🔧 Fusion - Thermostat Replacement

Replacing the thermostat on your Fusion means draining part of the coolant, removing the thermostat housing, installing the new thermostat/seal, then refilling and bleeding the cooling system. The thermostat controls coolant flow so the engine reaches and holds the correct operating temperature.

Difficulty Level: Intermediate | Estimated Time: 2-3 hours

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⚠️ Safety & Precautions

• ⚠️ Let the engine cool completely before opening the coolant reservoir. Hot coolant can spray out and burn you.
• ⚠️ Your Fusion is a plug-in hybrid. Do not touch orange high-voltage cables, connectors, or hybrid components.
• ⚠️ Keep the vehicle OFF and keep the key/fob away from the vehicle while working.
• ⚠️ Wear safety glasses and gloves. Coolant is toxic and slippery.
• ⚠️ Disconnecting the 12V battery is recommended when working near electrical connectors. Do not disconnect any high-voltage orange connectors.
• ⚠️ Dispose of used coolant properly at a fluid recycling center.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• Drain pan 2-gallon minimum
• Coolant fill funnel kit (specialty)
• Funnel with long neck
• Hose clamp pliers
• Slip-joint pliers 10-inch
• Pick tool 90-degree
• Plastic scraper
• Shop towels
• Flashlight
• Floor jack rated 2-ton minimum
• Jack stands rated 2-ton minimum
• Wheel chocks
• 7mm socket
• 8mm socket
• 10mm socket
• 13mm socket
• Ratchet 3/8-inch drive
• Extension 3/8-inch drive 6-inch
• Torque wrench 3/8-inch drive

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Thermostat - Qty: 1
• Thermostat housing seal or O-ring - Qty: 1
• Ford-approved engine coolant concentrate or premix - Qty: 1 gallon
• Distilled water - Qty: 1 gallon if using concentrate
• Thermostat housing bolts - Qty: 2-3 if corroded or damaged

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📋 Before You Begin

• Park your Fusion on level ground and set the parking brake.
• Place wheel chocks behind the rear wheels.
• Let the engine cool fully. Overnight cooling is best for a first-time DIYer.
• Move the key/fob at least 15 feet away from the vehicle.
• The thermostat housing is the small outlet where a radiator hose connects to the engine. The thermostat sits inside or behind that housing.
• A coolant fill funnel kit is a spill-free funnel that helps remove trapped air from the cooling system.
• Before removing anything, take clear phone photos of hose routing, clamp positions, and connector locations.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Make the Vehicle Safe

• Use safety glasses and nitrile gloves before starting.
• Confirm your Fusion is OFF and completely cool.
• Keep the key/fob away from the vehicle so the hybrid system does not wake up.
• Open the hood and use a flashlight to inspect the thermostat housing area.
• Take photos before removing parts.

Step 2: Disconnect the 12V Battery Negative Cable

• Use a 10mm socket with a 3/8-inch ratchet to loosen the 12V battery negative cable nut.
• Remove the negative cable from the battery terminal and position it so it cannot spring back.
• This helps prevent accidental electrical activation while working near connectors.
• Do not touch or disconnect orange high-voltage connectors.

Step 3: Raise the Front of the Vehicle If Needed

• Use a floor jack rated 2-ton minimum to lift the front of the vehicle at the proper front jacking point if lower access is needed.
• Place jack stands rated 2-ton minimum under the front support points.
• Lower the vehicle gently onto the jack stands.
• Keep wheel chocks behind the rear wheels.
• Never work under a vehicle supported only by a jack.

Step 4: Remove the Lower Splash Shield If Needed

• Use a 7mm socket, 8mm socket, or 10mm socket with a 3/8-inch ratchet to remove the lower splash shield fasteners as equipped.
• Remove the splash shield and set it aside.
• Keep the fasteners organized so they return to their original locations.

Step 5: Relieve Cooling System Pressure

• Place a shop towel over the coolant reservoir cap.
• Slowly turn the cap by hand to release any remaining pressure.
• Remove the cap only when there is no hissing sound.
• If pressure releases, stop and let the engine cool longer.

Step 6: Drain Some Coolant

• Place a drain pan 2-gallon minimum under the radiator drain area or below the lower hose area.
• Use a flat-head screwdriver 1/4-inch if your radiator drain plug uses a slotted head.
• Open the drain slowly and drain enough coolant so the level is below the thermostat housing.
• If the drain plug is difficult to access, keep the drain pan under the thermostat hose and expect some coolant spill when the hose is removed.
• Close the drain plug by hand until snug. Do not overtighten plastic radiator parts.

Step 7: Remove Parts Blocking Access

• Use a 7mm socket, 8mm socket, or 10mm socket with a 3/8-inch ratchet to remove any air duct fasteners blocking the thermostat housing area.
• Use slip-joint pliers 10-inch to release any simple duct clamps if equipped.
• Move only what is needed for access.
• Use a flashlight to confirm you can see the thermostat housing bolts and connected hose.

