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Onan Continuous duty oil change interval

Discussion in 'Generators' started by gcsi, Jan 8, 2022.

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  1. gcsi

    gcsi Member

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    I have a pair of Onan 21.5MDKAE gen sets. This spring, we’ll be spending considerable time on the hook in a tropical climate. The manual recommends 200hr oil change intervals. If the unit is operating continuously, can the oil change interval be extended? My reasoning is two fold; 1) units will have less “wear” as a function on not having cold starts, 2) units will be operated at 50%+ load capacity with little chance of cylinder glazing.

    Any thoughts or input would be most appreciated.
    Brett
  2. gr8trn

    gr8trn Senior Member

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    Interesting, your reasoning sounds reasonable. I generally give the manufacturers the benefit of the doubt on service intervals, in that, they are aware of load and cold start "wear" as well. This interval is, also, probable somewhat traditional and conservative so I get the curiosity especially with continuous operation as you are about to see.

    Other than being annoying and more to do more often and more boat dollars spent I vote 200 hours.

    In my experience good fresh oil matters. I don't know what happens if you stretch the interval as I don't. But I do know that regular timely oil and filters changes have created a lot of longevity in my Yanmars and Cummins. My cars over 100K love it too.
  3. Pascal

    Pascal Senior Member

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    I would stick to Onan’s recommendation. Doing an oil change on a gen is a 15 minute job.

    I Just did both of our 45kw Onans which uses cummins 4BTAs with 250hrs interval. So we get 20 days between oil changes as I rotate them one or two days. 2 x 15 minutes every 20 days is no big deal... or every 2 weeks in your case

    I don’t think cold starts or load as much of an impact on oil. Diesel engine oil gets dirty from combustion... I would probably argue that heavier loads probably make it worse
  4. Ken Bracewell

    Ken Bracewell Senior Member

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    I've always changed oil at manufacturer recommendations, and religiously send oil samples out for lab analysis. And I always run generators for extended periods of time. I think you should still with 200 hrs.
  5. olderboater

    olderboater Senior Member

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    I follow all manufacturer service schedules and that includes oil changes for generators and send samples out each time as well. If at 190 hours and 200 is going to be inconvenient, then I do it now. Sometimes sooner, never later. We do not anchor as much as some here like Ken and Pascal, but if we did, we'd still stick to the numbers. We do run gens anytime we're not connected at a marina.
  6. Capt J

    Capt J Senior Member

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    I'd stick with 200 hours. Really it's 8 quarts of oil and a filter and like everyone else, I can knock out just an oil change in 30 minutes. I wouldn't try to go longer.
  7. olderboater

    olderboater Senior Member

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    When it comes to maintenance, I'm a strong believer in discipline. Cheating a bit always starts somewhere. I can easily justify stretching 200 to 250 hours, but by doing so I can stretch 500 to 700 and 1000 to 1500 and 4000 to 8000 and then I'm angry when the boatyard tells me the costs of a rebuild of my large engine and I scream how Cummins, Volvo, CAT, MAN, or MTU is garbage and I'll never have another.
  8. Slimshady

    Slimshady Senior Member

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    Fewer cold starts will definitely increase engine life but does nothing for oil change intervals. Like everyone said, stick with manufacturers rec. You'll get good at quick oil changes! Keeping engine running at proper temp and load is very important to long life
  9. Capt Ralph

    Capt Ralph Senior Member

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    Another thought;
    I have been pushing Shell T5 synthetic blend in the gen-sets we service. This includes our own sets.
    250 and 350 hour lab lab reports have a long history of clean and super clean.
    I did not start this by pushing any mfg service interval, but to offer a little protection in those OOPPSS moments.

    If you worry about your gen-sets, purchase the SOS kits and send them in regularly.
  10. Lepke

    Lepke Member

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    I use a centrifuge and batch clean about 50 hours. I take a sample (before centrifuging) from running engines a couple times a year. After cutting open filters over several years, I now only change the filters once a year. I get excellent oil test results and haven't actually changed oil since 2011. Just make up oil.
  11. Capt Ralph

    Capt Ralph Senior Member

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    Do you centrifuge the oil on a by-pass system or when the engine is not running?
    If I'm already off the course, could you explain for us swamp folk?