🔧 Ascent - Thermostat Replacement

Replacing the thermostat fixes overheating, slow warm-up, or weak cabin heat by restoring proper coolant flow control. On your Ascent, you’ll drain coolant, remove the thermostat housing, install the new thermostat and seal, then refill and bleed air from the cooling system.

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

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⚠️ Safety & Precautions

• ⚠️ Work only on a completely cold engine; hot coolant can cause severe burns.
• ⚠️ Coolant is toxic—catch all coolant in a drain pan and dispose properly.
• ⚠️ Keep coolant off belts and electrical connectors; wipe spills immediately.
• ⚠️ Support the vehicle with jack stands if raised; never rely on a jack alone.
• ⚠️ Battery disconnect is not required for this job, but keep tools away from the alternator and positive terminals.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• Drain pan (2-gallon minimum)
• Floor jack (rated 3-ton minimum)
• Jack stands (rated 3-ton minimum)
• Wheel chocks
• Trim clip removal tool
• 10mm socket
• 12mm socket
• Ratchet
• 3" extension
• Torque wrench (inch-pound)
• Torque wrench (3/8" drive)
• Hose clamp pliers (specialty)
• Pliers
• Pick tool set
• Plastic scraper
• Shop towels
• Funnel
• Spill-free coolant funnel kit (specialty)
• Flashlight

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Engine thermostat - Qty: 1
• Thermostat seal - Qty: 1
• Subaru-approved coolant (Super Coolant equivalent, premix) - Qty: 1-2 gallons
• Replacement hose clamps - Qty: 1-2

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📋 Before You Begin

• Park on level ground, set the parking brake, and let the engine cool completely (ideally overnight).
• Set the HVAC temperature to Heat before starting (helps bleeding later).
• Chock the rear wheels with wheel chocks. If you need access underneath, raise the front with a floor jack and support with jack stands.
• Place a drain pan under the radiator area before opening the system.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Drain coolant to below thermostat level

• Remove any lower splash shielding that blocks access using a trim clip removal tool and a 10mm socket with ratchet.
• Position the drain pan under the radiator.
• Slowly loosen the radiator cap (engine cold) to relieve any residual pressure.
• Drain coolant from the radiator drain if accessible; otherwise, you’ll drain when you remove the lower hose in Step 3.

Step 2: Gain access to the thermostat housing

• Use a flashlight to locate the thermostat housing where a large radiator hose connects to the engine.
• Clear working room by moving any clips/looms gently aside by hand; do not pull on wiring.

Step 3: Remove the radiator hose from the thermostat housing

• Use hose clamp pliers (specialty) to compress the spring clamp and slide it back on the hose. (These pliers lock the clamp compressed.)
• Twist the hose by hand to break it loose, then pull it off the housing.
• If it’s stuck, use a pick tool set to gently separate the hose from the neck without gouging the plastic/metal.
• Let coolant drain into the drain pan.

Step 4: Remove the thermostat housing bolts

• Remove the housing bolts using a 12mm socket, ratchet, and 3" extension.
• Keep bolts organized in the order removed.
• Carefully separate the housing; a little coolant spill is normal—use shop towels.

Step 5: Remove the old thermostat and seal

• Pull the thermostat straight out by hand (note its orientation).
• Remove the old seal from the groove or mating surface.
• Use a plastic scraper to clean the mating surfaces.
• Tip: Do not use a metal razor blade.

Step 6: Install the new thermostat and seal

• Install the new seal onto the thermostat or into the housing groove (match the old setup).
• Install the new thermostat in the same orientation as removed.
• Hold it seated while you bring the housing back into place.

Step 7: Reinstall the thermostat housing

• Start all bolts by hand to avoid cross-threading.
• Tighten bolts evenly using a 12mm socket and ratchet until the housing seats.
• Final tighten with a torque wrench (inch-pound): Torque to 10 Nm (89 in-lbs).

Step 8: Reinstall the radiator hose and clamp

• Push the hose fully onto the housing neck until it bottoms out.
• Position the clamp behind the bead/ridge using hose clamp pliers (specialty).
• If the hose end is swollen/cracked, replace the hose rather than forcing it to seal.

Step 9: Reinstall splash shield (if removed)

• Reinstall bolts with a 10mm socket and ratchet.
• Reinstall clips using the trim clip removal tool.

Step 10: Refill and bleed the cooling system

• Install the spill-free coolant funnel kit (specialty) on the radiator fill neck.
• Slowly add Subaru-approved coolant (premix) using a funnel until the level stays near the top.
• Start the engine and let it idle with HVAC set to hot and fan low.
• Watch for air bubbles in the funnel; add coolant as the level drops.
• When bubbles stop and cabin heat is steady, shut the engine off and let it cool fully.
• After cooling, top off the radiator and overflow reservoir as needed, then reinstall the cap.

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✅ After Repair

• Check carefully for leaks around the thermostat housing and hose connection using a flashlight.
• Take a 10-15 minute drive, then recheck coolant level after a complete cool-down.
• If the temperature gauge rises abnormally, stop driving and re-bleed—air pockets can cause overheating.
• Dispose of used coolant properly at a recycling center or parts store that accepts it.

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💰 DIY vs Shop Cost

Shop Cost: $350-$750 (parts + labor)

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

You Save: $170-$570 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.