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Old 08-06-2020, 12:07 PM   #1
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Turbo Diesels

Many posts mention turbo diesels that are pumped up to max hp are more likely to have issues at high engine hours. Agreed.

I've been around a lot of different types of boats. The multi million dollar sport fishers are typical for maxing out engines with turbos. These boats would idle for a good 1/2 hour after arriving to cool down the turbos and prevent turbo bearings from heat damage. That practice could be applied to trawlers as well with turbos.

Another thing that I've seen (unlikely to apply to trawlers) is custom 50' plus that can run at 40+ knots. They suck so much air that the engine hatch/steps in cockpit had to be opened 8 " to allow them to breath. Bad design but this can happen with billionaires who say to the builder, I don't care what it costs, make it faster than anyone else's boat.

Some folks have more dollars than sense. LOL.
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Old 08-06-2020, 12:37 PM   #2
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The damage caused by running a turbo diesel at near top hp is the excessive wearing away of the metals in the cylinders by high exhaust gas temperatures. Turbo bearings are usually cooled by engine oil. As long as the oil is properly cooled by the heat exchanger, the bearings shouldn't see excessive wear.

Idling after a run does more to cool down the exhaust piping and engineroom than saving turbo bearings. Forced ventilation does more to cool down the engineroom.
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Old 08-06-2020, 01:24 PM   #3
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Thanks for your comments. I'm repeating what the paid capt and crew had told me from the 80s for their specific boats. They said that the turbos bearings can coke with oil. Maybe you're talking about "in general" for most ideal situations. I don't think you're saying they are wrong. If I ever have turbo diesel, I intend to idle to aid cool down. I'd also avoid a max power turbo engine, on my don't buy list. I'll also add fresh water flush kit to any engine to prolong the life of intercoolers and exhaust.
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Old 08-06-2020, 01:28 PM   #4
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Sounds good.


Would argue the water cooled diesel engine needs little cool down before shutting down... probably the time it take to dock. And, yes the exhaust is the HOT part.


And the turbo bearings do get hot and hard to get them a whole lot cooler before the engine is shut down. The engine, itself, for the most part is a non issue. Not much worse than a NA engine.


However, overall, turbo'd engines do cost more to operate, typically burn more fuel (but get more power) and will die before the NA counterpart.



I'd rather not have a turbo, especially in a boat or car.
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Old 08-06-2020, 01:44 PM   #5
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Agreed SeeVee. Looking at two of thee same engines, one NA, the other turbo. I'd be OK purchasing with 6000 hours on NA, not the turbo, unless it had been totally rebuilt.
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Old 08-06-2020, 01:57 PM   #6
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Quote:
Originally Posted by Swfla View Post
Many posts mention turbo diesels that are pumped up to max hp are more likely to have issues at high engine hours. Agreed.

I've been around a lot of different types of boats. The multi million dollar sport fishers are typical for maxing out engines with turbos. These boats would idle for a good 1/2 hour after arriving to cool down the turbos and prevent turbo bearings from heat damage. That practice could be applied to trawlers as well with turbos.

Another thing that I've seen (unlikely to apply to trawlers) is custom 50' plus that can run at 40+ knots. They suck so much air that the engine hatch/steps in cockpit had to be opened 8 " to allow them to breath. Bad design but this can happen with billionaires who say to the builder, I don't care what it costs, make it faster than anyone else's boat.

Some folks have more dollars than sense. LOL.
A typical turbocharger has no bearing, only a journal with no moving parts to damage.
Newer designs do use ceramic bearings which are quite impervious to heat.

On many modern turbodiesel engines the turbocharger 'bearing' is also water-cooled.

In any case a lengthy post docking idle time will have little effect on longevity after
the boat has been throttled back during the harbor entrance to dockside run.

Old school organic based oil could oxidize in the journal of a hot turbo, running or not.
The use of synthetic oil blends now greatly reduce 'cooking' of the oil in the bearing.
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Old 08-06-2020, 01:58 PM   #7
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A lot depends on manufacturer, model, HP ratings. Have a Cummins 6BT 220 HP in my Dodge pickup. Getting ready to turn 10,000 hours (495,000 miles) on the original turbo, and it's not even liquid cooled.

