reconditioned turbo

[chris66]

i lost power recently on the starboard engine (volvo tamd 260c - 1200 hours) and a failed turbo was diagnosed. My mechanic took it to get reconditioned and €900 later there it was. 18 hours later it goes again. The reconditioner came on board to look at it and said that it was undoubtedly due to changes in oil pressure during use and so not his fault and so he won't redo it again. In fact to prove his point he will take the boat out for "an extended sea trial" with my mechanic to prove his point.

Now my (south african) mechanic doesn't believe that there is a problem with the oil presure but has a little difficulty in conversing with the French turbo man.

Anyway, how much truth could there be in what the turbo man says and what, if anything, should I ask my mechanic to take a special look at prior to this sea trial to make sure it doesn't cost me another €900 odd.....

Thanks
Chris


<hr width=100% size=1>Chris

 

[William_H]

Turbo chargers suffer from excessive heat. They are in some cases water cooled but mostly are oil cooled by the oil pressure to the centre bearing. They get very hot under high power conditions and when you shut down thebearings often get even hotter before starting to cool. The problems often arise from the oil being overheated and becoming abrasive carbon. Hence the need to cool down turbos. (Helicopters are a real problem as they run near full power until they are on the ground most idle for at least 5 mins before shut down.) So problems are usually caused by rapid temperature change and not leaving idle long enough to stabilise temperature while maintaining oil flow to bearings. If your engine was tired and oil pressure at idle very low then there could conceivably be turbo damage when you idle for cool down . I often wonder why an additional electric oil pump is not provided so that oil flow can be maintained after engine shut down for a period. You would still need to stabilise temperature for a time after high power anyway. Many modern diesel vehicles have a delayed shut down for this reason. You will see an owner lock up and walk away from a vehicle with engine still running. So I probably havn't said anything you didn't know but it may help. good luck will

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[Ships_Cat]

I agree with William, there is a possibility that the turbo guy is correct. I can add to William's comments by saying that sometimes oil passages to the turbo bearings can get restricted with sediment as well.

But turbos are generally prone to problems (I was recently involved with a new quality V8 marine diesel received from the factory to go into a new build which had suffered turbo damage during the factory tests - was discovered in the yard before the engine had even been installed in the boat).

Another difficulty is sustained operation at high load resulting in high exhaust gas temperatures, but this can be measured if you have an exhaust gas temperature measurement sensor installed - most pleasure marine diesels are highly rated (the similar engine sold for commercial use will be down rated) and once they operate past their maximum torque output, exhaust temperatures may rise. This not only may result in turbo damage but also valve and head damage, and damage to components such as exhaust manifold diffusers, etc should they be fitted. This problem is also common in diesel non commercial pleasure road vehicles (eg 4x4's) frequently used for heavy loads (so it is perhaps fortunate that most of them are only used to do the shopping and dropping the kids to school).

So, without knowing much about the details of your problem, it would seem that the sea trial with an open mind to cause is the only solution. Bear in mind that the other engine will have been operating under the same life conditions and may also be prone to the same failure so there is some incentive in identifying the real problem rather than just trying to show the fault for the second failure of the turbo is the turbo guy's.

John

<hr width=100% size=1>I am the cat but I am only 6.

 

[brianhumber]

I would agree with William and Ships Cat points.
Small turbos run very hot on full load ( some of the older less efficient casings would run white hot under full chat so you can see how stressed the rest of the manifolds get) and why good cooling is essential.
If the turbo is run beyond its design then the excess heat will cause problems as the work balance between the energy in exhaust gases cannot match what is needed to compress the air side. I would also carefully get checked the air side as well as any restriction will result the air compressor being unable to use the available energy in the exhaust gases and it will tend to run hotter.
Turbo fitted engines are fascinating things but can be difficult. Good instrumentation is essential for dianosis as todays turbos are designed to work under close tolerances and a small 'sweet spot' Good luck

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