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Old 02-11-2015, 18:56   #16
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Re: Light Loading of Diesels -- How Harmful?

Dockhead,

Disclaimer: Maybe you should talk to a knowledgeable diesel engine tech.

Years ago when I worked on a farm when we had a turbo diesel that started making billowing white smoke the first suspect was the turbo. Insufficient air pressure prevents full combustion of the fuel and that makes lots of white smoke in the exhaust. It could also be some kind of low throttle error causing too much fuel to be injected I suppose. But lots of billowing white smoke means something is wrong.
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Old 02-11-2015, 21:57   #17
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Re: Light Loading of Diesels -- How Harmful?

Quote:
Originally Posted by a64pilot View Post
Funny thing about the Mil test was that 60KW and larger generators had load banks on them, great big resistance heaters to load the engine when it wasn't being used to run an electrical system or something.
But Yanmars have the reputation of being smoky, mine nasties up the transom, I hope that will go away now that I had all the nozzle tips replaced, but they are I believe not known to be clean burning engines.


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I have this same issue with my 4JH4-TE in my boat. Brand new last year, and started it first time early summer. I pin it to win it when breaking it in at the proper intervals and when I do, I hit hull speed and then some. The transom squats and when I get in to dock I have a soot line on the transom. It doesn't have white or black smoke at any point of rpm or load. I figured it was just due to break in.. I have a Vetus horizontal muffler and a Vetus goodneck all in 3in. Barely hear the thing running on my boat. Good to know it's just a sooty engine.

But Yea, fires up as soon as I push the button, just awesome!

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Old 03-11-2015, 02:05   #18
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Re: Light Loading of Diesels -- How Harmful?

Sounds like you might not be getting enough air through the engine. The turbo bearings might be worn this will cause similar smokeing. Also sometimes the intercooler can get partially blocked from oil leaking through the turbo bearings. Old or incorrect engine oil can cause the turbo to spool up slower and cause smoke. Not enough air into engine compartment can also cause this.
Not getting air out through too much exhaust backpressure can also cause similar problem.

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Old 03-11-2015, 07:50   #19
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Re: Light Loading of Diesels -- How Harmful?

Quote:
Originally Posted by Sardean View Post
Sounds like you might not be getting enough air through the engine. The turbo bearings might be worn this will cause similar smokeing. Also sometimes the intercooler can get partially blocked from oil leaking through the turbo bearings. Old or incorrect engine oil can cause the turbo to spool up slower and cause smoke. Not enough air into engine compartment can also cause this.
Not getting air out through too much exhaust backpressure can also cause similar problem.

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I wonder if exhaust back pressure has something to do with it . we need to hear from someone with a very short exhaust track . My engine is in the middle of the boat being a center cockpit , as it is in the Moody's as well . I have two risers , one in the engine room right out of the water lock muffler and one at the transom . Seems like a lot of vertical water column to get the exhaust through. when I installed the generator i just put in a single riser right out of the water lock muffler beside the engine , then straight out the transom . It is a longer way because the generator is forward of the main engine . But i get no smoke at all . white or black .

Maybe the turbo engines are sensitive to exhaust pressure , this spec must be available , but how to measure ? I know that the way exhaust travels inside a tube on a sloop with water is a very complicated dynamic interaction but there must be a spec for it.

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Old 03-11-2015, 08:15   #20
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Re: Light Loading of Diesels -- How Harmful?

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Originally Posted by a64pilot View Post
Aircraft, older cars when they had carburetors ran their air over the exhaust manifold to heat it and prevent carburetor ice.
But the rest of the world is going for cold air induction as the colder the air, the more dense. And if you have a turbo, trust me, the intake charge is well heated, trying to cool it down is what an intercooler is all about.


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I seem to agree with a65pilot all the time. I will add here that there needs to be some load or higher than idle rpm for the turbo to add manifold pressure and without added pressure the intake air temp is not heated.
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Old 03-11-2015, 09:49   #21
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Re: Light Loading of Diesels -- How Harmful?

