Cummins Engine Coolant Leak in 855 Series: Causes, Diagnosis, and Repair

[MikePhua]

Coolant leaks in Cummins 855 engines, a popular heavy-duty diesel engine series, present a common maintenance challenge that can lead to engine overheating, damage, and operational downtime. Understanding the causes, detection methods, and repair options is critical for keeping the engine running reliably.

Common Causes of Coolant Leaks in Cummins 855 Engines

• Worn or Damaged Hoses
  

Coolant hoses degrade over time due to heat and pressure cycles, leading to cracks, splits, or loose fittings.

• Faulty Water Pump Seals
  

Water pump seals can fail, causing leaks around the pump housing and reducing coolant circulation.

• Radiator or Heater Core Leaks
  

Corrosion or impact damage to the radiator or heater core results in coolant seepage.

• Gasket Failures
  

Head gasket or intake manifold gaskets can deteriorate, allowing coolant to escape internally or externally.

• Freeze Plug Failure
  

Corrosion or physical damage to freeze plugs leads to coolant leakage around the engine block.

Symptoms Indicating Coolant Leak

• Visible coolant puddles under the engine or vehicle.
  
• Low coolant level in the reservoir requiring frequent refills.
  
• Engine overheating warnings or temperature gauge rising beyond normal range.
  
• White smoke from the exhaust (indicative of coolant burning in the combustion chamber).
  
• Sweet smell from leaking coolant around the engine area.
  

Diagnostic Procedures

• Visual Inspection
  

Check all coolant hoses, clamps, water pump area, radiator, and freeze plugs for wetness or corrosion.

• Pressure Test
  

Use a cooling system pressure tester to identify leaks under controlled pressure conditions.

• Dye Testing
  

Add UV dye to coolant and inspect with a UV light to pinpoint small or hidden leaks.

• Check for Internal Leaks
  

Perform a compression test or chemical test for combustion gases in coolant indicating head gasket issues.

Repair and Maintenance Recommendations

• Replace cracked or aged hoses and tighten hose clamps.
  
• Rebuild or replace faulty water pumps and associated seals.
  
• Repair or replace damaged radiators and heater cores.
  
• Replace worn gaskets and freeze plugs with quality OEM parts.
  
• Flush and refill the cooling system with appropriate coolant mixture.
  

Operator Experiences and Case Studies
One operator noted a persistent coolant leak traced to a deteriorated lower radiator hose near the connection. Replacing the hose and tightening clamps resolved the issue immediately.
Another case involved a leaking water pump seal causing coolant loss without visible external dripping. Replacement of the water pump eliminated overheating and restored system integrity.
In a severe example, a blown head gasket allowed coolant into the combustion chamber, causing white smoke and engine misfire. After comprehensive repairs including gasket replacement and engine cleaning, the machine returned to reliable operation.

Terminology and Technical Notes

• Water Pump Seal: Prevents coolant from leaking where the water pump shaft exits the housing.
  
• Freeze Plug (Core Plug): Metal plugs in engine block to protect against freeze damage, which can corrode over time.
  
• Head Gasket: Seals the cylinder head to the engine block, maintaining compression and coolant containment.
  
• Pressure Tester: A tool to pressurize the cooling system to detect leaks.
  
• UV Dye Test: Technique using fluorescent dye and UV light to locate hard-to-see coolant leaks.
  

Maintenance Checklist to Prevent Coolant Leaks

• Inspect coolant hoses and clamps regularly for signs of wear.
  
• Monitor coolant levels daily to detect sudden drops.
  
• Schedule routine cooling system flushes and refills.
  
• Check water pump condition during engine service intervals.
  
• Pay attention to engine temperature readings and unusual exhaust smoke.
  

Conclusion
Coolant leaks in Cummins 855 engines can arise from multiple sources, but with careful inspection and maintenance, most leaks are preventable or repairable without major engine work. Operator vigilance and timely repairs help avoid costly downtime and ensure engine longevity. Combining traditional inspection methods with modern diagnostic tools like pressure testers and UV dye enhances detection accuracy.