🔧 3500 - Thermostat Replacement

On your 3500’s 6.4L engine, the thermostat controls when coolant flows to the radiator. If it sticks open you may get low operating temp/poor heat; if it sticks closed you can overheat.

Difficulty Level: Intermediate | Estimated Time: 1.0-2.0 hours

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⚠️ Safety & Precautions

• ⚠️ Never open the coolant system hot; let the engine cool fully.
• ⚠️ Coolant is toxic—use a drain pan and keep away from kids/pets.
• ⚠️ Keep hands/tools away from the cooling fan and belt drive.
• Disconnecting the battery is not required, but it’s safer if you’re new: remove the negative cable before working near the fan.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• Drain pan (at least 3-gallon)
• Funnel
• Shop rags
• 10mm socket
• 1/4" drive ratchet
• 3" extension (1/4" drive)
• Torque wrench (inch-pound)
• Hose clamp pliers
• Flat-blade screwdriver
• 8mm nut driver
• Pliers
• Floor jack (rated 3-ton minimum)
• Jack stands (rated 3-ton minimum)
• Wheel chocks

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Engine thermostat (6.4L) - Qty: 1
• Thermostat seal/O-ring (if not included) - Qty: 1
• Engine coolant (Mopar OAT 10-year/150k compatible) - Qty: 1-2 gallons (as needed)
• Distilled water (if using concentrate coolant) - Qty: 1-2 gallons (as needed)
• Hose clamps (optional, if originals are weak) - Qty: 1-2

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📋 Before You Begin

• Park on level ground, set the parking brake, and chock the wheels.
• Let the engine cool completely (upper radiator hose should feel cool).
• If you need more access, raise the front with a floor jack and support with jack stands.
• Place a drain pan under the radiator drain area before opening anything.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Relieve pressure safely

• Slowly loosen the coolant reservoir cap (or radiator cap if equipped) only when the engine is fully cool.
• Use nitrile gloves and safety glasses.

Step 2: Drain enough coolant

• Position the drain pan under the radiator drain.
• Open the radiator drain (use pliers or flat-blade screwdriver, depending on the style).
• Drain until the coolant level is below the thermostat housing level. You don’t need to drain it completely.

Step 3: Remove the intake ducting (as needed for access)

• Loosen the intake tube clamps using an 8mm nut driver or flat-blade screwdriver.
• Remove any fasteners holding the intake tube/air box if they block access (use a 10mm socket and ratchet).
• Move the ducting aside so you can reach the thermostat housing.

Step 4: Remove the upper radiator hose from the thermostat housing

• Use hose clamp pliers to compress the clamp and slide it back on the hose.
• Twist the hose gently to break it free, then pull it off the thermostat housing.
• Have shop rags ready for spill control.

Step 5: Remove the thermostat housing

• Remove the thermostat housing bolts using a 10mm socket, 1/4" ratchet, and extension.
• Lift off the housing and remove the thermostat.
• Clean the sealing surfaces with shop rags (no gouging). Clean and flat surfaces prevent leaks.

Step 6: Install the new thermostat and seal

• Install the new thermostat with the correct orientation (if it has a small “jiggle valve,” point it at the top, about 12 o’clock).
• Install the new seal/O-ring in its groove (make sure it’s not twisted or pinched).

Step 7: Reinstall the housing and torque bolts

• Set the housing back in place and start the bolts by hand.
• Tighten evenly using a 10mm socket and ratchet.
• Final tighten with a torque wrench (inch-pound): Torque to 12 Nm (106 in-lbs).

Step 8: Reconnect the upper hose and intake ducting

• Reinstall the upper radiator hose and position the clamp using hose clamp pliers.
• Reinstall the intake ducting and tighten clamps using an 8mm nut driver or flat-blade screwdriver.

Step 9: Refill and bleed air from the cooling system

• Close the radiator drain.
• Refill coolant slowly using a funnel with the correct Mopar OAT-compatible coolant mix.
• Start the engine and set the heater to MAX HEAT (this opens the heater circuit).
• Let it idle and watch temperature. As it warms up, top off as needed. Don’t overfill the reservoir.
• Once you feel strong heat from the vents and the upper radiator hose gets hot, the thermostat has opened.
• Shut the engine off, let it cool, then recheck and top off the coolant level.

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✅ After Repair

• Check carefully for leaks around the thermostat housing and the upper radiator hose.
• Test drive and confirm the temperature gauge rises normally and stays stable.
• After the next full cool-down (later that day or next morning), recheck coolant level and top off if needed.
• If you have a check-engine light or temp warning after the repair, stop and recheck for trapped air or a leak.

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💰 DIY vs Shop Cost

Shop Cost: $250-$550 (parts + labor)

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

You Save: $210-$410 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.0-2.0 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.