Oil Leaking from Exhaust Ports on Cummins NT855: Troubleshooting and Solutions

[MikePhua]

Introduction
Oil leaking from the exhaust ports of a Cummins NT855 engine is a concerning issue that can affect the performance and longevity of the engine. This type of problem often indicates an underlying issue within the engine’s internal components, particularly the valve seals, turbocharger, or cylinder head gasket. In this article, we will explore the common causes of oil leaks from exhaust ports, potential solutions, and steps to troubleshoot this issue effectively.
Understanding the Issue
The Cummins NT855 is a heavy-duty engine used in various industrial and agricultural applications. Its robust design ensures reliability and power, but like any engine, it can face certain issues over time. One of the more perplexing problems is oil leaking from the exhaust ports, which can lead to excessive smoke, loss of power, and other mechanical failures.
Common Causes of Oil Leaks from Exhaust Ports

1. Worn Valve Seals or Guides
   One of the most common causes of oil leakage through the exhaust ports in the NT855 is worn or damaged valve seals or valve guides. These components are responsible for preventing oil from entering the combustion chamber. Over time, valve seals can wear out, allowing oil to seep into the exhaust ports during the exhaust stroke. This can result in visible smoke from the exhaust and a loss of engine efficiency.
   
2. Turbocharger Issues
   The turbocharger plays a crucial role in the performance of the NT855 engine by boosting the intake air pressure. If the turbocharger seals become worn or damaged, oil can leak into the exhaust system. This can cause oil to burn off, leading to oil residue accumulating at the exhaust ports. Regular inspection of the turbocharger seals and oil lines is necessary to prevent this issue.
   
3. Blown Head Gasket
   A blown head gasket is another possible cause of oil leaks from the exhaust ports. The head gasket seals the engine block and cylinder head, preventing the mixing of oil and coolant. If the gasket fails, oil can leak into the exhaust ports, causing burning oil to escape through the exhaust system. This issue may also cause overheating and engine misfires, so it is crucial to address it promptly.
   
4. Cylinder Wear or Piston Ring Failure
   Another potential cause of oil leaking through the exhaust ports is excessive cylinder wear or damaged piston rings. When the piston rings become worn or damaged, oil can enter the combustion chamber, where it burns and exits through the exhaust. This condition often results in significant smoke, a decrease in engine power, and increased oil consumption.
   
5. Excessive Engine Oil Pressure
   If the engine oil pressure is too high, it can force oil into the exhaust ports. This can happen if the oil pressure relief valve malfunctions or if the oil is overfilled. High oil pressure can cause oil to leak past the valve seals or other engine components, leading to oil accumulating in the exhaust system.
   

Symptoms to Look For
If you suspect oil is leaking from the exhaust ports of your Cummins NT855 engine, look for the following signs:

• Blue Smoke from Exhaust: One of the most noticeable signs of oil leaking into the exhaust ports is blue smoke coming from the exhaust pipe. This occurs because the oil is burning off as it escapes through the exhaust system.
  
• Increased Oil Consumption: If the engine is burning more oil than usual, it could indicate an oil leak from the exhaust ports or elsewhere in the engine.
  
• Loss of Power: As oil enters the combustion chamber, it can cause poor combustion and reduced engine performance. If the engine is losing power, this could be a result of oil contamination.
  
• Oil Residue on Exhaust Components: Visually inspect the exhaust ports and surrounding components for oil residue or deposits, which can be a clear indicator of oil leakage.
  

Troubleshooting Steps

1. Check the Valve Seals and Guides
   Inspect the valve seals and guides for wear or damage. If the valve seals are found to be faulty, replace them to prevent further oil leakage. This may also involve inspecting the valve guides for any irregularities that could allow oil to seep past them.
   
2. Inspect the Turbocharger
   Inspect the turbocharger for signs of oil leakage. This can include checking the seals and oil lines for any signs of wear or cracks. If the turbocharger is the cause, replace the seals or rebuild the turbocharger as needed.
   
3. Examine the Head Gasket
   Perform a compression test or coolant pressure test to check for a blown head gasket. If the gasket is blown, it will need to be replaced. This is a more involved repair that may require removing the cylinder head.
   
4. Inspect the Piston Rings and Cylinders
   Perform a cylinder compression test to check for signs of excessive wear on the piston rings or cylinders. If the test shows low compression, this could indicate piston ring failure or cylinder wear, both of which can cause oil to leak into the exhaust system.
   
5. Check Oil Pressure
   Ensure that the oil pressure is within the recommended range. If the oil pressure is too high, investigate the oil pressure relief valve and adjust the oil levels to the correct amount.
   

Preventive Maintenance
To reduce the risk of oil leaks from the exhaust ports, regular preventive maintenance is essential. Here are some tips:

• Regular Oil Changes: Change the engine oil at the recommended intervals to ensure proper lubrication and reduce the risk of excessive wear on engine components.
  
• Monitor Oil Levels: Always ensure that the oil is at the correct level and never overfill. Excess oil can lead to increased pressure and cause leaks.
  
• Inspect the Turbocharger: Regularly inspect the turbocharger for oil leaks and wear. Clean and maintain the turbocharger to prevent oil from entering the exhaust system.
  
• Check Valve Seals and Guides: Keep an eye on the condition of the valve seals and guides. Replace them as needed to prevent oil from entering the exhaust ports.
  

Conclusion
Oil leaks from the exhaust ports on the Cummins NT855 engine can be caused by several issues, including worn valve seals, turbocharger problems, a blown head gasket, piston ring failure, or excessive oil pressure. It’s crucial to diagnose and address these problems promptly to avoid further engine damage. By performing regular maintenance and conducting thorough inspections, you can extend the life of your NT855 engine and keep it running smoothly.