I wouldn't worry about it. I've had that with 671s the smoke that goes away. I would imagine the fuel is coming in faster that it is being used while the RPMs come up.
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Old 03-11-2015, 10:24   #22
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Re: Light Loading of Diesels -- How Harmful?

I often worry about light loading. Over the years I've picked up several bits of advice that I now practice but don't know if any of it is urban legend. Should I stop any of these?

- On starting cold (Yanmar with turbo) after a minute to be sure oil pressure is completely distributed, I will run at 1200rpm for a few minutes and then 1400-1600 rpm until the water temperature gets to at least 160 degrees (less than 10 minutes). I'll then reduce RPM but keep the temp above 160.

- Every six-eight hours of operation I will run under load for 15 minutes at 90%+ RPM

- When shutting down after a long slow speed run into the dock, I advance the throttles to the stops in neutral three quick times then wait 60 seconds at idle before shutdown. (This was recommended by a Mack Boring expert)

I get virtually no smoke.
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Old 03-11-2015, 10:43   #23
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Re: Light Loading of Diesels -- How Harmful?

When used on canals at low speed it has always been the case that diesels suffer from glazed bores and smoke a lot on start up. They continue to smoke whilst running but a lot less. Look at a boat with an old DAF, Perkins or Ford. They all smoke but do not use oil. We are talking blue smoke here which is oil based. Black smoke is too much fuel.
These engines are 30, 40, and 50 years old, like to smoke and last forever!
Don't worry about it. It can be a bit antisocial though!
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Old 03-11-2015, 11:04   #24
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Re: Light Loading of Diesels -- How Harmful?

No matter what it is from a lawnmower to a several thousand HP Turbines, I have always been of the opinion to warm one up slowly and cool it off before shutdown, Army requirement for turbine is two min at idle. This lets things cool down and temps stabilize.
Especially important for turbos as they are usually oil cooled and get very hot, shut them down hot and you will form coke in the center section which will eat out the center section bearing, then the turbo "pinwheel" will make contact with it's housing and the turbo is no more.
Many small truck Diesel turbos are now water cooled to prevent this as Joe Public just won't be bothered with an idle cool down, don't know about boat motors.

Way we normally operate a boat motor is fine, I know whether docking or anchoring mine has a couple of min of idle time before shutdown, I do "set" the anchor, but don't use full throttle.
Turbo motors do require a little more care than their NA brothers
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Old 03-11-2015, 11:28   #25
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Re: Light Loading of Diesels -- How Harmful?

Quote:
Originally Posted by Pauls View Post
Well, actually you do a bit. Although the turbo isn't making any boost, as you say, the intake air is still going thru the aftercooler and so any attempt to heat the intake air (to improve the light loading combustion) would be negated by the aftercooler. It's hard to provide hot air to the engine when there's a cooler installed in the intake tract.

If you were of an experimental frame of mind it might be interesting to disconnect the aftercooler water lines, provide a source of hotter intake air, and see how this affects the lightly loaded running condition of your engine. I would expect it to run cleaner.

PS - I got into engineering originally because I was building racing engines and wanted a better grasp of the theory behind engine dynamics and design. I do understand high horsepower. I have a bike in the garage that runs mid 11's and is a ball on a twisty road. I bet you had a lot of fun with your 930. Sweet cars.
Thanks -- very interesting observations and I stand corrected.

Makes me think that it would be cool if you could switch the aftercooler from sea to fresh water -- which would HEAT the intake charge at zero boost, rather than cooling it.

But I will take A64's advice and simply avoid this fast idling.

As to the 930 -- yes, I loved it. But I loved more, the three early 2.2 liter 911S's I had over more than three decades. So light and athletic, and the engine made such a gorgeous shriek at its 7300 RPM redline. The 930 was a bit of a blunt instrument in comparison. I sold my last 911S just a few months ago -- to pay for new sails. Now I'm going through withdrawal, and I'm looking at a Lotus Elise S as a possible substitute. Not air cooled, not a six, but redlines at over 8000, engine behind you where it belongs, and light as sin, even lighter than the 911S. And dirt cheap. Hmmm. Just can't carry sails or buckets of antifoul in it

I gave up bikes after my third accident. The last one was a Ducati. I'm not a good enough driver, I guess, to ride motorcycles and hope to live to pension age . I'm much better with boats Be careful out there!
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Old 03-11-2015, 11:34   #26
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Re: Light Loading of Diesels -- How Harmful?

