Thermostat

Replace the thermostat and housing gasket on a 2008 Dodge Viper 8.4L V10, requiring coolant drain, upper radiator hose removal, and housing disassembly.

Warnings

Tools required

Parts

• Thermostat × 1 — Mopar 05080338AA or equivalent 195°F
• Thermostat housing gasket × 1 — Use OEM specification
• Upper radiator hose clamp (if damaged) × 1 — Use OEM specification

Fluids

• Mopar HOAT coolant 50/50 — 2 qt

Preparation

1. Ensure engine is completely cold (wait minimum 2 hours after last operation)
2. Position vehicle on level surface and apply parking brake
3. Place drain pan under radiator drain petcock on driver side of radiator
4. Open radiator cap slowly to release any residual pressure

Procedure

1. 1

   Drain coolant
   Open the radiator drain petcock located at the bottom driver side of the radiator. Allow coolant to drain into the catch pan until flow stops. Close the petcock after draining. You do not need to drain the entire system, but draining 2-3 gallons will prevent excessive spillage during thermostat housing removal.
2. 2

   Remove upper radiator hose
   Locate the upper radiator hose connection at the thermostat housing on the front of the engine. Use hose clamp pliers to compress and slide the spring clamp back approximately 2 inches from the housing connection. Twist the hose gently to break the seal, then pull it straight off the thermostat housing neck. Have a shop towel ready as residual coolant will drain from the hose.
3. 3

   Remove thermostat housing bolts
   Locate the thermostat housing at the front center of the engine block, below the throttle body assembly. Remove the bolts securing the thermostat housing to the engine block using a socket of the appropriate size. Verify the exact bolt count and size against the factory service manual for the 2008 Viper 8.4L V10. Note the bolt lengths and positions if they differ for reassembly.
4. 4

   Remove thermostat housing and thermostat
   Pull the thermostat housing straight away from the engine block. The thermostat will either remain in the housing or stay seated in the engine block recess. Remove the thermostat and note its orientation—the spring side faces toward the engine block, and the pellet/valve side faces outward. Remove and discard the old gasket or O-ring seal.
5. 5

   Clean mating surfaces
   Use a plastic scraper or gasket removal tool to carefully clean all old gasket material from both the thermostat housing mating surface and the engine block recess. Avoid scratching the aluminum surfaces. Wipe clean with a shop towel. Inspect both surfaces for cracks, warping, or damage. Use a wire brush to clean any corrosion from the recess, then wipe with a clean shop towel.
6. 6

   Install new thermostat
   Place the new thermostat into the engine block recess with the spring side facing INTO the engine block and the pellet/valve side facing outward toward you. Ensure the thermostat seats fully into the recess and aligns with any locating pins or notches. The thermostat should sit flat and flush in the recess.
7. 7

   Install new gasket and housing
   Position the new gasket over the thermostat and align it with the bolt holes in the engine block. Carefully place the thermostat housing over the gasket and thermostat, ensuring the housing neck aligns properly and does not disturb the thermostat position. Start both housing bolts by hand to ensure proper thread engagement.
8. 8

   Torque housing bolts
   Using a torque wrench, tighten the thermostat housing bolts in an alternating pattern to the manufacturer-specified torque. Start with finger-tight, then torque in two stages to ensure even gasket compression. Verify the exact torque value against the factory service manual for the 2008 Viper 8.4L V10.
   Torque spec

   Thermostat Housing Bolts15 Nm (11 lb-ft)
9. 9

   Reconnect upper radiator hose
   Inspect the inside of the upper radiator hose end for cracks or deterioration. Slide the hose fully onto the thermostat housing neck until it bottoms against the bead. Slide the spring clamp back into position over the connection point, approximately 1/2 inch from the housing bead. Ensure the clamp is seated in the groove on the housing neck.
10. 10

    Refill cooling system
    Using a funnel, slowly pour Mopar HOAT 50/50 coolant mixture into the radiator fill neck. Fill until coolant reaches the base of the fill neck. Allow time for air bubbles to escape. Start the engine and let it idle with the radiator cap off. Follow the factory bleed procedure for the 2008 Viper V10. As the thermostat opens (approximately 195°F), coolant level will drop. Continue adding coolant to maintain level. Continue adding coolant to maintain level at the base of the fill neck. Run engine until cooling fans cycle on, then turn off engine.
11. 11

    Final fill and pressure test
    After engine cools for 10 minutes, check coolant level and top off to the base of the fill neck. Install the radiator cap securely. Check the overflow reservoir and fill to the COLD line if needed. Inspect all connections for leaks, particularly around the thermostat housing and upper radiator hose. Start engine and bring to operating temperature while monitoring for leaks and proper temperature gauge operation.

Reassembly

1. Torque thermostat housing bolts in alternating pattern to prevent gasket distortion
2. Ensure upper radiator hose is fully seated on housing neck before securing clamp
3. Refill coolant slowly to allow air pockets to escape naturally

Verification

• Start engine and verify temperature gauge reaches normal operating range (approximately 195-210°F)
• Confirm upper radiator hose becomes hot and firm when thermostat opens, indicating proper coolant flow
• Check for coolant leaks around thermostat housing and upper radiator hose connection after engine reaches operating temperature
• Verify cooling fans cycle on at appropriate temperature
• After test drive, recheck coolant level when engine is cold and top off if necessary

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