Had the same engine in my charter boat before swapping for more HP. That 6BT 210 HP had a liquid (engine coolant) cooled turbo. With around 8,000 hours on it, the turbo showed no signs of wear. Change the oil regularly and don't run them continuously on the pin is a good recipe for long engine life.

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Old 08-06-2020, 02:10 PM   #8
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I always thought the cool down period was just to ensure oil feed to the turbo until it fully spooled down. Generally not an issue with boats.
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Old 08-06-2020, 02:13 PM   #9
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I'm so glad you posted about synthetic blend oils. Big difference from the situation of the boats I described back in the early 80s. Even if one were to have a turbo engine from that era. The new oils make a big difference. I also took time to view a youtube comparing the two types of turbos. Thanks for bringing my thinking to the 21st century!! I no longer am under the impression that a long idle will matter. Ideally, I'll end up with Ford Lehman NA or Cummins NA for power. But would be OK with light turbo boost. But that's another thread.
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Old 08-06-2020, 02:13 PM   #10
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With a water cooled turbo, a few seconds at idle is typically fine. For a non water cooled turbo, a minute or so for turbo temps to drop is a good idea. Typically the engine will be run gently for a couple of minutes before shutdown anyway, so it's only going to cool a little more at idle.
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Old 08-06-2020, 02:15 PM   #11
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Quote:
Originally Posted by O C Diver View Post
A lot depends on manufacturer, model, HP ratings. Have a Cummins 6BT 220 HP in my Dodge pickup. Getting ready to turn 10,000 hours (495,000 miles) on the original turbo, and it's not even liquid cooled.

Had the same engine in my charter boat before swapping for more HP. That 6BT 210 HP had a liquid (engine coolant) cooled turbo. With around 8,000 hours on it, the turbo showed no signs of wear. Change the oil regularly and don't run them continuously on the pin is a good recipe for long engine life.

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Old 08-06-2020, 02:17 PM   #12
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In general, turbo or not, longevity is dependent on engine design vs power output. Taking a design that's long lived at 200 hp and cranking it up to 400 is going to reduce lifespan. Headroom in the original design and any changes that can be made in the process will determine how big the reduction is, but it'll never live as long as a clean sheet design targeting 400hp.
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Old 08-06-2020, 02:35 PM   #13
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Makes sense. I wonder how many clean sheet designs exist of available trawler friendly turbo engines that target high hp.
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Old 08-06-2020, 02:45 PM   #14
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Yes typically the "bearings" are bronze bushings. You should let the tubo cool a little bit so the oil doesn't coke or burn onto the bearing surface. That will reduce clearance and eventually can cause failure.
I had a pyrometer (to monitor exhaust gas temperature) and would let the engine in my old Dodge/Cummins idle for about 45 second to 1 minute before the temp dropped to an acceptable level. If I was just pulling a hill, it would take a little longer to cool.

What typically kills a marine turbocharger is salt water intrusion from a poor exhaust design.
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Old 08-06-2020, 03:01 PM   #15
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Typically it's NOT the exhaust gas temperature that matters. Once the throttle is reduced the EGT reduces quite rapidly.



The head temp takes a bit longer to cool but not much with water cooling.



I'd bet that the bearing or bushing would be the critical thing in getting it cooled, which is most likely cooled somewhat by the oil, and when the engine stops, the oil pressure stops, too. Not much one can do about it, but not a huge deal it one just operates a short time at low rpm as their docking and would probably be fine.


FWIW, Yanmar calls it a bearing.... moot point.
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Old 08-06-2020, 03:09 PM   #16
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Yep, you have to call it something.

