Replace the coolant bypass pipe on the 6.7L Cummins diesel engine, which routes coolant between the engine block and cooling system components.

Warnings

Tools required

Parts

• Coolant bypass pipe assembly × 1 — Use OEM specification
• O-rings for bypass pipe × 2 — Usually included with pipe assembly
• Hose clamps (if reusing is not advisable) × 2 — Use OEM specification

Fluids

• Mopar OAT Coolant (Purple) — 2 qt

Preparation

1. Ensure engine has been off for at least 2 hours and is completely cool to the touch
2. Park vehicle on level ground and engage parking brake
3. Place wheel chocks behind rear wheels
4. Disconnect negative battery terminal to prevent accidental cooling fan activation
5. Remove engine cover if equipped
6. Place drain pan under radiator drain location

Procedure

1. 1

   Drain cooling system
   Slowly loosen the radiator cap to relieve any residual pressure. Open the radiator drain petcock at the bottom of the radiator and allow coolant to drain into the pan. If equipped with a coolant drain plug on the engine block, remove it as well to ensure adequate drainage. Collect and properly store reusable coolant or dispose of contaminated coolant according to local regulations.
   Torque spec

   Drain Petcock9 Nm (7 lb-ft)

   Coolant Drain Plug15 Nm (11 lb-ft)
2. 2

   Access the bypass pipe
   The coolant bypass pipe is located on the driver's side of the engine near the thermostat housing and water pump. Remove any air intake components, harness brackets, or accessory drive components that obstruct access to the bypass pipe. Note the routing of all hoses and electrical connections before removal.
3. 3

   Disconnect hoses from bypass pipe
   Using hose clamp pliers or a flat blade screwdriver, loosen the hose clamps securing coolant hoses to the bypass pipe. Note the orientation and position of each hose for reassembly. Carefully twist and pull the hoses off the pipe nipples. If hoses are stuck, use a pick to gently break the seal between the hose and pipe, being careful not to damage the hose or mating surfaces.
4. 4

   Remove bypass pipe mounting fasteners
   Locate the housing bolts securing the bypass pipe to the engine block and/or thermostat housing. Remove these bolts using the appropriate socket and extensions. Support the bypass pipe while removing the final fastener to prevent it from falling. Keep track of bolt locations as lengths may vary.
   Torque spec

   Housing Bolts18 Nm (14 lb-ft)
5. 5

   Remove old bypass pipe
   Carefully extract the bypass pipe from the engine, noting the orientation and any alignment pins or guides. Inspect the pipe for cracks, corrosion, or other damage that caused the failure. Remove and discard all old O-rings from the mounting surfaces.
6. 6

   Clean mating surfaces
   Thoroughly clean all mating surfaces on the engine block, thermostat housing, and water pump where the bypass pipe seals. Remove any old gasket material, corrosion, or debris using a plastic scraper. Do not use metal scrapers that could damage the sealing surfaces. Wipe surfaces clean with a lint-free shop rag.
7. 7

   Install new O-rings and position new bypass pipe
   Lubricate new O-rings with a small amount of fresh coolant and install them in the grooves on the new bypass pipe. Verify O-rings are seated properly and not twisted. Carefully position the new bypass pipe into place, aligning it with the mounting holes and ensuring O-rings remain in position. Insert mounting bolts finger-tight.
8. 8

   Torque bypass pipe mounting bolts
   Using a torque wrench, tighten the bypass pipe housing bolts to specification in a criss-cross pattern to ensure even seating and prevent distortion. Start with the center bolts and work outward if multiple bolts are used.
   Torque spec

   Housing Bolts18 Nm (14 lb-ft)
9. 9

   Reconnect coolant hoses
   Inspect hoses for cracks, swelling, or deterioration and replace if necessary. Slide hoses onto the bypass pipe nipples, ensuring they are fully seated to the stop position. Position hose clamps approximately 1/4 inch from the end of each hose and tighten to specification. Ensure clamps are positioned away from the worm drive to prevent leaks.
   Torque spec

   Hose Clamps3 Nm (2 lb-ft)
10. 10

    Reinstall removed components
    Reinstall all air intake components, harness brackets, and accessory drive components that were removed for access. Ensure all connections are secure and routing matches the original configuration.
11. 11

    Close drain points and refill cooling system
    Close and torque the radiator drain petcock and engine block drain plug if applicable. Locate the cooling system bleed screw, typically on the thermostat housing or highest point of the cooling system. Open the bleed screw. Slowly fill the cooling system through the radiator or coolant reservoir with Mopar OAT Purple coolant mixed to 50/50 ratio with distilled water. Continue filling until coolant flows from the bleed screw without air bubbles, then close and torque the bleed screw. Fill the radiator to the top and the reservoir to the MAX COLD mark.
    Torque spec

    Bleed Screw9 Nm (7 lb-ft)

    Drain Petcock9 Nm (7 lb-ft)

    Coolant Drain Plug15 Nm (11 lb-ft)
12. 12

    Burp cooling system and check for leaks
    Reconnect the negative battery terminal. Install the radiator cap. Start the engine and allow it to reach normal operating temperature with the heater on high. Monitor the temperature gauge to ensure it stays within normal range. Watch for coolant leaks around the bypass pipe and all connections. As the thermostat opens, the coolant level may drop; turn off the engine, allow it to cool slightly, and top off the radiator and reservoir as needed. Repeat this process until the coolant level stabilizes.

Reassembly

1. Reinstall engine cover if equipped
2. After the first heat cycle, recheck all hose clamps and mounting bolts for proper torque
3. Top off coolant reservoir to MAX COLD line after engine has fully cooled

Verification

• Start the engine and verify no coolant leaks are present at the bypass pipe, hoses, or drain points
• Confirm engine reaches normal operating temperature (approximately 195-210°F) without overheating
• Verify heater provides hot air at idle and during driving
• Check coolant level in reservoir after the first complete heat cycle and top off if necessary
• Monitor coolant level over the next few days and inspect for any seepage or leaks
• Use a coolant hydrometer or refractometer to verify proper 50/50 mixture concentration for freeze and boil-over protection

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