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Old 05-04-2014, 12:38   #46
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Re: Turbo vs normally aspirated

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Originally Posted by jtsailjt View Post
I'm a new owner of a remanufactured 88hp yanmar turbo diesel and the guidance I can find regarding frequency of turbo washing ranges from 150 to 600 hours. Does your manual really say weekly? Did you mean weekly if run 24 hours a day? What do other yanmar turbo owners say about how often they recommend turbo washing assuming normal use?

All diesels like to be run around 80% power for the majority of the time, nothing different about a turbo versus NA diesel there. Whether or not you have a NA or turbo diesel, you'll still be operating it at low power settings at startup and approaching the slip. But since having a NA engine will mean it's bigger than an equivalent HP turbo engine, you'll be running a bigger engine at lower power settings during this period.

As I mentioned earlier, I'm not experienced at running a turbo but it seems to me that at least a few minutes of low power warmup and warm down of the engine, during which nothing is being demanded of the turbo would be a good thing to allow for good lubrication and gradual warmup and to dissipate excess heat before shutdown. Am I wrong?

You're absolutely right, for the longest life from a TD engine letting it warm up and cool down is an excellent practice to follow. The warmup period is to allow the block, cylinder head gasket and cylinder head(s) to all come up to temp. and seal properly before a load is placed on them, and the cool down period keeps oil flowing to the still hot turbo bushings or bearings and helps cool them down and prevent coking.
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Old 05-04-2014, 13:23   #47
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Re: Turbo vs normally aspirated

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Originally Posted by Horror Hotel View Post
Making 60 hp requires the same fuel whether NA or turbo.
Not quite true. Specific power (amount of fuel required to produce a given amount of kwH or horsepower/hours) is improved by turbocharging, usually by about 10% but can be more. That is because energy from the exhaust stream which would otherwise be wasted in a NA engine is recaptured by the turbine, and because efficiency of the combustion process is somewhat improved.

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"Fuel consumption values of two medium-speed diesel engines of equal horsepower with (solid curves) and without(dash curves) turbocharging, showing significant advantages for the tur-bocharged engine [5].aspirated engine.Downsized engines, for a desired power output, present smaller brakespecific fuel consumption values, Figure 5.7." Turbocharged Engines | Patric Figueiredo - Academia.edu


And some turbocharged engines are more efficient than others. For example, the Yanmar 4JH3-HTE with intercooler uses less than 160 grams of fuel per horsepower/hour over a wide range of speeds; and 153 at 2500 RPM.

The 4JH3-TE, which is the same engine but without the intercooler, has best specific consumption of 167 grams/horsepower/hour. That is, about 9% more fuel consumption for a given power output, just because of the lack of an intercooler.

I couldn't find the specific fuel consumption curves for the Perkins M4.236, but we can be sure that there's a pretty big difference to the 4JH3-HTE. The big naturally aspirated Perkins has much bigger cylinders to give the same amount of power (actually a bit less). The greater area of those bigger cylinders will mean more heat energy is lost to the cooling system, rather than being converted to mechanical energy. Those bigger cylinders will produce more friction. None of the energy of the exhaust stream is recaptured.

I would be bet that the 4JH3-HTE is 9% more efficient than the also turbocharged 4JH3-TE, then it must be 20% more efficient than the Perkins if not more.


A different question is whether or not we care -- maybe we sailors don't care that much about +/- 20% of fuel consumption, since long passages will always being done under sail anyway. Fair enough.

On smaller engines (Under 80 horsepower? Under 50?) it may also not be worth thinking about. Everyone will have to decide for himself, but turbocharged engines are more efficient; that's just a fact.

For me, I don't think 20% difference in fuel consumption is a big factor. For me, the main advantage of a modern turbo-diesel is weight and size. Weight makes a big difference to sailing performance. The Yanmar with reduction gear weighs 256 kilos; the Perkins at 520 kg is more than double the weight! 264 kilos of difference or 580 pounds! Wow! That's a quarter of a ton of difference!

To put it another way -- the 100 horsepower Yanmar plus my heavy-duty, continuous-duty rated 6.5EFOZ Kohler genset together with sound enclosure together weigh about the same as a Perkins M4.236 of 85 horsepower.

For many sailors, that alone will be well worth the added complexity of a turbocharger.
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Old 05-04-2014, 14:05   #48
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Re: Turbo vs normally aspirated

Wash every two weeks?

I have a five year old Yanmar 4JH4-HTE (turbo with intercooler) with 1300 hours and the turbo has never been washed (or given a bit of trouble).

Where did you see the two week recommendation? My mechanic (very good) laughts at the 250 hour recommendation in the manual. The manual also has a mandatory replacement of the exhaust elbow before now that makes him chuckle. The elbow was still great when last pulled at 1000 hours (I do carry a spare).

Even though I love to sail, I make sure I have an hour or two of good hard engine running every few days when cruising. I consider it required maintenence. My mechanic says that's probably why my exhaust elbow and turbo have lasted so well.

That and I'm religious about oil and coolant changes.
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Old 05-04-2014, 16:53   #49
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Re: Turbo vs normally aspirated

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Originally Posted by CarlF View Post
Wash every two weeks?

I have a five year old Yanmar 4JH4-HTE (turbo with intercooler) with 1300 hours and the turbo has never been washed (or given a bit of trouble).

Where did you see the two week recommendation? My mechanic (very good) laughts at the 250 hour recommendation in the manual. The manual also has a mandatory replacement of the exhaust elbow before now that makes him chuckle. The elbow was still great when last pulled at 1000 hours (I do carry a spare).

Even though I love to sail, I make sure I have an hour or two of good hard engine running every few days when cruising. I consider it required maintenence. My mechanic says that's probably why my exhaust elbow and turbo have lasted so well.

That and I'm religious about oil and coolant changes.
Good for you. Coolant changes are one of the most neglected items of diesel engine maintenance.


My maintenance regime is exactly the same as yours, including the periodic hard running.

I like to get in a few minutes of full revs every time I anchor -- I always back down at full power for a few minutes.

As to washing the turbo -- I did this (with the horridly expensive Yanmar turbo wash liquid) two years ago at about 1200 hours, but the turbo was not dirty. Never had the slightest problem with my turbo either.



I have had other problems with my Yanmar, but one thing I really like about it is that it does not leak a single drop (and that's not hyperbole) of either oil or coolant. Probably the first engine I've ever had like that, in a lifetime of owning hundreds of internal combustion engines.
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Old 06-04-2014, 07:42   #50
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Re: Turbo vs normally aspirated

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......but one thing I really like about it is that it does not leak a single drop (and that's not hyperbole) of either oil or coolant. Probably the first engine I've ever had like that, in a lifetime of owning hundreds of internal combustion engines. Knock on wood.
I agree and I've had the same experience with yanmars but the way you stated it made me too nervous!
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