Quote:
Originally Posted by a64pilot View Post
No matter what it is from a lawnmower to a several thousand HP Turbines, I have always been of the opinion to warm one up slowly and cool it off before shutdown, Army requirement for turbine is two min at idle. This lets things cool down and temps stabilize.
Especially important for turbos as they are usually oil cooled and get very hot, shut them down hot and you will form coke in the center section which will eat out the center section bearing, then the turbo "pinwheel" will make contact with it's housing and the turbo is no more.
Many small truck Diesel turbos are now water cooled to prevent this as Joe Public just won't be bothered with an idle cool down, don't know about boat motors.

Way we normally operate a boat motor is fine, I know whether docking or anchoring mine has a couple of min of idle time before shutdown, I do "set" the anchor, but don't use full throttle.
Turbo motors do require a little more care than their NA brothers
Just like my father taught me. I also follow this practice.

I would prefer not to reveal, however, how long it took me to realize that diesels don't warm up at idle
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Old 03-11-2015, 11:36   #27
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Re: Light Loading of Diesels -- How Harmful?

Quote:
Originally Posted by typhoon View Post
I wonder if exhaust back pressure has something to do with it . we need to hear from someone with a very short exhaust track . My engine is in the middle of the boat being a center cockpit , as it is in the Moody's as well . I have two risers , one in the engine room right out of the water lock muffler and one at the transom . Seems like a lot of vertical water column to get the exhaust through. when I installed the generator i just put in a single riser right out of the water lock muffler beside the engine , then straight out the transom . It is a longer way because the generator is forward of the main engine . But i get no smoke at all . white or black .

Maybe the turbo engines are sensitive to exhaust pressure , this spec must be available , but how to measure ? I know that the way exhaust travels inside a tube on a sloop with water is a very complicated dynamic interaction but there must be a spec for it.

Regards
Interesting idea. But in my case -- there's a water separator, so no double lifting of water for the exhaust to do.
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Old 03-11-2015, 11:37   #28
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Re: Light Loading of Diesels -- How Harmful?

Quote:
Originally Posted by a64pilot View Post
No matter what it is from a lawnmower to a several thousand HP Turbines, I have always been of the opinion to warm one up slowly and cool it off before shutdown,

Well I know that you know that a turbine reaches it's highest temp during a start. Not much need to warm it up after that.
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Old 03-11-2015, 11:37   #29
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Re: Light Loading of Diesels -- How Harmful?

I've had three Yammers, including the model in this thread, and none have smoked except for a few white puffs during startup.
I always run them at 80% of WOT as suggested in the manual except when docking.
I always put them in Reverse when sailing as suggested in the manual.
All have run flawlessly.
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Old 03-11-2015, 11:43   #30
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Re: Light Loading of Diesels -- How Harmful?

Quote:
Originally Posted by Sardean View Post
Sounds like you might not be getting enough air through the engine. The turbo bearings might be worn this will cause similar smokeing. Also sometimes the intercooler can get partially blocked from oil leaking through the turbo bearings. Old or incorrect engine oil can cause the turbo to spool up slower and cause smoke. Not enough air into engine compartment can also cause this.
Not getting air out through too much exhaust backpressure can also cause similar problem.

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Yes! A dirty intercooler was the last thing on my list, and earlier this year I paid a mechanic to take apart all of my coolers (heatx, engine oil cooler, trans oil cooler, and aftercooler) and clean them out. It cost me a fair amount of money. And it was not needed -- everything was clean as a whistle

It's not oil smoke, so doubt turbo bearings. Anyway, the turbo was overhauled when I was accepting the boat -- to eliminate just this, and it made no difference.
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