 ft-lbs) using a torque wrench (5–25 ft-lbs range).

Step 6: Reinstall the lower radiator hose

• Push the hose fully onto the thermostat housing.
• Position the clamp back where it was using hose clamp pliers.
• Wipe any spilled coolant using shop towels.

Step 7: Refill coolant

• Close the radiator drain cock by hand (snug only) using a flathead screwdriver if required.
• Fill the radiator slowly with engine coolant (Subaru Super Coolant compatible premix) using a funnel.
• Fill the coolant overflow reservoir to the “FULL” line.

Step 8: Bleed air from the cooling system

• Install a spill-free coolant funnel kit (specialty) on the radiator filler neck and add coolant into the funnel to keep the level above the neck.
• Start the engine and let it idle; keep the cabin heat set to HOT.
• Watch for air bubbles burping into the funnel. Add coolant as needed so it never sucks air.
• When the thermostat opens, you should feel the upper radiator hose get hot and see a stronger flow in the funnel.
• Once bubbles stop and the cooling fans cycle on/off at least once, shut the engine off and let it cool.
• Remove the funnel, top off the radiator, then install the radiator cap.

Step 9: Reinstall splash shield and lower the vehicle

• Reinstall the splash shield using a 10mm socket and trim clip remover.
• Lower the vehicle using the floor jack (rated 3-ton minimum).

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✅ After Repair

• Start the engine and check carefully for leaks around the thermostat housing and lower radiator hose.
• Test drive 10–15 minutes, then recheck the coolant level after it cools completely; top off the overflow reservoir as needed.
• Confirm normal temperature gauge behavior (no overheating, no fluctuating spikes).
• If the heater blows cold at idle, you likely still have air trapped—repeat the bleeding step.

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💰 DIY vs Shop Cost

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

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

You Save: $170-$590 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.5-2.5 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.