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Kohler 7.5 R Generator Shutting Down

Discussion in 'Carver Yacht' started by Thisisit, Jul 13, 2015.

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  1. Thisisit, Jul 13, 2015
    #1
    Thisisit

    Thisisit Member

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    My Kohler 7.5R has worked flawlessly for over 20 years. This past weekend, it began the habit of simply shutting down after 25 seconds of running. The symptoms are as follows: Starts fine and runs; output voltage is normal; stops after 25 seconds; doesn't sound like it is starving for fuel. It shuts down as if I was turning it off. It will start immediately after shutting down and will run another 25 seconds or so. I have tried the following:
    Load on
    Load off
    Disconnected water temperature sender
    Disconnected oil pressure sender
    Switched fuel supply
    Cooling water (raw water cooled) has normal flow

    The oil pressure gauge reads a normal (and suggested) 20 psi. I'm wondering if the unit is getting a false over- load signal. My voltage gauges do not move from, their no-load 125 volts.

    Any ideas, fellas?
  2. Capt Ralph, Jul 13, 2015
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    The old 4 bang Kohler 7.5r has a fault delay of 20 to 30 seconds. Sounds like you have a fault and it's shutting down. Low oil pressure, high water temp or no 12volt exciter voltage. unplug the wires from the senders. make sure they did not get hot and short to the block. If your making good electric in those 25 secs the gen end should be good.
    That lil logic board is still available and probably the fault if all else is good.

    On another note. Kohler had a factory recall on the exhaust riser. If yours is still cast iron, look up their web site and get the new stainless one installed, no charge. This could save a life,, yours??

    ,rc
  3. Thisisit, Jul 13, 2015
    #3
    Thisisit

    Thisisit Member

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    Yup, I had disconnected the temp sender and the oil pressure sender. Same problem. Didn't think about the 12 volt exciter voltage. I will have to read up on the diagnostic test for that. I will also look up the cost and availability of the logic board and if that's the issue, well, it is what it is.

    We had our exhaust riser replaced many years ago but good job bringing it up again. Every unit needs to be retrofitted.

    Thanks for replying.
  4. Thisisit, Jul 17, 2015
    #4
    Thisisit

    Thisisit Member

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  5. Thisisit, Jul 17, 2015
    #5
    Thisisit

    Thisisit Member

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    My model has a distributor. I believe the 12VDC exciter current is for magneto ignition only.
  6. Capt Ralph, Jul 18, 2015
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    The mag (distributor) makes it's own voltage. Don't look in there for a problem, If it runs, no problem in there till you induce one. That loose wire is the kill wire like a lawn mower or outboard. It goes back to that relay board.
    The exciter 12 volts I mentioned you have or you would not be making 120Vac as stated in your first post; output voltage is normal. I assumed you meant the 120Vac was o k.
    Are you really making 120Vac?
    If so, either you have an engine failure (oil, temp), a bad sender (oil,temp), a bad wire from the oil or temp senders shorting to the engine/frame or a bad relay board.

    Something else to remember, your in a gasoline environment. Keep the area ventilated and no sparks.
  7. Capt Ralph, Jul 18, 2015
    #7
    Capt Ralph

    Capt Ralph Senior Member

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    You may have an electric choke, unplug that wire and try again. A load there could (I guess) induce a problem.
  8. Maybe Knot, Jul 18, 2015
    #8
    Maybe Knot

    Maybe Knot Member

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    Check the oil level.
  9. Thisisit, Jul 18, 2015
    #9
    Thisisit

    Thisisit Member

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    rcrapps: I did isolate the choke. Same result.

    Maybe Knot: oil level was checked early on. it's up and the pressure is at recommended level.
  10. Capt J, Jul 18, 2015
    #10
    Capt J

    Capt J Senior Member

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    Does it have a sender on the exhaust manifold *(temp?). Does it have an auto shutdown for a fire system? I would check for a burnt or bad wire. But if you're just going to throw parts at it, get someone in who can properly diagnose and fix it.
  11. Capt Ralph, Jul 18, 2015
    #11
    Capt Ralph

    Capt Ralph Senior Member

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    If your really making 120Vac for the 20 seconds it's running; Then call a kohler shop and have them double check your findings & put in a relay board.
    I'm a little paranoid working in a gas environment. More nervous with a owner going under the covers of anything. So far you have been looking on the outside.
    You would have some warranties on the board also if a real Kohler guy puts it in.

    Good luck,
    rc
  12. Thisisit, Jul 18, 2015
    #12
    Thisisit

    Thisisit Member

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    I like to do the basic diagnosis and eliminate the obvious stuff. I'm almost at the end of the DIY list. I don't simply "throw parts at it" until I have done my due diligence.

    I have contacted my Kohler specialist and he seems to think I've narrowed it down to only a couple of things, one being the board. We'll see....
  13. Capt Fred, Jul 19, 2015
    #13
    Capt Fred

    Capt Fred Senior Member

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    As Capt J mentioned, have you isolate the exhaust temp sensor? Not sure you have one but if you do then it needs to be isolate/tested.
  14. Thisisit, Jul 19, 2015
    #14
    Thisisit

    Thisisit Member

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    I will have a look at it right now and see if I have one. I have a feeling though that even if it was a temp sensor going to ground, my experience has been that it takes a few minutes for it to cool off in order for the circuit to open again. My unit will fire back up again immediately after stoppage and run for 20 seconds again. Nevertheless, I will certainly test this sensor as well.
    Thanks for the tip, Capt Fred
  15. Capt Ralph, Jul 19, 2015
    #15
    Capt Ralph

    Capt Ralph Senior Member

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    Per the book. There may be a bad fuse.
    7.5r.jpg
  16. Capt Ralph, Jul 19, 2015
    #16
    Capt Ralph

    Capt Ralph Senior Member

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    Pretty sure there is not a temp sender on the riser.
    Just oil and block (water) temp.
    7.5r 1.jpg
  17. Thisisit, Jul 19, 2015
    #17
    Thisisit

    Thisisit Member

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    No temp sender on the exhaust riser. Had a look at the schematic (thanks rcrapps). Diving down to look for that fuse.
  18. Capt Ralph, Jul 19, 2015
    #18
    Capt Ralph

    Capt Ralph Senior Member

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    The book shows data for two different spec'd 7.5Rs.
    One set has a monster of a mother board and three fuses on the back, the other 7.5R data refers to a set with a small board with a 3 pack of relays (I had one of these) and two fuses on the box.
    As far as a gas set goes, I loved that old flat top.
  19. Thisisit, Jul 19, 2015
    #19
    Thisisit

    Thisisit Member

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    You're right, there's 2 fuses on mine. A 10 amp and a 2 amp. Guess what! Go ahead, guess! 2 amp fuse is toast. Now, just looking thru my stock for another 2 amp. Then a quick test and try to figure out why it blew. Must be a reason although it doesn't look burned. it's one of the rough service types that may have just given up with all the vibration.
  20. Thisisit, Jul 19, 2015
    #20
    Thisisit

    Thisisit Member

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    Thanks to all for the help. Great bunch of boaters, the whole lot of ya. Thanks to rcrapps for the jpgs. and the help.
    Margaritas on me the next time I'm in JAX!