Radiator Cap

This procedure covers the inspection and replacement of the radiator cap on a 2007 Ram 3500 with the 5.9L Cummins diesel engine.

Warnings

Tools required

Parts

• Radiator cap × 1 — Use OEM Mopar specification (16 PSI cap)

Fluids

• HOAT coolant 50/50 — 0.25 qt

Preparation

1. Ensure the engine is completely cold to the touch
2. Park vehicle on level ground and engage parking brake
3. Open the hood and secure with the prop rod
4. Locate the radiator cap on top of the radiator behind the grille

Procedure

1. 1

   Verify engine temperature
   Place your hand near (not on) the radiator cap and upper radiator hose to confirm the engine is completely cold. If any heat is detected, wait longer before proceeding. Use OEM Mopar specification cap. The factory cap is commonly rated around 14-15 PSI. Verify exact PSI rating against factory service documentation.
2. 2

   Relieve cooling system pressure
   Place a shop towel over the radiator cap. Slowly turn the cap counterclockwise to the first stop position and wait for any residual pressure to release. You should hear a brief hissing sound if any pressure remains. Wait until all hissing stops completely.
3. 3

   Remove radiator cap
   Once all pressure is released, press down on the cap while continuing to turn counterclockwise past the first stop until the cap releases from the radiator neck. Lift the cap straight up and away from the radiator.
4. 4

   Inspect radiator neck and sealing surface
   Examine the radiator filler neck for cracks, damage, or corrosion. Check the rubber seal surface on the neck for deterioration or debris. Clean any dirt or debris from the sealing surface with a clean shop towel. Inspect the coolant level and condition in the radiator.
5. 5

   Inspect old radiator cap
   Examine the old cap's rubber seals (both the lower seal and the pressure relief seal) for cracks, hardening, or deterioration. Check the spring mechanism for proper tension. A faulty seal or weak spring indicates cap replacement is necessary.
6. 6

   Install new radiator cap
   Place the new radiator cap onto the radiator neck, aligning the tabs on the cap with the slots in the neck. Press down firmly and turn clockwise until the cap seats against the first stop, then continue turning until it reaches the locked position. The cap should sit flush against the radiator neck.
7. 7

   Check coolant level
   With the cap removed temporarily, verify the coolant level is visible at the top of the radiator neck. If low, add the factory-specified 50/50 coolant mixture (verify coolant type against service documentation) until the level reaches the base of the filler neck. Reinstall the radiator cap securely.

Reassembly

1. Ensure the radiator cap is fully seated and locked in position
2. Wipe any spilled coolant from the radiator and surrounding components
3. Check the coolant overflow reservoir level and top off to the FULL COLD mark if needed

Verification

• Start the engine and allow it to reach normal operating temperature while monitoring for leaks around the radiator cap
• Observe the temperature gauge to ensure the engine maintains normal operating temperature (approximately 180-210°F)
• After the engine cools completely, recheck the radiator cap for proper seating and check coolant level again
• Inspect for any coolant seepage or staining around the radiator cap area after several drive cycles

Related trouble codes on this vehicle

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