Radiator Cap

Replacement of the radiator cap on a 2005 Dodge Viper 8.3L V10, requiring cooling system depressurization and verification of proper sealing.

Warnings

Tools required

Parts

• Radiator cap × 1 — Mopar 52079477AB or equivalent 16 PSI rated cap

Preparation

1. Ensure the engine is completely cold to the touch
2. Park the vehicle on level ground and engage the parking brake
3. Open the hood and locate the radiator cap on top of the radiator assembly at the front of the engine bay

Procedure

1. 1

   Verify Engine Temperature
   Touch the radiator cap area and upper radiator hose with your hand to confirm the cooling system is cold. If there is any warmth, wait longer before proceeding.
2. 2

   Relieve Residual Pressure
   Place a thick shop towel over the radiator cap. Press down on the cap while slowly turning it counterclockwise to the first stop (approximately 1/4 turn). Listen for any hissing sound indicating residual pressure. Wait until any hissing stops completely before proceeding.
3. 3

   Remove Radiator Cap
   Continue pressing down on the cap through the towel and turn it counterclockwise until it releases from the radiator neck. Lift the cap straight up and away from the filler neck.
4. 4

   Inspect Radiator Neck and Seal Surface
   Examine the radiator filler neck for any cracks, damage, or corrosion that could prevent proper sealing. Wipe the sealing surface clean with a shop towel to remove any debris or old coolant residue. Check the coolant level in the radiator; it should be visible near the top of the filler neck when cold.
5. 5

   Inspect Old Radiator Cap
   Examine the old cap's rubber sealing gasket and pressure relief valve on the underside. Look for cracking, hardening, torn rubber, or visible corrosion on the spring mechanism. Note that a deteriorated seal or failed pressure valve is the primary reason for replacement.
6. 6

   Install New Radiator Cap
   Verify the new cap's pressure rating matches the OEM cap marking for this vehicle (confirm the printed PSI/bar value on the original cap before selecting a replacement). Position the new cap over the radiator filler neck, aligning the tabs on the cap with the slots in the neck. Press down firmly and turn clockwise until the cap seats at the first stop, then continue turning until it locks into the fully seated position. You should feel distinct resistance at the final locking position.
7. 7

   Verify Cap Installation
   Ensure the cap is fully seated and locked by attempting to turn it slightly counterclockwise—it should not rotate beyond the locked position. The cap should sit flush and level on the radiator neck with no gaps visible.

Reassembly

1. No disassembly was required for this procedure

Verification

• Start the engine and allow it to reach normal operating temperature while monitoring for coolant leaks around the radiator cap
• After the engine reaches operating temperature, turn it off and allow it to cool for 30 minutes, then check that the cap remains properly seated
• Verify the cooling system maintains proper pressure by checking for coolant loss or cap loosening after the next few drive cycles
• Inspect the overflow reservoir to ensure coolant level is within the COLD range when the system has cooled completely

Related trouble codes on this vehicle

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