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Cummins 270 Slow Cruise RPM-gctid343781

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    Cummins 270 Slow Cruise RPM-gctid343781

    I have twin Cummins 270 on a 3587 and found the most economical cruise is 1100 RPM @ 7 knts. Is this RPM to low to keep the oil flowing through the head. The engines run very smoothly but I am curious whether this may cause eventual damage if I maintain this speed over long term. I do run it up to high speed for 5 minutes at the end of each day after a long cruise to bring it up to temperature and blow out any carbon.


    The old school of thought was that you had to run diesels hard in order to get good longevity out of them.

    The current school of thought is that a properly broken in modern diesel engine can be run at moderate loading and you'll get much more engine life out of them than if you run them hard.

    I've even seen several instances where diesel engine life was measured in gallons of fuel burned, as opposed to the old mehod of hours run.

    Reading Tony Athens articles at his website...

    He has indicated that he has never seen a documented case of a cummins diesel having a shortened life by cruising at low power levels.

    To answer your original question...

    The amount of oil lubricating various engine parts is determined by the oil pressure in the system. If you have good oil pressure you're good to go.


    Whats the weather like on the boat

    Where am I right now?


      I have a 4087 with twin 250's, I run about 1200rpm, get 4.8gph combined.

      I take them up once a day to WOT to clean the injectors out. Running slow rpm's won't hurt engine life, but can clog injectors if you don't run them up, I was told by my mechanic.

      Even running up to 2500rpm (WOT for me), for 15 min each day, doesn't hurt my GPH number.

      One issue I have, if I don't get over 1100rpm, my batteries won't charge, according to the gauge anyway.

      1996 4087 Lazy Days
      2011 11’ West Marine Rib 350 Lazy Mac
      2011 Porsche Cayman
      2010 Lexus IS 250C
      2008 Honda Ridgeline


        I agree with the posts above. Oil pressure is king. That being said a certain load is probably healthy, and I would experiment with one engine too. How does the boat feel with one engine running a bit harder to do 7 knots? Auto pilot happy? Noise levels and vibration lower? I expect the single engine load might be a bit better fit for that big engine and single engine economy seems pretty widely reported here as being better.

        Cheers steve