Step 8: Disconnect the Hose from the Thermostat Housing

• Use hose clamp pliers to squeeze the hose clamp ears.
• Slide the clamp back several inches from the hose end.
• Use slip-joint pliers 10-inch to gently twist the hose to break it loose.
• If the hose is stuck, use a 90-degree pick tool carefully around the hose lip.
• Pull the hose off by hand and aim any spilled coolant into the drain pan.
• Do not pry hard against plastic coolant fittings.

Step 9: Remove the Thermostat Housing

• Use a 10mm socket or 13mm socket with a 3/8-inch ratchet and 6-inch extension to remove the thermostat housing bolts.
• Support the housing by hand as the last bolt comes out.
• Pull the housing straight away from the engine.
• Note the thermostat orientation before removal. The new thermostat must face the same way.
• Thermostat housing bolts are typically small. Keep them clean and organized.

Step 10: Remove the Old Thermostat and Seal

• Remove the thermostat by hand.
• Remove the old seal or O-ring by hand or with a 90-degree pick tool.
• An O-ring is a round rubber seal that prevents coolant leaks.
• Use a plastic scraper to clean old residue from the mating surfaces.
• Do not use a metal scraper because it can gouge the sealing surface.

Step 11: Install the New Thermostat and Seal

• Compare the new thermostat and seal with the old parts.
• Install the new thermostat in the same orientation as the old one.
• Install the new thermostat housing seal or O-ring fully into its groove.
• If the seal uses an O-ring, lightly wet it with clean coolant before installation.
• Do not use gasket sealer unless the replacement part instructions specifically require it.

Step 12: Reinstall the Thermostat Housing

• Position the thermostat housing squarely against the engine by hand.
• Start all housing bolts by hand first to avoid cross-threading.
• Use a 10mm socket or 13mm socket with a 3/8-inch ratchet to snug the bolts evenly.
• Use a 3/8-inch torque wrench to tighten the housing bolts evenly.
• Torque to 10 Nm (89 in-lbs) unless the new housing instructions specify a different value.
• Do not overtighten. The housing can crack.

Step 13: Reconnect the Coolant Hose

• Push the hose fully onto the thermostat housing fitting by hand.
• Use hose clamp pliers to move the clamp back behind the raised bead on the fitting.
• The raised bead is the small lip that helps keep the hose from sliding off.
• Make sure the hose is not twisted or rubbing against sharp edges.

Step 14: Reinstall Removed Access Parts

• Use a 7mm socket, 8mm socket, or 10mm socket with a 3/8-inch ratchet to reinstall any air ducts or brackets removed for access.
• Reconnect any electrical connectors that were moved aside.
• Make sure all wiring is clipped back in its original position.

Step 15: Refill the Cooling System

• Install a coolant fill funnel kit onto the coolant reservoir.
• Use a funnel with long neck if a spill-free kit is not available.
• Slowly add Ford-approved coolant until the level reaches the correct mark.
• If using concentrate, premix it with distilled water before pouring it into the vehicle.
• Do not use tap water.

Step 16: Reconnect the 12V Battery

• Install the negative cable onto the 12V battery terminal by hand.
• Use a 10mm socket with a 3/8-inch ratchet to tighten the negative cable nut.
• Torque to 5 Nm (44 in-lbs) if using a torque wrench on the battery terminal clamp.
• Make sure the terminal does not rotate by hand after tightening.

Step 17: Bleed Air from the Cooling System

• Keep the coolant fill funnel kit installed and partly filled.
• Start your Fusion and set the cabin heat to warm.
• Let the engine idle while watching the coolant level in the funnel.
• Add coolant as the level drops.
• Use a flashlight to inspect the thermostat housing and hose connection for leaks.
• Stop the engine immediately if coolant leaks heavily or a temperature warning appears.

Step 18: Finish the Coolant Level

• Turn the vehicle OFF.
• Let it sit for several minutes.
• Use shop towels to carefully remove the coolant fill funnel kit.
• Install the coolant reservoir cap by hand until fully seated.
• After the engine cools completely, recheck the coolant level and top off if needed.

Step 19: Reinstall the Splash Shield and Lower the Vehicle

• If removed, position the lower splash shield under your Fusion.
• Use a 7mm socket, 8mm socket, or 10mm socket with a 3/8-inch ratchet to reinstall the fasteners.
• Tighten splash shield fasteners snug only.
• Use the floor jack rated 2-ton minimum to lift the vehicle slightly off the jack stands.
• Remove the jack stands, then lower the vehicle slowly to the ground.

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✅ After Repair

• ✅ Let your Fusion idle until it reaches normal temperature, then check for leaks.
• ✅ Take a short 10-15 minute test drive while watching for temperature warnings.
• ✅ After the vehicle cools completely, recheck coolant level in the reservoir.
• ✅ If the heater blows cold, the temperature rises, or you hear gurgling, air may still be trapped in the cooling system.
• ✅ Clean spilled coolant with shop towels. Coolant residue can attract pets and is poisonous.

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💰 DIY vs Shop Cost

Shop Cost: $250-$500 parts + labor

DIY Cost: $45-$140 parts only

You Save: $205-$360 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.5-2.5 hours.

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