🔧 Optima - Thermostat Replacement

On your Optima, the thermostat sits in the coolant outlet/inlet housing where the radiator hose meets the engine. Replacing it restores proper coolant flow so the engine warms up normally and doesn’t overheat.

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

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⚠️ Safety & Precautions

• ⚠️ Only work on a fully cold engine; hot coolant can cause severe burns.
• ⚠️ Coolant is toxic; use a catch pan and clean spills immediately.
• ⚠️ Support the car with jack stands; never rely on a jack alone.
• Disconnecting the battery is not required, but keep tools clear of the radiator fan (it can come on unexpectedly).

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• Wheel chocks
• Floor jack (rated 3-ton minimum)
• Jack stands (rated 3-ton minimum)
• Trim clip removal tool
• Drain pan (at least 2-gallon)
• Funnel
• Shop rags
• Flat-blade screwdriver
• Hose clamp pliers
• 10mm socket
• 12mm socket
• 3/8" ratchet
• 3" extension
• Torque wrench (5–60 Nm range)

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Engine thermostat - Qty: 1
• Thermostat O-ring / gasket - Qty: 1
• Hyundai/Kia long-life coolant (P-OAT) - Qty: 2 gallons (premix)
• Replacement hose clamp - Qty: 1 (optional)

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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 2+ hours).
• Set the cabin heat to HOT during the bleed step later (this helps purge air).

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Raise the front and remove the lower splash shield

• Use floor jack (rated 3-ton minimum) to lift the front safely and place the car on jack stands (rated 3-ton minimum).
• Remove the lower engine cover/splash shield using a trim clip removal tool and 10mm socket.

Step 2: Relieve cooling system pressure

• Slowly loosen the coolant reservoir cap by hand. If you hear pressure, stop and wait until it’s fully released.
• Cold engine only.

Step 3: Drain the coolant

• Place a drain pan (at least 2-gallon) under the radiator drain area.
• Open the radiator drain cock using a flat-blade screwdriver (some drain cocks are hand-turn; use the screwdriver only if needed).
• Let coolant drain fully, then close the drain cock snugly.

Step 4: Locate the thermostat housing

• From the front of the engine bay, follow the lower radiator hose to where it connects to the engine—this connection is the thermostat housing area.
• If access is tight, remove the intake snorkel/duct clamps using a flat-blade screwdriver and move the ducting aside.

Step 5: Remove the lower radiator hose from the housing

• Use hose clamp pliers to compress the spring clamp and slide it back on the hose.
• Twist and pull the hose off the housing. Catch any remaining coolant with the drain pan.
• Twist first to break the seal.

Step 6: Remove the thermostat housing

• Remove the housing bolts using a 10mm socket (some fasteners in this area may be 12mm socket depending on the housing/bracket).
• Pull the housing straight off. Keep track of the thermostat orientation before removing it.
• Clean the mating surfaces using shop rags. Do not gouge aluminum surfaces.

Step 7: Install the new thermostat and seal

• Install the new thermostat in the same orientation as removed.
• Install the new thermostat O-ring / gasket. Make sure it sits flat and is not pinched.
• Reinstall the housing and hand-thread bolts first.
• Tighten housing bolts evenly using a torque wrench: Torque to 9.8 Nm (7 ft-lbs).

Step 8: Reconnect the hose and reassemble access parts

• Reinstall the lower radiator hose and position the clamp using hose clamp pliers.
• Reinstall any intake ducting removed using a flat-blade screwdriver.
• Reinstall the splash shield using a trim clip removal tool and 10mm socket.
• Lower the car using the floor jack (rated 3-ton minimum).

Step 9: Refill and bleed air from the cooling system

• Fill the reservoir with Hyundai/Kia long-life coolant (P-OAT) using a funnel until it reaches the MAX line.
• Start the engine and set the heater to HOT with the fan on low.
• Let the engine idle and warm up until the radiator fan cycles at least once.
• Shut the engine off, let it cool, then top off coolant to the MAX line as needed.
• Check the thermostat housing and hose connection for leaks using safety glasses and a flashlight (use your phone light if needed).

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✅ After Repair

• Take a 10–15 minute test drive while watching the temperature gauge.
• After the engine cools completely, recheck the reservoir level and top off to MAX if needed.
• Inspect for dried coolant tracks around the housing and hose clamp the next day.

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💰 DIY vs Shop Cost

Shop Cost: $350-$700 (parts + labor)

DIY Cost: $40-$140 (parts only)

You Save: $310-$560 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?

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