🔧 Outback - Thermostat Replacement

Replacing the thermostat on your Outback means draining some coolant, removing the lower thermostat housing, swapping in the new thermostat and gasket, then refilling and bleeding the cooling system. The thermostat controls coolant flow to help the engine warm up and stay at the correct operating temperature.

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

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⚠️ Safety & Precautions

• ⚠️ Work only on a fully cold engine. Hot coolant can cause serious burns.
• ⚠️ Wear safety glasses and gloves because coolant is slippery and toxic.
• ⚠️ Keep coolant away from pets and children. Even a small amount can be dangerous.
• ⚠️ Support the Outback securely with jack stands if you raise the front. Never rely on a jack alone.
• ⚠️ Disconnecting the battery 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
• Flat-blade screwdriver
• Drain pan, 2-gallon minimum
• Funnel
• Cooling system spill-free funnel kit (specialty)
• Torque wrench, inch-pound or low-range
• Plastic scraper
• Shop towels
• Floor jack, rated 2-ton minimum
• Jack stands, rated 2-ton minimum
• Nitrile gloves
• Safety glasses

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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 Super Coolant premix or equivalent blue 50/50 coolant - Qty: 1-2 gallons
• Drain plug gasket, if removed from radiator - Qty: 1

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📋 Before You Begin

• 🅿️ Park your Outback on level ground and let the engine cool completely.
• 🧊 Open the hood and verify the upper radiator hose is cool before touching any cooling system parts.
• 🧤 Put on safety glasses and nitrile gloves before draining coolant.
• 🛞 If extra room is needed, raise the front with a floor jack and support it with jack stands.
• 📌 A thermostat is a temperature-controlled valve. It stays closed when cold and opens as the engine warms up.
• 📌 A spill-free funnel is a tall funnel that locks onto the radiator neck or coolant fill point to help remove trapped air.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the Lower Engine Cover

• Use a 10mm socket and 3/8-inch ratchet to remove the fasteners holding the lower engine splash shield.
• Use a flat-blade screwdriver to gently release any plastic clips.
• Set the cover and fasteners aside in order so they go back in the same places.
• Tip: Take a quick photo first.

Step 2: Drain Some Coolant

• Place a 2-gallon drain pan under the radiator drain area.
• Slowly remove the radiator cap only if the engine is fully cold.
• Use a flat-blade screwdriver by hand to open the radiator drain plug if equipped and drain about 1 gallon of coolant.
• If the drain plug is hard to access, use a flat-blade screwdriver to loosen the lower radiator hose clamp and carefully drain coolant from the hose area instead.
• Close the drain plug snugly by hand. Do not overtighten plastic radiator parts.

Step 3: Locate the Thermostat Housing

• Follow the lower radiator hose to where it attaches to the engine.
• The metal outlet where the lower hose connects is the thermostat housing.
• Use shop towels around the area to catch leftover coolant.

Step 4: Remove the Lower Radiator Hose from the Housing

• Use a flat-blade screwdriver to loosen the hose clamp if it is a worm-style clamp.
• If the clamp is spring-style, compress it carefully with the appropriate hand tool from your basic plier set if available.
• Twist the hose gently by hand to break it loose, then pull it off the housing.
• Do not pry hard against the aluminum housing.
• Tip: Twist first, then pull.

Step 5: Remove the Thermostat Housing

• Use a 12mm socket, 3/8-inch ratchet, and 6-inch extension to remove the thermostat housing bolts.
• Pull the housing straight away from the engine.
• Note the thermostat direction before removing it. The spring side faces into the engine.
• Remove the old thermostat and gasket/O-ring by hand.

Step 6: Clean the Sealing Surfaces

• Use a plastic scraper to clean old gasket material or residue from the housing and engine mating surface.
• Wipe the area clean with shop towels.
• Do not use a metal scraper because it can gouge the aluminum surface and cause leaks.

Step 7: 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 in the same position as the old one.
• If the thermostat has a small jiggle valve or bleed pin, position it at the top, near the 12 o’clock position.
• Tip: Correct direction matters.

Step 8: Reinstall the Thermostat Housing

• Place the thermostat housing squarely against the engine by hand.
• Start the bolts by hand to prevent cross-threading.
• Use a 12mm socket, 3/8-inch ratchet, and 6-inch extension to snug the bolts evenly.
• Use a torque wrench to tighten the thermostat housing bolts to Torque to 10 Nm (7 ft-lbs).

Step 9: Reattach the Lower Radiator Hose

• Push the lower radiator hose fully onto the thermostat housing by hand.
• Use a flat-blade screwdriver to tighten the worm-style hose clamp.
• Make sure the clamp sits behind the raised bead on the housing neck.
• Wipe the area dry with shop towels so leaks are easier to spot later.

Step 10: Refill the Cooling System

• Install the cooling system spill-free funnel kit at the radiator fill neck or coolant fill point.
• Use a funnel to add Subaru Super Coolant premix or equivalent blue 50/50 coolant slowly.
• Fill until the coolant level stabilizes in the funnel.
• Add coolant to the overflow reservoir up to the “FULL” mark.

Step 11: Bleed Air from the Cooling System

• Leave the spill-free funnel kit installed and start the engine.
• Set the cabin heater to full hot and the fan to low.
• Let the engine idle while watching the coolant level in the funnel.
• Add coolant as the level drops.
• When the thermostat opens, the upper radiator hose will get hot and coolant may begin flowing visibly.
• Squeeze the upper radiator hose gently by hand while wearing nitrile gloves to help move trapped air.
• Continue until no more large bubbles appear and the heater blows hot air.

Step 12: Reinstall the Cap and Lower Cover

• Turn the engine off and let it cool enough that coolant is not rising in the funnel.
• Remove the spill-free funnel kit and install the radiator cap securely.
• Use a 10mm socket and 3/8-inch ratchet to reinstall the lower engine cover.
• Use a flat-blade screwdriver to reinstall any plastic clips.
• Tighten splash shield bolts snugly; do not overtighten plastic fasteners.

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✅ After Repair

• ✅ Start the engine and let it reach normal operating temperature while watching the temperature gauge.
• ✅ Check under the thermostat housing and lower radiator hose for leaks.
• ✅ Take a short drive, then let the engine cool completely.
• ✅ Recheck the radiator and overflow reservoir levels after the engine is cold.
• ✅ Top off with the same blue 50/50 coolant if needed.
• ✅ Dispose of old coolant properly at a recycling center or auto parts store that accepts used coolant.

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💰 DIY vs Shop Cost

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

DIY Cost: $35-$90 (parts only)

You Save: $185-$330 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1-2 hours.

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🎯 Ready to get started?

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