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MTU 4000 thermostats fail position

Discussion in 'Engines' started by C4ENG, Dec 1, 2018.

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  1. Capt J, Dec 3, 2018
    #21
    Capt J

    Capt J Senior Member

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    I'm not sure as I wasn't there when the tech pulled all of that stuff apart. I think it uses seawater, with a thermostat, but might be coolant. On the seatrial the cat tech mentioned which thermostats were bad...…as well as the leaking turbo at the hot housing joint......injector pump leaking.....and on and on......also had the injector pump replaced, turbo rebuilt, starter replaced because a raw water hard pipe joint leaked on top of it in under 50 hours. Entire wiring harness replaced by 100 hours, computer replaced......numerous issues...… I also know of another one that grenaded with low hours. And I ran another boat and that one had thermostat issues on one engine with 10 hours on it......they run at 135-138f at cruise when a thermostat is bad.
  2. PacBlue, Dec 4, 2018
    #22
    PacBlue

    PacBlue Senior Member

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    The S4000 uses a split-circuit cooling system, here is a visual aid:

    upload_2018-12-4_9-5-13.png
  3. Capt Ralph, Dec 4, 2018
    #23
    Capt Ralph

    Capt Ralph Senior Member

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    Interesting.
    Yep, the oil temp is thermostatically controlled.
    Both engines failing at the same time is still funny. I wonder if a coolant change or some other service was preformed to help the thermostats fail at the same time.
    I (we all) have learned something new. Probably good re-reinforcement why I call FDDA for MTU work.

    The attached diagram does remind me, MTU has better booze & drugs.
  4. Beau, Dec 4, 2018
    #24
    Beau

    Beau Senior Member

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    Well, I am a glad that the OP's friend solved their problem. I just don't understand the fix. My ole' 820's are just purring along and that's fine with me.
  5. C4ENG, Dec 4, 2018
    #25
    C4ENG

    C4ENG Senior Member

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    From what I was told (but did not see for myself) was that MTU 4000 have 4 thermostats.
    There where no other issues other than the engine lube oil temp.
    My friend did not get a lot of information on exactly how that was the failure. He asked the tech if they could test the thermostats but they told him no. He did not feel like pushing any issues with them now the job is done and they are gone, he is on to other battles like the VFD for the bow thruster that quit working and the fuel separator that wont go out of alarm mode and a captain who wants to leave yesterday... Oh the joys of engineering on yachts.
  6. Capt Ralph, Dec 4, 2018
    #26
    Capt Ralph

    Capt Ralph Senior Member

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    Per the diagram in post #22, I would think the charge air temp and dentistry would cause errors.
  7. Beau, Dec 5, 2018
    #27
    Beau

    Beau Senior Member

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