🔧 Outback - Thermostat Replacement

Your Outback’s thermostat controls coolant flow to keep engine temperature stable. Replacing it fixes issues like overheating, slow warm-up, or temperature swings, and it’s also a good time to refresh the coolant if it’s old.

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

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⚠️ Safety & Precautions

• ⚠️ Never open the radiator cap on a hot engine; hot coolant can spray and burn you.
• ⚠️ Support the car with jack stands; never rely on a floor jack alone.
• ⚠️ Coolant is toxic to people and pets; catch every drop and clean spills right away.
• Subaru-specific: Use Subaru-approved coolant (Super Coolant compatible) to protect aluminum components.
• Battery disconnect is not required for this job.

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🔧 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 quarts)
• Socket set with ratchet (3/8")
• 10mm socket
• 6" extension (3/8")
• Torque wrench (3/8")
• Flathead screwdriver
• Hose clamp pliers
• Trim clip removal tool
• Funnel
• Spill-free funnel kit (specialty)
• Shop rags

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Engine thermostat - Qty: 1
• Thermostat gasket / seal - Qty: 1
• Engine coolant (Subaru Super Coolant compatible premix) - Qty: 2-3 gallons
• Lower radiator hose clamp - Qty: 1

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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 fully (radiator hoses should feel cool to the touch).
• Set the heater to full HOT before bleeding later; this helps coolant flow through the heater core.
• A spill-free funnel is a tall funnel that helps burp air.
• A torque wrench tightens bolts to exact force.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Raise and support the front of the car

• Use a floor jack (rated 3-ton minimum) to lift the front at the proper front jacking point.
• Place jack stands (rated 3-ton minimum) under solid support points and lower the car onto them.
• Keep wheel chocks in place.

Step 2: Remove the lower engine cover (undertray)

• Use a trim clip removal tool to remove plastic clips.
• Use a 10mm socket with a ratchet (3/8") to remove any 10mm bolts.
• Set the undertray aside.

Step 3: Drain the coolant

• Place a drain pan (at least 10 quarts) under the radiator drain area.
• Slowly remove the radiator cap to relieve any remaining pressure.
• Open the radiator drain (petcock) and let coolant drain into the pan.
• If the petcock is hard to turn, use a flathead screwdriver gently. Do not force it.
• Keep rags ready for drips.

Step 4: Locate the thermostat housing

• From underneath, follow the lower radiator hose to where it bolts to the front-lower area of the engine.
• The thermostat sits behind that hose connection in the thermostat housing.
• 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 to compress the hose clamp and slide it back on the hose.
• Twist the hose gently to break it loose, then pull it off the housing.
• Catch remaining coolant in the drain pan (at least 10 quarts).

Step 6: Remove the thermostat housing bolts

• Use a 10mm socket, ratchet (3/8"), and 6" extension (3/8") to remove the thermostat housing bolts.
• Pull the housing off carefully; more coolant will spill, so keep the drain pan positioned.
• Note how the thermostat is oriented before removing it.

Step 7: Replace the thermostat and seal

• Remove the old thermostat and old seal by hand. Use shop rags to catch drips.
• Clean the mating surfaces using shop rags only. Do not gouge aluminum.
• Install the new thermostat in the same orientation as the old one.
• Install the new thermostat gasket / seal (make sure it sits flat and is not pinched).

Step 8: Reinstall the thermostat housing

• Reinstall the housing and start the bolts by hand to avoid cross-threading.
• Use a 10mm socket and ratchet (3/8") to snug the bolts evenly.
• Use a torque wrench (3/8") to finish tightening: Torque to 7.5 Nm (5.5 ft-lbs).
• Small bolts strip easily—use the torque wrench.

Step 9: Reattach the lower radiator hose

• Push the hose fully onto the thermostat housing outlet by hand.
• Use hose clamp pliers to position the clamp back in its original spot.
• If the clamp is weak or distorted, replace it with a new lower radiator hose clamp.

Step 10: Refill coolant

• Install a spill-free funnel kit (specialty) or funnel at the radiator fill neck.
• Slowly add engine coolant (Subaru Super Coolant compatible premix) until the radiator stays full.
• Fill the coolant overflow tank to the FULL line.

Step 11: Bleed air from the cooling system

• Start the engine and let it idle with the radiator funnel installed.
• Turn cabin heat to HOT and fan on low.
• As the engine warms up, watch for air bubbles and keep coolant topped up in the funnel.
• Carefully squeeze the upper radiator hose by hand (with nitrile gloves) to help push trapped air out.
• When the thermostat opens, you’ll usually see a noticeable flow change and the radiator hose will get hot.
• Once bubbles stop and heat is steady inside the cabin, shut the engine off and let it cool.

Step 12: Final top-off and reassembly

• After it cools, remove the funnel and install the radiator cap.
• Top off the overflow tank using a funnel if needed.
• Reinstall the undertray using the trim clip removal tool and 10mm socket.
• Raise the car slightly with the floor jack, remove jack stands, and lower the car.

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✅ After Repair

• Warm the engine to normal temp and check for leaks around the thermostat housing and lower hose.
• Verify the heater blows hot and the temperature gauge stays steady.
• After your first drive, let it cool and recheck the overflow tank level; top off if needed.
• Dispose of old coolant properly (do not pour it on the ground).

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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.

Assumption: Stock cooling system and OEM-style thermostat housing on your Outback.