🔧 Outback - Thermostat Replacement

The thermostat controls coolant flow to keep your engine at the correct temperature. If it sticks open you can get slow warm-up and poor heat; if it sticks closed you can overheat. On your Outback 3.6R, this job includes draining coolant, swapping the thermostat and seal, then refilling and bleeding air.

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.
• ⚠️ Support the vehicle with jack stands on solid points; never rely on a jack.
• ⚠️ Keep coolant away from pets and kids; it’s toxic and has a sweet smell.
• ⚠️ Let the engine cool fully before draining coolant.
• ⚠️ 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 3-ton minimum)
• Jack stands (rated 3-ton minimum)
• Wheel chocks
• Safety glasses
• Nitrile gloves
• Drain pan (at least 3-gallon)
• 10mm socket
• 3/8" ratchet
• 3/8" torque wrench (5–30 ft-lbs range)
• Flathead screwdriver
• Hose clamp pliers
• Trim clip removal tool
• Pick tool
• Gasket scraper (plastic)
• Shop towels
• Spill-free funnel kit (specialty)

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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
• Subaru-compatible coolant (blue long-life) - Qty: 2 gallons
• Distilled water - Qty: 1 gallon
• Hose clamps - Qty: 1-2

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📋 Before You Begin

• Park on level ground, set the parking brake, and chock the rear wheels.
• Let the engine cool completely (preferably overnight).
• Set the HVAC to HOT during bleeding later so coolant flows through the heater core (the small radiator for cabin heat).
• Plan to capture and properly dispose of old coolant.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Raise the front and remove the lower covers

• Use a floor jack to lift the front, then support with jack stands.
• Use a trim clip removal tool and 10mm socket to remove the lower splash shield/undertray fasteners.

Step 2: Drain the coolant

• Place a drain pan under the radiator drain area.
• Slowly remove the radiator cap (only if the engine is fully cool) by hand with nitrile gloves.
• Open the radiator drain cock using a flathead screwdriver (turn gently) and let coolant drain.
• Tip: Aim the stream with cardboard.

Step 3: Access the thermostat housing

• Locate the lower radiator hose (big hose at the bottom of the radiator) and follow it toward the engine; it leads to the thermostat housing.
• Use hose clamp pliers to compress the clamp and slide it back on the hose.
• Twist the hose to break it free, then pull it off (use a pick tool carefully if it’s stuck—don’t gouge the hose).

Step 4: Remove the thermostat housing cover

• Put shop towels under the area (more coolant will spill).
• Use a 10mm socket and 3/8" ratchet to remove the thermostat housing bolts.
• Remove the housing cover and pull out the thermostat.
• Note the thermostat orientation before removal (important for proper bleeding/flow).

Step 5: Clean the sealing surfaces

• Remove the old gasket/seal with a pick tool.
• Clean the mating surfaces using a plastic gasket scraper and shop towels.
• Do not use heavy force; you want the surface smooth, not gouged.

Step 6: Install the new thermostat and gasket

• Install the new gasket/seal onto the thermostat (or into the housing, depending on design).
• Install the new thermostat in the same orientation as the original.
• Reinstall the housing cover.
• Use a 3/8" torque wrench to tighten housing bolts evenly in steps: Torque to 9.8 Nm (7.2 ft-lbs).
• Tip: Snug evenly to avoid leaks.

Step 7: Reconnect the lower radiator hose

• Slide the hose fully onto the thermostat housing neck by hand.
• Use hose clamp pliers to reposition the clamp back to its original spot.
• If the clamp is weak or deformed, replace it with a new clamp.

Step 8: Refill coolant and bleed air

• Close the radiator drain cock using a flathead screwdriver (snug only).
• Install a spill-free funnel kit (specialty) on the radiator fill neck.
• Fill with Subaru-compatible coolant (blue long-life) (and distilled water if you’re mixing) until the funnel stays about half full.
• Start the engine and let it idle; set HVAC to HOT with the fan on low.
• Watch the funnel level; add coolant as bubbles purge.
• When the radiator fans cycle on/off and the upper radiator hose feels hot, shut the engine off and let it cool, then top off as needed.

Step 9: Reinstall undertray and lower the vehicle

• Use a 10mm socket and trim clip removal tool to reinstall the undertray fasteners.
• Lower the vehicle using the floor jack.

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✅ After Repair

• With the engine fully warmed up, check for leaks around the thermostat housing and lower hose.
• Verify the cabin heat is strong and steady (a sign most air is out).
• After your first drive and a full cool-down, recheck the radiator level and the overflow reservoir; top off if needed.
• If the temperature gauge fluctuates or you hear gurgling, there’s likely trapped air—repeat the bleed process.

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💰 DIY vs Shop Cost

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

DIY Cost: $60-$160 (parts only)

You Save: $190-$590 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.