Radiator Hose - Upper

This procedure covers removal and replacement of the upper radiator hose on the 5.9L Cummins diesel engine, requiring coolant drainage and refilling.

Warnings

Tools required

Parts

• Upper radiator hose × 1 — 5.9L Cummins diesel specific
• Hose clamps (if reusing originals is not advisable) × 2 — Worm-drive or spring clamps to match original

Fluids

• Ethylene glycol 50/50 (green conventional early, HOAT later) — 2 qt

Preparation

1. Ensure engine is completely cold to the touch (at least 2 hours after last operation)
2. Park vehicle on level ground and apply parking brake
3. Place drain pan beneath radiator drain petcock
4. Have replacement coolant ready and accessible

Procedure

1. 1

   Drain coolant from radiator
   Open the radiator drain petcock at the bottom of the radiator by turning counterclockwise. Allow coolant to drain into the drain pan until the level is below the upper radiator hose connection point. You do not need to drain the entire system. Close the petcock hand tight when finished.
   Torque spec

   Drain Petcock7 Nm (5 lb-ft)
2. 2

   Remove radiator cap
   Remove the radiator cap from the top of the radiator to allow air into the system and facilitate complete drainage from the upper hose area. This prevents vacuum lock when removing the hose.
3. 3

   Loosen upper hose clamp at radiator
   Locate the hose clamp securing the upper radiator hose to the radiator neck. Use a flathead screwdriver or nut driver to loosen the clamp completely. Slide the clamp back along the hose away from the radiator connection, at least 2-3 inches.
4. 4

   Loosen upper hose clamp at thermostat housing
   Locate the hose clamp at the engine side of the upper radiator hose where it connects to the thermostat housing on the front of the cylinder head. Loosen this clamp and slide it back along the hose away from the connection point.
5. 5

   Remove upper radiator hose
   Twist the hose gently at both connection points to break the seal, then pull the hose off the radiator neck and thermostat housing. If the hose is stuck due to age, carefully use a flathead screwdriver to gently pry between the hose and fitting - be careful not to damage the radiator neck or thermostat housing. Residual coolant will drain from the hose.
6. 6

   Inspect connection points
   Inspect the radiator neck and thermostat housing for any damage, corrosion, or debris. Clean both surfaces with a shop towel. Check for cracks or damage that could cause leaks with the new hose. If the thermostat housing shows significant corrosion, consider replacement.
7. 7

   Install new upper radiator hose
   Position new hose clamps on the new hose before installation. Slide the hose onto the thermostat housing first, ensuring it seats completely onto the fitting. Then connect the radiator end, ensuring it is fully seated on the radiator neck. The hose should fit snugly without excessive force.
8. 8

   Secure hose clamps
   Position the hose clamps approximately 1/2 inch from the end of each hose connection. Tighten the clamp at the thermostat housing first, then the radiator neck clamp. If using worm-drive clamps, tighten to approximately 40 in-lbs (4.5 Nm), or until snug against the hose bead without cutting into the hose. Ensure clamps are positioned over the hose bead on each fitting.
   Torque spec

   Hose Clamps3 Nm (2 lb-ft)
9. 9

   Refill cooling system
   Using a funnel, pour the appropriate coolant type into the radiator until it reaches the bottom of the filler neck. Fill slowly to allow air to escape. Add coolant as needed to bring level to proper fill point; expect to add several quarts since draining below the upper hose can release a gallon or more from this large Cummins cooling system.
10. 10

    Burp cooling system
    With the radiator cap still off, start the engine and allow it to warm up to operating temperature (approximately 190-210°F). Watch the coolant level and add coolant as needed as air purges from the system. The upper radiator hose should become hot to the touch, indicating the thermostat has opened. Maintain coolant level at the bottom of the filler neck.
11. 11

    Final fill and cap installation
    Once the engine reaches operating temperature and no more air bubbles emerge, top off the coolant to the proper level. Install the radiator cap securely. Check the coolant overflow reservoir and fill to the cold fill line if needed.

Reassembly

1. No disassembly was required beyond hose removal - all components are already reassembled during the procedure

Verification

• With engine at operating temperature, visually inspect both hose connections for any signs of coolant leakage
• Check that the upper radiator hose is firm when engine is warm, indicating proper system pressure
• Verify coolant level is correct in both the radiator (when cool) and overflow reservoir
• After 24-48 hours of driving, recheck coolant level and inspect connections again for any seepage
• Monitor engine temperature gauge during first few drives to ensure normal operating temperature is maintained

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

Chasing one of these codes and not sure which part is guilty? Ask a master mechanic about YOUR car →

More procedures for this vehicle