Radiator Cap

Remove and replace the radiator cap on a 2008 Dodge Viper 8.4L V10 to restore proper cooling system pressure and prevent coolant loss.

Warnings

Tools required

Parts

• Radiator cap × 1 — Mopar 68079744AA or equivalent 18 PSI cap

Preparation

1. Ensure the engine has been off for at least 2 hours and is completely cold to the touch
2. Verify the vehicle is parked on level ground with the parking brake engaged
3. Open the hood and locate the radiator cap on the radiator neck at the front of the engine bay, driver's side of the radiator

Procedure

1. 1

   Verify cooling system is depressurized
   Place your hand near (but not on) the radiator cap and verify the engine is cold. Listen for any hissing sounds that would indicate residual pressure in the cooling system. If any pressure sounds are present, wait longer for the system to fully cool and depressurize.
2. 2

   Remove old radiator cap
   Place a clean shop towel over the radiator cap to catch any residual coolant spray. Press down firmly on the cap and rotate counterclockwise to the first detent (approximately 1/4 turn) to release any remaining pressure. Pause for 5-10 seconds to allow pressure equalization. Press down again and continue rotating counterclockwise until the cap releases completely from the radiator neck. Lift the cap straight up and away.
3. 3

   Inspect radiator neck and cap seat
   Examine the radiator filler neck for cracks, corrosion, or damage to the sealing surface. Check that the rubber sealing surfaces where the cap mates are clean and free of debris, old coolant residue, or damage. Wipe clean with a shop towel if necessary. If the neck shows damage or deep corrosion, the radiator may require replacement or repair before a new cap will seal properly.
4. 4

   Check coolant level
   With the cap removed, look into the radiator filler neck and verify coolant is visible near the top of the neck. The coolant should be at or just below the base of the filler neck. If coolant level is low, top off with the Mopar-specified coolant for this vehicle (verify correct type against service documentation) in a 50/50 mixture before installing the new cap. Low coolant may indicate a leak or cap failure that allowed coolant to escape.
5. 5

   Install new radiator cap
   Inspect the new radiator cap to ensure both rubber seals (pressure seal and safety seal) are present and in good condition. Align the cap with the radiator neck and press down firmly. Rotate clockwise until the cap engages and locks into place with a firm click or stop. The cap should require approximately 1/4 to 1/2 turn to fully seat and lock.

Reassembly

1. No additional reassembly required beyond cap installation

Verification

• After installation, attempt to remove the cap by pulling upward without pressing down - it should not release, confirming proper lock engagement
• Start the engine and allow it to reach operating temperature while monitoring for coolant leaks around the cap
• After the engine reaches operating temperature, shut it off and allow it to cool for 30 minutes, then verify the cap remains secure and shows no signs of coolant seepage
• Check the coolant overflow reservoir to ensure the level is within the MIN/MAX marks after the cooling system has pressurized and de-pressurized through a heat cycle

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