What can cause diesel to be overloaded intermittently?

Discussion in 'Diesel Engines' started by Northeaster, Sep 15, 2018.

  1. BlueBell
    Joined: May 2017
    Posts: 807
    Likes: 88, Points: 28
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    You've changed so many things it could be anything!
    Or, worse yet, a combination of things.
    I think you need some on-sight help.
    Someone who knows what's going on and is a good troubleshooter.
    I don't envy you.
    Good luck with the painting.
     
  2. Northeaster
    Joined: Sep 2011
    Posts: 261
    Likes: 8, Points: 18, Legacy Rep: 45
    Location: Eastern Canada

    Northeaster Senior Member

    Bluebell - did you watch the video on the last page? What is it that strikes you as alarming or requiring such concern? I appreciate the replies but I do think that we're blowing this a bit out of proportion. We know that my diesel is overloaded by having too much weight So for the next few outings, I will not push the throttle too much. As I am almost done adding weight to the boat it is now really a matter of working with my propeller guy to remove possibly one or two inches of pitch or whatever is required to be able to achieve maximum RPMs under load, once the end weight is known.
    The purpose for me starting this post was to see if I had missed possible causes of intermittent overloading. But, as my fuel system was new with little use, air filter good, prop and bottom clean etc I think that it seems a matter of being overpropped enough that any added weight or adverse wind and seas reduce my rpms and therefore available hp, thus causing lower achievable speed. If I reduce pitch to the point where I can hit 2800rpms,with people on board and towing a dinghy, I think my overloading issues will be gone. Stupid of me to add pitch last time but we make mistakes sometimes.
     
  3. BlueBell
    Joined: May 2017
    Posts: 807
    Likes: 88, Points: 28
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Yes, I watched the video.

    What makes you think I am alarmed or overly concerned?

    So, it runs fine for half an hour and then overloads.
    Weird.
    Strange, odd, even ridiculous, but if your not concerned, then don't worry about it.

    I guess to respond more correctly to your post: I have no idea why.
    Maybe just focus on your painting.
     
  4. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    Update - I had 2" of pitch taken off the prop during the winter. Had the boat out briefly when I put it in a couple of weeks ago (haven't been able to get out since).
    With the pitch taken off the prop, I am now able to get 3000rpm WOT (max intermittent rpm for the engine is 2800rpms which delivers 150hp).
    This was by myself, but with new aluminum floors in (replacing somewhat waterlogged temporary OSB / ply floors), but most gear aboard like anchors, full tanks, etc.

    So, I think i am good for now- engine should not be overloaded this year... Even with a couple families on board and beach gear, I should still hopefully be able to hit perhaps 2500rpm or so (which is max continuous rpms).
    I may end up building a small cabin some day...but that could be a year or two, or never... if i add more weight then, i may have to de-pitch again but at least for now I wont kill the diesel prematurely..
    thanks all for the input!
     
  5. Lepke
    Joined: Sep 2015
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    Location: Oregon to Alaska

    Lepke Junior Member

    An overtaking following sea is trying to turn your props backwards. Depending on your draft, wave height, and overtaking speed of wave will load and unload the engines.
     
  6. Northeaster
    Joined: Sep 2011
    Posts: 261
    Likes: 8, Points: 18, Legacy Rep: 45
    Location: Eastern Canada

    Northeaster Senior Member

    Thanks for the info Lepke- i had not heard that before - and with the engine already at the point of overloaded, due to overpropping, I would guess that might be more dramatic than if the engines had plenty of reserve torque and hp... now that it is not overpropped, I will see if the intermittent rpm drops subsides ..
     
  7. Magnus W
    Joined: Nov 2017
    Posts: 135
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    Location: Sweden

    Magnus W Senior Member

    Your maximum rpm is 2800 so I assume it shouldn’t rev much past that unloaded as the governor would prevent it, perhaps 3000 rpm?

    You said earlier that you could reach 3300 rpm. Are you certain that the tach is accurate?
     

  8. Northeaster
    Joined: Sep 2011
    Posts: 261
    Likes: 8, Points: 18, Legacy Rep: 45
    Location: Eastern Canada

    Northeaster Senior Member

    I am not certain the tach is accurate, but its it works off the teeth on the flywheel, and my understanding is this type is not often off like the ones which work from an alternator, etc. It idles at 800 rpm on the tach so it is not way off, if st all. I could be wrong but did not think the governor would restrict it from revving high in neutral/ no load..

    New Update - i did have the prop depitched by about 2 inches which helped, but the larger issue i found was the air filter restricting flow and causing excess fuel under load.
    What buys me is that last year, when it would not rev up enough, and had excess fuel in exhaust, I removed the air filter briefly to see if it made a difference, and it did not appear to. This year, the prop work helped me rev higher, but when i still could not rev up fully and experienced excess fuel smoke in the exhaust, I once again tried removing the air filter and saw an instant rpm gain of say 400rpms. zput it back on and rpms went way down. There was soot / blow by in the filter so I cleaned and dried it and it was better but still restrictive under higher loads. I have since replaced with a larger filter and added a 90 degree elbow to keep the filter higher and possibly reduce soot from blow by and so far so good.
    I can hit 20 kts at 2800rpms, with WOT in neutral hitting approx 3200-3300 rpms, so perhaps the tach is off a bit. I will see our (very busy) local diesel mechanic at a Marina party in a couple of weeks so I will ask him about checking my rpm accuracy when he has time.
     
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