Coolant Bypass Pipe

Replace the coolant bypass pipe on a 2007 Ram 3500 with 5.9L Cummins diesel engine to fix coolant leaks or corrosion at the bypass tube assembly.

Warnings

Tools required

Parts

• Coolant bypass pipe assembly × 1 — Use OEM specification
• O-rings for bypass pipe × 2 — Use OEM specification
• Hose clamps × 4 — As needed for replacement
• Coolant bypass hoses × 1 — Inspect and replace if degraded

Fluids

• HOAT coolant 50/50 — 4 qt

Preparation

1. Ensure engine is completely cold before beginning work
2. Park vehicle on level surface and engage parking brake
3. Disconnect negative battery cable to prevent accidental fan engagement
4. Place drain pan under radiator drain valve
5. Remove engine cover if equipped
6. Locate the coolant bypass pipe on the driver's side front of the engine block near the water pump

Procedure

1. 1

   Drain coolant system
   Open the radiator drain valve (petcock) at the bottom of the radiator and allow coolant to drain into the drain pan. Drain approximately 1-2 gallons or until coolant level is below the bypass pipe location on the engine block. Close the drain valve once adequate coolant has been removed.
2. 2

   Remove intake air components
   Remove the intake air tube from the turbocharger inlet to the air filter box to improve access to the bypass pipe area. Loosen hose clamps and disconnect any electrical connectors for sensors. Set components aside in a clean area.
3. 3

   Disconnect coolant hoses from bypass pipe
   Locate the coolant hoses connected to the bypass pipe assembly. Use hose clamp pliers or standard pliers to release the hose clamps. Carefully twist and pull the hoses off the bypass pipe fittings. Be prepared for residual coolant spillage. If hoses are stuck, carefully work them loose without damaging the nipples.
4. 4

   Remove bypass pipe mounting hardware
   Locate and remove the bolts securing the coolant bypass pipe to the engine block. Verify the number and location of bypass pipe mounting bolts against factory service documentation before removal. Use a socket and extension to access these bolts from above and below as needed. Keep track of all hardware for reinstallation.
5. 5

   Extract old bypass pipe
   Carefully work the bypass pipe out of its mounting location. The pipe may have O-rings seated in the engine block that create resistance. Gently twist and pull the pipe assembly free. If the pipe is corroded in place, carefully use penetrating oil and allow it to soak before attempting removal again. Avoid damaging the mating surfaces on the engine block.
6. 6

   Clean mating surfaces
   Carefully clean the O-ring sealing bores and mounting surfaces on the engine block, removing corrosion and debris without scratching the machined sealing surfaces. Do not aggressively scrape the O-ring bores. Wipe clean with shop towels and inspect the bores for damage or deep corrosion that could prevent proper sealing. Wipe clean with shop towels. Inspect the bores in the engine block for damage or deep corrosion that could prevent proper sealing.
7. 7

   Prepare new bypass pipe
   Unpack the new bypass pipe assembly and verify it matches the old part. Install new O-rings onto the pipe ends, ensuring they are seated properly in their grooves. Lightly lubricate the O-rings with clean coolant to aid installation and prevent tearing.
8. 8

   Install new bypass pipe
   Carefully align the new bypass pipe with the mounting holes and bores in the engine block. Push the pipe into position, ensuring the O-rings seat properly without rolling or pinching. The pipe should slide in with firm, even pressure. Do not force it if significant resistance is encountered.
9. 9

   Secure bypass pipe mounting bolts
   Install the mounting bolts and hand-tighten them first to ensure proper alignment. Then tighten the bolts evenly to the factory-specified torque (typically small M6/M8 fasteners, approximately 7-17 ft-lbs depending on bolt size). Always confirm the exact torque value in factory service documentation. If not, tighten bolts firmly but do not over-torque as this can crack the pipe or damage threads.
10. 10

    Reconnect coolant hoses
    Inspect the coolant hoses for cracks, swelling, or degradation. Replace if necessary. Slide hoses onto the bypass pipe fittings and ensure they are fully seated past the bead on each nipple. Install new hose clamps and position them 1/4 inch from the end of each hose. Tighten clamps securely.
11. 11

    Reinstall intake air components
    Reinstall the intake air tube and reconnect all hose clamps and electrical connectors that were removed during disassembly. Ensure all connections are secure and properly seated.
12. 12

    Refill and bleed cooling system
    Reconnect the negative battery cable. Add the manufacturer-specified 50/50 coolant mixture (fully-formulated coolant meeting Cummins/Mopar specification with proper SCA/nitrite protection for the diesel engine) to the radiator and overflow reservoir to the proper level. Fill through the coolant pressure bottle to the proper level with the cap off, then start the engine and allow it to warm up to operating temperature, monitoring the level and adding coolant as needed before installing the pressure cap. Watch for coolant circulation and air bubbles. Add coolant as needed to maintain proper level. Squeeze upper radiator hose to help purge air pockets. Once thermostat opens and coolant circulates fully, top off radiator and reservoir. Install radiator cap.

Reassembly

1. Verify all hose clamps are tight and properly positioned on the bypass pipe connections
2. Reinstall engine cover if it was removed during preparation
3. Double-check that all tools and parts have been removed from the engine compartment
4. Inspect the work area for any coolant spills and clean as necessary

Verification

• With engine at normal operating temperature, inspect the bypass pipe and all connections for any signs of coolant leaks
• Check coolant level in the overflow reservoir after the engine has cooled completely and top off if necessary
• Monitor coolant level and temperature gauge over the next few days of driving to ensure the repair is successful
• Verify that the cooling system maintains proper pressure and temperature under normal driving conditions

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