Expensive Main Engine Damage Due to Defective Outlet Diaphragm



The vessel had completed a scheduled drydocking. After departing from the drydock, the vessel experienced extensive water ingress at various locations, which led to excessive water accumulation on the tank top. The leaks were repaired and completed. The following day, an unusual noise was heard from cylinder unit 4. The main engine was stopped and the crankcase was opened. An inspection of the unit revealed problems that could not be rectified immediately. Cylinder unit 4 was isolated. Without any rectification, the main engine was restarted and the voyage resumed. Shortly afterward, a loud noise was heard from the main engine and the exhaust gas temperature of cylinder unit 8 was slowly falling. So, it was decided to stop the main engine for further investigation. Several fuel injection valves and fuel pumps were changed. After several starting attempts, the engine was finally restarted.

Investigation Results:

  • Investigations proved extensive damage to
    • The main bearings
    • Big end bearings
    • Cross-head bearings
    • Piston rods
    • Piston crowns 
    • Exhaust valves
  • Two of the three rubber diaphragms on the crankcase oil outlets were defective.
  • The system oil was contaminated with 2% water.

Reason Explained:

Water from the tank top had entered the main engine sump tank through the two defective diaphragms and it contaminated the lubrication oil. A water content higher than 1% could lead to critical damage within a few days of operation. If the oil system is contaminated by an amount of water exceeding the limit of 0.2 to 0.3%, the engine manufacturer or “The Problem-Solving Lab – Viswa Lab” should be contacted. This contamination could cause:

  • Surface corrosion
  • Increased component wear
  • Jamming of components
  • Reduced load bearing capability and other in-direct impacts


The damage to the main engine was extensive and expensive. The repair cost for this type of engine damage can easily reach millions of dollars.

Lesson learned:

  • The diaphragm sealing of the crankcase oil outlet must be inspected regularly.
  • The diaphragm must be replaced for every 32,000 hours of operation.
  • The cost of an inspection/replacement is minimal compared to the consequences if left unattended.
  • Sufficient oil should be kept onboard for one complete system change of the main engine crank-case oil.

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SourceThe Swedish Club 


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