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Onan 8.5 Kw

Discussion in 'Post Yacht' started by Stainless45, Aug 13, 2021.

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  1. Stainless45

    Stainless45 Active Member

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    Post 46 Long Island NY
    The boat came with a 1990 vintage Onan 8.5kw generator of unknown hours. It runs great and makes solid electricity but lately it's been using oil and coolant. I do not have the budget for a new one so my question is has anybody overhauled one of these little 3 cylinder units? Are parts kits available?
  2. Tight Lines

    Tight Lines Member

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    To piggyback on @Stainless45’s question, how much life can be squeezed out of the Onan if property maintained?
  3. Prospective

    Prospective Senior Member

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    I'm not sure anyone can really answer that. I have a 9kw Onan that's original to my 2000 43' Ocean. It's got some rust but uses no oil or coolant and starts/runs without issue every time with about 3500 hours. Now, with my luck, after this post I'll go to start it up next trip and it will burst into flames. But so far so good.
  4. Pascal

    Pascal Senior Member

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    I had a pair of Onan 27.5 on a boat I ran with 7500 hours. Running good. I ve had Northern lights with 8000 running good as well

    most diesel gens should make it to 10k or more
  5. Tight Lines

    Tight Lines Member

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    Is there a kit (OEM or aftermarket) to add gages or idiot lights to the gennie? I would love to have basic vitals on the Onan to spot a problem before anything serious happens.
    Stainless45 likes this.
  6. DOCKMASTER

    DOCKMASTER Senior Member

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    My original Onan 20kw had 7700 hrs on it when I pulled it and it still ran Ok but wouldn't hold Hz very good. My 8kw Kohler blew a head gasket or cracked a head at just under 4k hours. I talked to the owner of Northern Lights when after I bought my new gens from him and asked what was realistic for hour expectency. He said 10k hours minimum with normal maintenance and it is not uncommon to have units go over 20k hours. And they have some that have gone much more. I had already bought the gens and told him I just wanted to know so he had no motivation to embelish.
    TahoeJohn likes this.
  7. Greg Page

    Greg Page Active Member

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    We just replace the Onan with a new 9Kw Kohler. IMG_3492.JPEG
    Stainless45 and chesapeake46 like this.
  8. Rich M.

    Rich M. Member

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    Check your antifreeze cap check the overflow hose to the reservoir and what weight oil are you are you using
    cleanslate likes this.
  9. Stainless45

    Stainless45 Active Member

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    Post 46 Long Island NY
    Been using straight 40 weight
  10. Stainless45

    Stainless45 Active Member

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    Update- Oil use isn't as bad as I had thought, still watching the coolant as it seems to use some. My mechanic thinks it's running hot and we put some barnacle buster through the unit. Sometimes it runs great, other times there is a fault that causes shut down. Still troubleshooting. And it's an 8kw not 8.5
  11. Davidoc

    Davidoc Senior Member

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    Take a laser reading at the thermostat housing near the sensor at the time of the fault. Verify that it's going over 180゚. If you've tried all the normal stuff impeller etc check the strainer O ring for for an air leak and if that doesn't do it your raw water pump may be worn out. Mine got to the point where it could not draw water from the strainer Without some type of assistance. I actually had to fashion an external pump to pump water through the generator in order to save an extended trip in the Bahamas. You can get a flush cap for your strainer fyou're strainer from seaboard marine marine in order to allow water to come in from another source or to assist in flushing your engine
    Stainless45 likes this.
  12. Capt J

    Capt J Senior Member

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    You missed the part about it losing 1/2 a gallon of coolant per day. Coolant gets low, coolant temp rises, it hits the temperature shut down.
  13. Davidoc

    Davidoc Senior Member

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    I didn't see that from stainless.
  14. Pascal

    Pascal Senior Member

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    I always have a spare pump on board. Always. And impeller of course.
    Davidoc likes this.
  15. cleanslate

    cleanslate Senior Member

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    Perhaps a heat exchanger or exchangers/coolers, not sure if you would have one or more, causing your oil and coolant loss issues....just a thought. I think sea water intrusion would be in the mix also. But you never know. Your fluids could be going right out the exhaust.
  16. Stainless45

    Stainless45 Active Member

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    Yeah I'm going to take it to be pressure tested next week. I think you are right
    cleanslate likes this.
  17. SplashFl

    SplashFl Active Member

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    It's a Kubota engine so parts should be available outside of the crooks at Onan. Before boat was sold I used to get parts at a local Phasor distributer for a LOT less. Buddy sailing around the world reported his 8kw was starting to get tired at 50,000. hours before selling the boat. He had rewired the control box getting rid of the solid state circuit board.
    Stainless45 likes this.
  18. Forrest Gump

    Forrest Gump New Member

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    I have a running take out Onan 8KW if your intersted. 3,675 hours, full log book of maintenance and repairs. located in CT
  19. Stainless45

    Stainless45 Active Member

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    I will let you know if this one happens to fail. For now the budget demands that I try and keep her going as long as possible.
  20. SplashFl

    SplashFl Active Member

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    I remembered once getting this revised wiring diagram when buddy eliminated the circuit board in his 8kw. She had been a hurricane Andrew total.

    Attached Files: