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Onan 27kw random shutdown

Discussion in 'Generators' started by TahoeJohn, Aug 24, 2021.

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  1. TahoeJohn, Aug 24, 2021
    #1
    TahoeJohn

    TahoeJohn Member

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    One of our Onan 27kw (MDKAF) generators has started to randomly shut itself down. Sometimes it will run for 2 hours before doing so while other times it happens after a few minutes. Load doesn't seem to be an issue. Nothing has been done to it recently; its last annual service was in November.

    I did do a static fuel pressure test which was fine: 5.5 psi, within the range of 3.5 and 6psi.

    The other things mentioned in the manual that could shut it down:
    S2: High engine temperature
    S3: Low coolant level
    S4: Low oil pressure
    S5: High exhaust temperature

    While I don't think any of these conditions are occurring, it could of course be a faulty sensor. However, these conditions (when encountered), should trip the "fault condition CB2" breaker (picture below), but that breaker has always remained closed, even when the unit shuts itself down.

    Is my understanding of how this breaker works correct? Do the 4 conditions above trip this breaker when encountered?

    gen controls.jpg
  2. DOCKMASTER, Aug 25, 2021
    #2
    DOCKMASTER

    DOCKMASTER Senior Member

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    I do not believe the shut down sensors you list trip that breaker. If you have two of the same gen, start swapping sensors to see which one shuts down the other gen.
  3. Capt J, Aug 25, 2021
    #3
    Capt J

    Capt J Senior Member

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    Could also be a dirty heat exchanger and it's getting up to the shut down temperature.
  4. TahoeJohn, Aug 26, 2021
    #4
    TahoeJohn

    TahoeJohn Member

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    Two good suggestions, thank you! I do have two of the same generators so I'll first check the HE and then start swapping sensors, one at a time.
  5. Capt Ralph, Aug 28, 2021
    #5
    Capt Ralph

    Capt Ralph Senior Member

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    Pascal was here before on his previous work boat when he took it over.
    Fresh sensors all around I recall took care of it.

    I remember going around in circles on new install sets, including my own.
    Bad senders will require lots of aspirin also.

    When fixed, you will remember your Excedrin Headache # 27 well.
  6. LM Viking, Aug 28, 2021
    #6
    LM Viking

    LM Viking Member

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    Could it be intermittent loss of current to or failure of fuel solenoid . Had my 9kw Onan shut down with low voltage when trying to start mains with bad batteries. Like a faulty connection?
  7. TahoeJohn, Aug 28, 2021
    #7
    TahoeJohn

    TahoeJohn Member

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    Thanks, CR. Something to consider. Sensors are not expensive and most (except for the exhaust temp) are fairly accessible. Maybe just start with oil pressure, coolant temp, and coolant level sensors and see if it goes away.

    Thanks, LM. I did look for loose connections but didn't find anything in my initial search. Also, the 12V system for the generators is completely independent from the 24V mains starters. But it's something to keep an eye on, for sure.