Cylinder Head Studs Broke Due To Cooling Water Ingress!


Cylinder head studs play a vital role in transmitting the combustion forces onto the engine structures and entablature.  This case study is very interesting and it throw lights on how a cooling water leak can lead to failure of cylinder head studs.

Main Engine : 12 RTA 96 C
Running Hours : 68,590
Power : 63,000 kW @ 100 rpm
Vessel : Containership

A vessel experienced frequent failure of cylinder head studs and the ship staff continue to replace it with new studs every time.  Though many attempted to find out the root cause of the failure, they were not successful in finding out the root cause of the problem.  As the cylinder head studs failed, there was a subsequent failure of piston rings and at worst case, cylinder liners were getting worn off.

The engine expert advice was sought after to find out the root cause.

Work Done:

  1. Overhaul of unit #10 piston with new piston rings.
  2. Unit # 4 cylinder liner replacement.
  3. Broken Cylinder head studs removal in two units.

Piston being overhauled!



Under Piston Space – Cleaned & Inspected



New Liner – Lubricating Quills being Checked for its Proper Operation


Broken Cylinder Head studs being removed


Broken Cylinder Head studs being removed


At Last – This man successfully removed the broken stud after  6 hours of struggle!


Root Cause:

The o-rings and gaskets in the cooling water outlet pipe were not properly installed which lead to minor cooling water leaks in various units.  The main reason was corrosion pitting caused by leaking cooling water that is collected on the engine entablature.  The leaked cooling water seeps into the threaded area of the cylinder stud.  This creates a corrosion pitting and is a weak point a so-called notch effect that starts a slow fatigue crack and finally results in a complete failure after many hours of service, even such a heavy stud breaks.  The cure is to avoid leaking cooling water on the entablature and to seal the threaded area with silicone or other engine maker recommended sealant to be extra safe if cooling water should accidently leak.

About the Author:

t_ADED2632-6271-1048-CE1C-C5647005C452.jpgMr. Holger Jacobsen, the “Engine Expert” has spent over 23 years with MAN Diesel & Turbo, managing both field and technical services in Australia and Singapore.  He was the Head of Diesel Engineering at Teekay Shipping in Vancouver BC.  In 2009, he started the Emission Services for Wartsila in Canada and has been with Wartsila for 6 years.  With both MAN Diesel & Turbo and Wartsila’s tag over his name, he has a ‘Midas touch’ to solve/consult on any diesel engine problem.  With over 30 years of working experience on diesel engines of any size/make,  We honour him with the title – the “Engine Expert”.

Write to Holger through MFAME.

Do you Have an Engine Problem? Write to Holger at:


  1. Hi Found the article on broken studs very useful. Would like to receive newsletters and to have any queries addressed. Many thanks

  2. On some new engines, as additional safety a seal ring is provided on cylinder head studs, that should seal against water entering in narrow space between screw threads. However, with time, seal rings age, and deteriorate. It is still advisable to use the sealant on top. Periodically the sealant may detach due to dryness etc. This should be renewed after cleaning.
    Many engineers neglect such leaks, on engine entablatures as it happens on and off, from cooling pipes between the jacket and cylinder cover, or other sources.

  3. We have the following engine on board our MT Alfa-007 ( IMO # 9182095 )

    Main Engine :

    MODEL 5L35MC
    SERIAL # 5191
    MAX OUT PUT : 4.400 BHP @ 210 RPM
    NO. CYL : 5

    We bought this vessel in 2019 from Turkish owner.

    In 2015 we started to have problems w/ the cylinder head stud bolts, they started to break, we found excessive corrosion due to water leakage (seems that these were the original bolts from built), so we stared to change all the bolts one by one. Finally we changed 100% of the w/ new MAN Stud Bolts and we did some correction on the liners to prevent water leakage. We did uses silicon paste to prevent water from coming in.

    The other day one of the bolts from cylinder # 2 broke ( se picture ) , the broken parts does not seems corroded. This Stud Bolt only has 6.000 running hours.
    We are going to send the two parts of the bolts to a LAB to analyze the type of fracture.

    Some info that might help to get to the problem :
    • The Main Engine runs aprox 210-250 hrs per month.
    • We use MDO instead of IFO180
    • Every month we start & Stop the engine aprox 420-440 times, this means fwd and aft. ( that’s a lot of maneuvers )
    • The bolt broke during navigation

    What could be the problem….?


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