Underloading a Diesel

Discussion in 'Diesel Engines' started by Paul F, Oct 3, 2011.

  1. michael pierzga
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    michael pierzga Senior Member



    I dont know much about turbos and their behavior. In general because of a water cooled exhaust manifold A marine engine runs cold. An Auto engine runs Hot. Ive just been running for 28 hrs and I can comfortably rest my hand on any part of the engine block.

    On a lightly loaded marine engine its clogging of the exhaust system that I notice first. This condition may also effect the turbo. Best to ask a Marine diesel engineer for advice if you will be running your powerplant for long periods underloaded. I would think that he would recoment a shorter maintanence cycle.
     
  2. FAST FRED
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    FAST FRED Senior Member

    "Ive just been running for 28 hrs and I can comfortably rest my hand on any part of the engine block."


    Every engine , marine or not, has a "proper" operating temperature .

    Usually 180F to assure efficiency.

    Long term operation at cold temperatures will assure excess fuel use, and shorten engine life.

    Cooling the turbo heated air does increase power as the air is more dense.

    But the engines inlet temperature is never the engines operating temp.

    Evans coolant is now being used in larger trucks to be able to increase the operating temperature , usually 235F thermostat.
     
  3. whitepointer23

    whitepointer23 Previous Member

    our new kenworth runs at 90 to 110 celsius, i believe this is to get maximum fuel burn to meet emissions rules and the fuel economy is excellent as well. 1.79 km to the liter .
     
  4. Paul F
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    Paul F Junior Member

    Thankyou all, as I have said before I am new to understanding the operation of a diesel engine. My conclusion is that to vary the RPM as much as possible, and combine low RPM / power use with peroids of higher load. I have always believed in very short oil change cycles, oil is cheap when compared to an engine re-build.

    I do have another question, re the govenor in the injection pump, I will start another thread.

    Regards, Paul
     
  5. Frosty

    Frosty Previous Member

    Just driven from Bangkok to Malaysia yesterday in my Mazda deisel 2.5 12 valve. I cruised at 135KMH and I swear I did not press the gass pedal more than .1/2inch (I looked) 14 hours drive --is that light load . I do this on a regular basis and it has now 249.000km no smoke no oil burned AT ALL.

    You could noty run a boat lighter than that.
     
  6. powerabout
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    powerabout Senior Member

    just what it was designed to do
    now go uphill at max rpm / load for 249,000 k's and see how it lasts
     
  7. Frosty

    Frosty Previous Member

    Your missing the point. The thread is questioning running a diesel on light loads and how it damages them --how light do you want.
     
  8. powerabout
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    powerabout Senior Member

    Well yes and no Frosty
    ( yes that was light load)
    I saying an engine that is designed to run full power all the time could/might/are more of a problem at low load than a diesel that is designed for a lighter load such as passenger road transport.
    Usually in the modern turbo world less compression ratio and more ring/piston clearance so they suffer more at no load and long term with the oil dilution that comes with that problem. Its a ring - bore sealing issue
    Cant see it happening to an old Gardner and engines of that ilk though
     
  9. michael pierzga
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    michael pierzga Senior Member

    I dont know the engineering, design, brief for an automobile engines lifetime loading. Obviously you cant run your auto at 65 to 75 percent output all the time or you will generate a massive wedge of traffic tickets, have literally one billion smashed insects on your windshield , chew thru mountains of tires and most importantly never be able to stop long enough to enjoy a cold beer.
     
  10. Frosty

    Frosty Previous Member

    Lets not get too far away from topic, the guy is asking about a 2.8 Isuzu.

    I think my example proves that no damage occurs.

    The writer was not asking about a gardener.
     
  11. Easy Rider
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    Easy Rider Senior Member

    Frosty,

    How far you "press the gas pedal" dos'nt determine how loaded your engine is. The percentage of max fuel burn does. If your engine burns 10gph at WOT at the rated power engine speed and you are burning 3gph you're at a 30% load. You can have high engine speed and light load or low engine speed and heavy load. The amount of heat generated is about proportional to the amount of power delivered. A diesel engine can rev quite freely without much "throttle" partly because there is no throttle. It can freely ingest all the air it wants all the time. The boat however has a different engine brake/load than the car and you can't lightly load the engine at high engine speed. So with a boat the "throttle" may be deployed 50% but that dos'nt mean the engine is at 50% load. And if you are at 50% engine speed and propped right that dos'nt mean you're at 50% load either. But if your'e burning 50% of the fuel you can burn you actually are at 50% load.
     
  12. cor
    Joined: May 2008
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    cor Senior Member

    Frosty, that is a light load.

    I think that what powerabout is saying is that a marine engine is designed for heavy load, auto engine is designed for light load. The difference in the engine design may be the piston to bore clearance and the ring tension and type.

    Maybe the auto engine has square cut rings with high tension to keep the cylinders clean? The trade off being that this setup would wear faster with high load (higher cylinder pressure).
     
  13. Frosty

    Frosty Previous Member

    Your all missing the point , got off topic and are missing the original question above.

    The guy has a small Izuzu (like me and my car) and he wants to know what damage if any would accour under light load, the answer is none (like mine)

    Who mentioned marine engines, where did that come in?
     
  14. michael pierzga
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    michael pierzga Senior Member

    Well, this morning I stopped by the engine shop to drop off injectors for service. I asked the engineer what are the consequences of running an engine unloaded ? He walked me over to a generator. This generator had only 4000 hours and was running smokey. He showed me the pistons and cylinder walls. Glazed, polished smooth like a mirror and no longer round but elliptical.
     

  15. Frosty

    Frosty Previous Member

    Thats how they are supposed to be. What do you expect after 4000 hours

    Elliptical? he even gave you a digital vernier to measure it with or you could see it by eye.

    The piston does nothing but hold the rings and its something to connect the con rod to. A smooth piston is inconsiqential.
     
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