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Man D2848 LE403 coolant level alarm.

Discussion in 'Engines' started by kev cribb, Sep 24, 2020.

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  1. kev cribb, Sep 24, 2020
    #1
    kev cribb

    kev cribb New Member

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    Hi all,
    Just wondering if any one has had this problem or could shed some light on my issue
    I ve got two MAN 800 hp D2848 LE403 engines. Went to start them the other day and the stbd coolant level alarm went off after a couple of seconds once the key was turned to position one as it should. The port alarm stayed on and refused to go off.
    Yes it’s completely full of coolant.
    I disconnected the stbd level sensor connector in the header tank under the filler cap and the alarm didn’t come on as it should.
    did the same on the port engine and the alarm still came on .?..
    are there two coolant level sensors on each engine ?
    Am I missing something somewhere.
    Any and all help would be really good. I am quite new here so please be gentle.
    Last edited: Sep 24, 2020
  2. Capt J, Sep 24, 2020
    #2
    Capt J

    Capt J Senior Member

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    Well Yes and no. There is a coolant pressure at expansion tank sensor. There is also a coolant pressure at water pump sensor. I'm not sure of your display but both sensors might light the same light.
  3. kev cribb, Sep 24, 2020
    #3
    kev cribb

    kev cribb New Member

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    Hi
    Thanks for helping. My engines don’t have expansion tanks. The manual says the light and diagram say it is coolant level alarm.
  4. Capt J, Sep 24, 2020
    #4
    Capt J

    Capt J Senior Member

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    They have to have expansion tanks.....the ones ON the engine......big metal tanks that hold coolant with a pressure cap
  5. kev cribb, Sep 24, 2020
    #5
    kev cribb

    kev cribb New Member

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    Hi ok yes with you now I’ve been reading lots and some have separate expansion tanks
    I don’t get why the stbd engine probe when disconnected doesn’t come on proving the the probe and system are working
    Yet the port one when the probe is disconnected still comes on. Could it be a problem in the connection cap metal connectors ?
  6. Capt J, Sep 24, 2020
    #6
    Capt J

    Capt J Senior Member

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    It sounds like you have some computer issues going on and you need to get a MAN mechanic to come out and hook up the laptop and verify what is going on. Could be alarm monitoring boards going bad or any number of items.
  7. mapism, Sep 25, 2020
    #7
    mapism

    mapism Senior Member

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    It's misleading to call them expansion tanks, because those are actually the shells of the heat exchangers, with the tubes bundle inside them.
    They just happen to be pressurized (on the coolant liquid side) when the engine is running, which is what makes their cap a critical component by the way.

    That aside, there can't be any computer issue on those engines, because they are the very last 100% mechanical engines that MAN built.
    Zero electronics anywhere, and nowhere to connect a computer. But they do have several sensors, of course.
    Off the top of my head, I would have said that there's only a level, not a pressure sensor - and only one per engine.
    But I can't be positive about that right now.
    And also about the sequence of how they normally work, though I believe the OP is right in saying that upon turning the key the warning light turns on for a second or two (just to confirm that the bulb inside is good) and then goes off without needing to actually turn the engine on.
    I can check all that directly on my boat, which happens to have exactly the same engines, but only in one week, when I'll be back onboard.

    Kev Cribb, if in the meantime you would like to check the 180 pages or so of the repair manual, I can send you the PDF file. Just PM me your mailbox address.
    Oh, and welcome to the asylum.
  8. kev cribb, Sep 25, 2020
    #8
    kev cribb

    kev cribb New Member

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    Hi thanks for your help. I ve read the 180 pages of the repair manual which is how I ended up getting membership of the asylum and meeting you on this ward. I think you and I are right that there is only one sensor for level and the wiring joins the wiring loom from all the other sensors. The parts manual does say there is an electronic unit in the system but where I have no idea. It’s just strange about unplugging the stbd sensor and the initial 2 second light not coming on. But when you do the same on the port it still comes on as an alarm ?? I’m going to open up the connector plug and clean the connector next week to see if that’s causing it. Failing that I am so stumped at what to look at after that. The relay perhaps??
  9. mapism, Sep 25, 2020
    #9
    mapism

    mapism Senior Member

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    The only electronic unit I'm aware of is the black box below, of which I've got one for each engine.
    But as you can see in the left side of the pic, where it's shown with its cover open, it's just a sort of concentrator for the engine sensors, to which the dashboard is connected.
    No real "intelligent" electronic inside it: you could throw it overboard, and the engines would continue to run.
    Which is something I rather like, though I appreciate that there are other advantages in electronically controlled modern engines.