In most turbos, the oil itself performs the function of a bearing.
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Old 08-06-2020, 04:17 PM   #17
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Usually by the time you get docked the turbo has spun down and cooled enough that it doesnít need to sit at the dock idling. Unless you fun really hard right up to the dock and shutdown. In our case we are a half an hour up the no wake river to our dock.
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Old 08-06-2020, 04:49 PM   #18
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Only have experience at the other end of spectrum. Low horsepower engines. Have run boats with natural, turbo and turbo/common rail. Would think trawlers are more like sailboats. Both are full displacement vessels. You get up to hull speed or near hull speed and thatís it. Issue commonly is to get enough load on them. My experience has been running at 2/3 to 3/4 peak rpm with sufficient load is the sweet spot. Best mpg and best for the engine. Would think for trawlers having an exhaust temperature guage and a variable pitch prop so engine was running at its ďconstant runningĒ parameters would be more important than other things. Have had to clean my turbo but thatís it. Used to crew on occasion for a friend with a commercial trawler. Had a Gardner 3+3 older than me. He took one day off a week as long as he wasnít iced in. Think dissimilar metals with different coefficients of expansion, inadequate cooling, not enough oil changes, black box misprogramming and such issues are the causes of short engine life.
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Old 08-06-2020, 05:15 PM   #19
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So for those of us that run at typical displacement speeds, how hot are the turbos going to actually get? My engine is turbocharged, but at the load that I run it at, it is producing very little boost.
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Old 08-06-2020, 05:15 PM   #20
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There are a lot of broad brush strokes going on here. I will say that.....it depends. Someone said that doubling the power of the same basic block will dminish longevity. That is not necessarily the case. It will diminish longevity if that exrtra power is used. If it is not, then it will last just as long as the NA counterpart....assuming proper mtx. A 671 Detroit is a good example. NA that engine is somewhere around 260hp. The most pumped up version I have seen is 485hp. That 671 will go 30,000 hours if run gently....regardless of turbo or not. Now if you have that 485hp version in a Post 46 Sportfish and you run it on the pins all the time, it is a 2500 hour engine.

The OP said he would go with an NA version of a Cummins. I will say good luck with that! I know they are out there but they are extremely rare. The 6B block is almost exactly the same displacement of the Ford Lehman. ANd not so coincidently, the NA version in a pleasure boat application is 115hp. The more common engine is the 6BT at around 210hp. THe newer CPLs are 220hp. This engine has a turbocharger only with no coolers except maybe a transmission cooler. So it has the same basic mtx requirements as a Lehman. And run easily in a trawler application, is a solid 10?...20?...30,000 hour engine. So don't freak out just because it has a turbo. Now that same 5.9 displacement mechanical engine goes all the way to 370hp. If you run it hard, it won't last as long. But if you ran it the same way you ran that 6BT210hp engine, it would last just as long....and yes, a little more mtx with the aftercoolers and the fuel coolers. As a point of interest, Cummins has squeezed 480hp at of that same 5.9 liter displacement engine with their electronic common rail engines....crazy. But it shows how well Cummins builds engines. Sadly, the latest common rail B series(QSB)engines (de)rated to around 220hp still have aftercoolers....so that is a failure point and a very important mtx point.

Almost all new engines these days that will be in trawlers will be turbocharged due to polution laws. John Deere makes some good ones. Lugger....which is John Deere but a different marinizer. Cummins. I don't know the smallest engine Cat makes now. But their NA version of the old 3208 is a great engine(210hp)....albeit a giant engine. Volvo. Yanmar is going to be turbocharged and small and high revving. Don't believe the huyp about high revving engines. They can last too. If you ever see a water taxi in places like Vancouver, ask what engines they have. Likely Yanmar(because I asked). And 30-50,000 hours....granted they don't suffer age related breakdowns as they are running 6-10 hours a day 7 days a week and getting professional mtx.

Which brings up another issue.....AGE!!!! Don't rate an engines longevity on hours alone. Age can kill an engine as well if not kept up. Age meaning rust....turbos....coolers....all of these have a life span....and it isn't 40 years like the age of the Lehman. But some people blindly plod along with coolers(trans,oil,HX,etc) that are WAY over their lifespan and their failure could have catastrophic results regardless of how many hours are on the engine. It is due to age...not wear.

Ok...thasall for now!!!
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