🔧 Outback - Thermostat Replacement

Replacing the thermostat on your Outback involves draining some engine coolant, removing the thermostat housing at the lower front of the engine, installing the new thermostat, then refilling and bleeding the cooling system. A faulty thermostat can cause overheating, slow warm-up, poor heater performance, or unstable temperature readings.

Difficulty Level: Beginner | Estimated Time: 1.5-2.5 hours

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⚠️ Safety & Precautions

• ⚠️ Work only when the engine is completely cool. Hot coolant can cause serious burns.
• ⚠️ Do not open the radiator cap or coolant reservoir cap while the engine is hot.
• ⚠️ Keep coolant away from pets and children. It is poisonous and often tastes sweet.
• ⚠️ Use jack stands if lifting the front of the vehicle. Never rely on a floor jack alone.
• ⚠️ Battery disconnect is not required for this repair.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 12mm socket
• 3/8-inch ratchet
• 3/8-inch extension 6-inch
• Torque wrench 5-50 Nm
• Flat-blade screwdriver medium
• Pliers medium
• Drain pan 2-gallon minimum
• Coolant funnel spill-free kit
• Plastic trim clip remover
• Floor jack rated 2-ton minimum
• Jack stands rated 2-ton minimum
• Nitrile gloves
• Safety glasses
• Shop towels

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Engine coolant thermostat - Qty: 1
• Thermostat gasket/O-ring - Qty: 1
• Subaru-compatible blue long-life coolant premix - Qty: 1-2 gallons
• Radiator drain plug gasket - Qty: 1

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📋 Before You Begin

• Park your Outback on level ground and set the parking brake.
• Let the engine cool for at least 3-4 hours before opening the cooling system.
• If lifting the front, use a floor jack and support the vehicle securely with jack stands.
• Place a drain pan under the radiator before loosening any drain or hose connection.
• A spill-free funnel is a special funnel that locks onto the radiator neck and helps remove air from the cooling system.
• Use the correct Subaru-compatible coolant. Mixing coolant types can reduce corrosion protection.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Raise and Secure the Front

• Use the floor jack rated 2-ton minimum to lift the front of your Outback only if you need more room underneath.
• Place jack stands rated 2-ton minimum under the proper front support points.
• Put on safety glasses and nitrile gloves.
• Never work under only a jack.

Step 2: Remove the Lower Engine Splash Shield

• Use a plastic trim clip remover to remove the plastic clips from the lower splash shield.
• Use a 10mm socket and 3/8-inch ratchet to remove any 10mm bolts holding the shield.
• Lower the splash shield and set it aside.

Step 3: Remove the Radiator Cap

• Make sure the engine is cold.
• Use your hand with a shop towel over the cap and slowly remove the radiator cap.
• If you hear pressure release, stop and wait longer for the engine to cool.

Step 4: Drain Some Coolant

• Place the drain pan 2-gallon minimum under the radiator drain area.
• Use a flat-blade screwdriver medium or your fingers to carefully open the radiator drain plug.
• Drain about 1 gallon of coolant, or enough so the level is below the thermostat housing.
• Close the drain plug gently. Do not overtighten plastic drain parts.
• If replacing the drain plug gasket, install the new radiator drain plug gasket now.

Step 5: Locate the Thermostat Housing

• Follow the lower radiator hose to the engine. The hose connects to the thermostat housing.
• The thermostat housing is the small metal outlet where the lower radiator hose attaches to the engine.
• Use pliers medium to squeeze the spring clamp if you need to move the lower hose for access.
• A spring clamp is a reusable metal clamp that squeezes the hose tightly.

Step 6: Remove the Thermostat Housing

• Place the drain pan 2-gallon minimum under the thermostat housing because more coolant will spill.
• Use a 12mm socket, 3/8-inch extension 6-inch, and 3/8-inch ratchet to remove the thermostat housing bolts.
• Pull the housing straight away from the engine.
• If the housing sticks, tap it lightly by hand. Do not pry hard against the sealing surface.

Step 7: Remove the Old Thermostat

• Pull the old thermostat and gasket/O-ring out by hand.
• Note the thermostat direction before removing it. The spring side faces into the engine.
• Use shop towels to wipe the thermostat housing and engine sealing surfaces clean.
• Do not scrape deeply or gouge the aluminum surface.

Step 8: Install the New Thermostat

• Install the new engine coolant thermostat with the spring side facing into the engine.
• Install the new thermostat gasket/O-ring evenly around the thermostat.
• If the thermostat has a small jiggle valve or air bleed, position it at the top.
• The jiggle valve is a small loose valve that helps trapped air escape.
• Correct direction prevents overheating.

Step 9: Reinstall the Thermostat Housing

• Position the thermostat housing squarely against the engine.
• Start the bolts by hand to prevent cross-threading.
• Use a 12mm socket, 3/8-inch extension 6-inch, and torque wrench 5-50 Nm to tighten the thermostat housing bolts evenly.
• Torque to 8 Nm (71 in-lbs).
• If you moved the lower radiator hose, use pliers medium to reinstall the spring clamp in its original position.

Step 10: Refill the Cooling System

• Install the coolant funnel spill-free kit onto the radiator filler neck.
• Slowly add Subaru-compatible blue long-life coolant premix until the radiator stays full.
• Fill the overflow reservoir to the FULL mark.
• Squeeze the upper radiator hose by hand several times to help move air bubbles out.

Step 11: Bleed Air From the Cooling System

• Leave the coolant funnel spill-free kit installed and partly filled.
• Start the engine and set the heater to full hot with the fan on low.
• Let the engine idle while watching the coolant level in the funnel.
• Add coolant as the level drops.
• Wait for the radiator fans to cycle on, then off, at least once.
• Watch for steady cabin heat and fewer bubbles in the funnel.
• Do not let the temperature gauge climb into the hot zone.

Step 12: Cap the System and Reinstall the Splash Shield

• Turn the engine off and let it cool until the coolant level settles.
• Use the stopper from the coolant funnel spill-free kit to remove the funnel without spilling.
• Install the radiator cap by hand until fully seated.
• Use a 10mm socket and 3/8-inch ratchet to reinstall the lower splash shield bolts.
• Use the plastic trim clip remover or your fingers to reinstall the plastic clips.

Step 13: Lower the Vehicle

• Use the floor jack rated 2-ton minimum to lift the vehicle slightly off the jack stands.
• Remove the jack stands rated 2-ton minimum.
• Lower your Outback slowly to the ground.

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✅ After Repair

• ✅ Start the engine and check for leaks around the thermostat housing, lower radiator hose, and radiator drain plug.
• ✅ Take a short test drive while watching the temperature gauge.
• ✅ After the engine fully cools, recheck the radiator and overflow reservoir levels.
• ✅ Top off only with Subaru-compatible blue long-life coolant premix.
• ✅ If the heater blows cold at idle or the temperature gauge fluctuates, air may still be trapped and the cooling system should be bled again.
• ✅ Dispose of used coolant properly at a recycling center or repair shop that accepts coolant.

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💰 DIY vs Shop Cost

Shop Cost: $220-$420 (parts + labor)

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

You Save: $175-$310 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.0-1.5 hours.

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🎯 Ready to get started?

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