    [​IMG]
  10. mapism, Sep 25, 2020
    #10
    mapism

    mapism Senior Member

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    Btw, I can't tell you by heart the exact size of the above box, but it's at least 1 foot high, give or take.
    Not something that you can really miss, if you look around your engine room.

    PS: another thought about my previous post where I tried to remember the warning lights sequence upon startup.
    I'm pretty sure that in my boats there are only two warning lights that stay on till the engine is actually started: oil pressure and alternator.
    Which makes sense, because unless the engine is running, there's neither oil pressure nor current charge from the alternator.
    So, the coolant light is bound to check just the level, for consistency.
    If there were also a pressure light, it should stay on till the engine is started.

    Note to self: remember to take a pic of all dashboard warning lights.
    It would be handy to add it to all other pics of technical bits... :)
    Last edited: Sep 25, 2020
  11. Beau, Sep 25, 2020
    #11
    Beau

    Beau Senior Member

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    Check for the electronic boxes to be mounted remotely on a bulkhead forward or to the rear of the engines.

    Also, I believe the alarm circuit may be completed by the probe end resting in the coollant?? if that's the case a closed circuit stops the bells, rather than an open circuit? Dunno, but maybe ....
  12. Fiammetta42, Sep 26, 2020
    #12
    Fiammetta42

    Fiammetta42 Member

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    What age and state are the batteries?
    One set may have started both engines , but then the port engine switched to its own / domestic when running .Its voltage when running despite its own alternator may not quite be enough to extinguish warning lights from sensors .How long did you run it with the low coolant light on ?
  13. kev cribb, Sep 26, 2020
    #13
    kev cribb

    kev cribb New Member

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    Both engines start first time from their own batteries. If it started and ran surely the light would go out ? all other alarms go out including oil pressure. I ran it for a couple of minutes and applied slight throttle in neutral which also didn’t help. are there any alarm / engine resets to try. I notice in the picture above the small black box has coolant sensor written on it. Is that a light or a reset on the side.
    I still can’t help wondering why the stbd one doesn’t work if the wires to it are not connected to the probe yet the port one does work even when not connected which leads me away from it being anything probe related.
  14. Capt J, Sep 26, 2020
    #14
    Capt J

    Capt J Senior Member

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    I have a 1100 hp MAN common rail boat that when the batteries are going bad or getting weak, it will light all kinds of erroneous engine alarms such as coolant pressure at expansion tank and 2-3 other alarms. So it could be voltage. Or the battery charger can be going bad and leaking AC voltage. Check for AC voltage with a multimeter.
  15. Beau, Sep 26, 2020
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    Beau

    Beau Senior Member

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    I still wonder whether it requires a closed circuit rather than an open circuit to quiet that alarm. Particularly because its the same alarm that's misfiring. With the wires off it certainly is an open circuit, and I am NOT suggesting you touch them together to test my theory! Test both probes in place with a continuity meter and a 12v current. If the quiet one shows a current and the noisy one doesn't it would seem to me that its closed circuit/off
    Last edited: Sep 26, 2020
  16. mapism, Sep 26, 2020
    #16
    mapism

    mapism Senior Member

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    As I recall, there are just warning lights and no buttons, but at the moment I can only go by the above photos.
    Happy to have a look in flesh, and also try anything else that might give you some indications, when I'll be back onboard.
    Unless you will have already found what's wrong by then of course, in which case I'd be very curious to hear about your findings!
  17. kev cribb, Sep 26, 2020
    #17
    kev cribb

    kev cribb New Member

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    Hi thanks for your help
    But I still am missing something here
    When they are both disconnected from the probes surely they would both do the same thing ie nothing ! but one continues to alarm whilst the one that works turns off. If they are not connected to the probes why test the probes. Why does the port one continue sounding when not connected and the stbd one doesn’t as I say surely they would both do the same thing either be off or continue sounding .
  18. kev cribb, Sep 26, 2020
    #18
    kev cribb

    kev cribb New Member

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    Hi
    If you don’t mind having a play when your next on your boat that would be really helpful. Of course should I find out the problem I will post here for everyone else. Thanks
  19. Beau, Sep 26, 2020
    #19
    Beau

    Beau Senior Member

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    Your right. If both are disconnected from the probes the probes are not the issue. I missed that factor. What you describe sounds like an open circuit shuts them off. So look for a short somewhere up the line that energizes the circuit on the one that will not shut off?? Where is the power coming into the circuit on the functioning alarm? A jump wire at the bells? Tied into the ignition behind the instruments?
  20. leeky, Sep 26, 2020
    #20
    leeky

    leeky Senior Member

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    +1 (You're a pretty good troubleshooter and a lawyer?:eek:)
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