Thermostat

Replace the engine thermostat and housing gasket on a 2005 Dodge Viper 8.3L V10, including coolant drain and refill with proper bleeding procedure.

Warnings

Tools required

Parts

• Thermostat × 1 — Use OEM specification (180°F or 195°F as original)
• Thermostat housing gasket × 1 — Use OEM specification
• Coolant temperature sensor (if damaged) × 1 — Use OEM specification

Fluids

• Zerex G-05 HOAT 50/50 coolant — 4 qt

Preparation

1. Ensure engine is completely cold (at least 2 hours after last operation)
2. Park vehicle on level surface and engage parking brake
3. Place drain pan under radiator drain petcock location
4. Have replacement thermostat, gasket, and coolant ready before starting

Procedure

1. 1

   Drain cooling system
   Open the radiator drain petcock located at the bottom driver's side of the radiator. Allow coolant to drain into the collection pan. Once flow has stopped, close the petcock. You do not need to drain the entire system—draining the radiator is sufficient for thermostat replacement.
2. 2

   Locate thermostat housing
   The thermostat housing is located on the front of the engine, slightly toward the driver's side, where the radiator hose connects to the engine. Verify against the service manual whether the thermostat is on the upper (outlet) or lower (inlet) hose connection before proceeding, as this determines hose disconnection order. Identify the housing and its mounting bolts before proceeding.
3. 3

   Disconnect lower radiator hose
   Loosen the hose clamp securing the radiator hose to the thermostat housing (verify upper vs lower per service manual). Twist and pull the hose off the housing neck. Be prepared for residual coolant to drain—position a drain pan or shop towels accordingly.
4. 4

   Remove thermostat housing bolts
   Remove the bolts securing the thermostat housing to the engine (verify exact count—typically 2 to 4—against the service manual). Note their positions and retrieve any washers if present. Set bolts aside in a clean location.
5. 5

   Remove thermostat housing and old thermostat
   Pull the thermostat housing away from the engine block. The thermostat will either be seated in the housing or in the engine block recess. Remove the thermostat and note its exact orientation before removal—the spring/sensing element must face toward the engine coolant side. Reference the removed unit and the service manual to confirm correct installation orientation. Remove and discard the old gasket from both mating surfaces.
6. 6

   Clean mating surfaces
   Use a gasket scraper or plastic scraping tool to thoroughly clean both the engine block and thermostat housing mating surfaces. Remove all traces of old gasket material, corrosion, or debris. Wipe clean with shop towels. Do not gouge or scratch the aluminum surfaces.
7. 7

   Install new thermostat
   Place the new thermostat into the engine block recess with the spring side facing into the engine and the pellet side facing outward. Ensure the thermostat seats fully in the recess and that any alignment pin or notch is properly positioned.
8. 8

   Install new gasket and housing
   Position the new gasket over the thermostat, aligning any bolt holes or locating features. Place the thermostat housing over the gasket and align the bolt holes. Start both bolts by hand to ensure proper threading and alignment before tightening.
   Torque spec

   Thermostat Housing Bolt15 Nm (11 lb-ft)
9. 9

   Torque thermostat housing bolts
   Torque the thermostat housing bolts to the manufacturer-specified value (verify in service manual; typically in the 12–25 Nm / 9–18 lb-ft range for aluminum housings) in a cross pattern to ensure even gasket compression. Do not overtighten as the housing is aluminum and can be damaged.
   Torque spec

   Thermostat Housing Bolt15 Nm (11 lb-ft)
10. 10

    Reconnect lower radiator hose
    Slide the lower radiator hose back onto the thermostat housing neck. Ensure it is fully seated and position the hose clamp over the beaded section of the housing neck. Tighten the clamp securely.
11. 11

    Refill cooling system
    Remove the radiator cap and fill the radiator with Zerex G-05 HOAT 50/50 coolant until it reaches the base of the filler neck. Note the full system capacity for the 8.3L V10 is significantly more than 4 quarts—verify total capacity in the service manual and have adequate coolant on hand. Also fill the coolant recovery reservoir to the FULL COLD mark. Start with approximately 3-4 quarts and monitor level during bleeding process.
12. 12

    Bleed cooling system
    Start the engine and allow it to idle with the radiator cap off. Monitor coolant level and add coolant as the level drops when air purges from the system. Gently squeeze the upper radiator hose to help release air pockets. Run the engine until the thermostat opens (you will see coolant circulation increase and temperature gauge rise to normal operating range). Continue to add coolant as needed until the level stabilizes.
13. 13

    Final fill and cap installation
    With the engine at operating temperature and coolant circulating, top off the radiator to the base of the filler neck. Install the radiator cap securely. Check the coolant recovery reservoir level and adjust to the FULL HOT mark if engine is at operating temperature. Shut off the engine.
14. 14

    Check for leaks
    Inspect the thermostat housing, lower radiator hose connection, and radiator drain petcock for any signs of coolant leakage. Wipe the area clean and watch for fresh coolant seepage. If leaks are present, address immediately before proceeding.

Reassembly

1. Installation follows removal in reverse order
2. Always use a new thermostat gasket—do not reuse the old gasket
3. Ensure the thermostat is oriented correctly with spring side toward engine block
4. Proper bleeding is essential—take time to ensure all air is purged from the system

Verification

• Start engine and verify it reaches normal operating temperature without overheating
• Confirm coolant circulates through upper radiator hose when thermostat opens
• Check that cabin heater produces hot air, indicating proper coolant flow
• Verify no coolant leaks are present at thermostat housing or hose connections
• After cool-down, recheck coolant level and top off as needed—some air may continue to purge over the first few heat cycles

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