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Running MTU's at low RPM?

Discussion in 'Engines' started by MLILIENTHAL, Dec 18, 2020.

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  1. MLILIENTHAL, Dec 18, 2020
    #1
    MLILIENTHAL

    MLILIENTHAL New Member

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    I'd appreciate some insight from those who've run or been around MTU's for a while. I've had CAT and Cummins engines for 20+ years and now looking at a boat with MTU 16v2000's. Other boats I'm looking at have MTU's or Mann's so this question isn't necessarily specific to that engine model. Its a European boat and made to run on plane at 25 - 30 kts. Of course with that speed in a large boat comes a hefty fuel burn. My question is how do these engines do running at lower rpm for long periods? I plan on some longer trips and would run it slower so to reduce fuel burn and extend the range. Neither my CATs or Cummins had an issue with that but MTU's are new to me.

    Thanks

    Matt
  2. olderboater, Dec 18, 2020
    #2
    olderboater

    olderboater Senior Member

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    All engines designed to be run at planing speeds have the same basic recommendations and generally that is to open them up every few hours to 70-80% load for a brief time but otherwise fine to run at low load. However, many will argue that even that isn't needed. Nothing unique about MTU in any of this. The issue is engines designed to be run at planing speeds.
  3. MLILIENTHAL, Dec 18, 2020
    #3
    MLILIENTHAL

    MLILIENTHAL New Member

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    Thanks for your reply. Being a bit more of a high performance engine (hi hp/wt ratio) I thought maybe they might have more of a propensity for loading up. I ran my Cats at idle to 1200 rpms for several days when running the intercoastal with only one or two opportunities to open it up and had no issues so hoping these would operate similarly.
  4. Soulstice, Dec 18, 2020
    #4
    Soulstice

    Soulstice Member

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    Also remember that many of these engines were put into sportfish style boats which are designed to run at plane for long distances and then run at low rpm when trolling for many hours. I don’t think it is a problem with these engines as long as you spool the engines up and run then at planing speeds towards the end of a trip when you’ve been running at low rpm’s for extended amounts of time. This will help the turbo heat up, burn off any carbon that’s been building up and generally clean out your engines before you end a trip.
  5. NYCAP123, Dec 18, 2020
    #5
    NYCAP123

    NYCAP123 Senior Member

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    Basic rule of half-hour out of 8 stands for all motors I'm familiar with.
  6. MLILIENTHAL, Dec 19, 2020
    #6
    MLILIENTHAL

    MLILIENTHAL New Member

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    Thanks for your insights gentlemen.
  7. Pascal, Dec 19, 2020
    #7
    Pascal

    Pascal Senior Member

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    As long as they are running at normal operating temp they ll be fine. In most cases hull speed will keep them at normal temp
  8. MLILIENTHAL, Dec 19, 2020
    #8
    MLILIENTHAL

    MLILIENTHAL New Member

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    Don’t they usually put trolling gears in sportfishers so you do troll for long periods at low rpm?
  9. Pascal, Dec 19, 2020
    #9
    Pascal

    Pascal Senior Member

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    Yes but that’s so they can troll at very low speed. And then, being sportfishes, they run flat out back home. :)
  10. Beau, Dec 19, 2020
    #10
    Beau

    Beau Senior Member

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    Trolling valves control the amount of oil/ pressure in the tranny. They let the pressure plate "slip" to gain lower troll speeds because of reduced prop rotation. They do not reduce RPM of the engines.
  11. MLILIENTHAL, Dec 20, 2020
    #11
    MLILIENTHAL

    MLILIENTHAL New Member

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  12. Soulstice, Dec 21, 2020
    #12
    Soulstice

    Soulstice Member

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    Exactly what Beau said about trolling valves. For what it’s worth, I have never had trolling valves on any of my engines. On a normal trip out to the Canyons, we would do 30-40 hours at low rpm’s before cruising back home. In the thousands of hours I put on various motors, I never saw any concerns attributed to this as the turbo vanes were clean, engines ran great and did not smoke. But I would never put the boat away from a trip with heavy usage at low RPM’s without spoiling it up to burn all the crap out and clean up the engine.
  13. JWY, Dec 21, 2020
    #13
    JWY

    JWY Senior Member

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    Better to spoil your engines than your children.

    (Sorry, I couldn't help myself.)
  14. Capt Ralph, Dec 21, 2020
    #14
    Capt Ralph

    Capt Ralph Senior Member

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    Something else you may need to think about;
    How will the boat ride / handle at slower speeds.
    Underwater designs for speed include small rudders and not so tall in diameter wheels.
    Not usually the set up you want for (LSD) Low-Speed-Displacement operation.
    Other boat items that change from fast to slow; open exhaust ports and E R ventilation.
    Also, bow angle my change. On some boats, LSD drives the bow low.

    I really think the later MAN, Cat, MTU and other computer driven engines will operate well at low speeds.
    My old TI Detroits (Pre DDEC) may not like it though. That is where the idea of running them up under load helps them out some.
  15. MLILIENTHAL, Dec 21, 2020
    #15
    MLILIENTHAL

    MLILIENTHAL New Member

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    That's a great point! I would plan to add stabilizers so the off-plane ride would be more comfortable but I hadn't thought about prop or rudder adjustments as well as the other items you mention.

    Thanks
  16. Capt Ralph, Dec 21, 2020
    #16
    Capt Ralph

    Capt Ralph Senior Member

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    Auto pilots sometimes have issues at slow speeds. Had to increase our rudder size to help us.

    What ever boat you look at, sea trial it well for handling and behavior at lower speeds. in all wind / current directions.
    Fill your surveyors in on what you are doing.

    Later engines should be able to offer some gph or even mpg at given speeds. Sometimes the best mpg is not the slowest speed.
    Again, trial her well at slow and higher speeds.

    On our old boat, exhaust harmonics drive me crazy under certain low rpm and loads.
    Bring a DBA meter with you also for your trials to help ensure things are in deed quiet while running slower.
    Our ole Bert is quieter and rides better at speed. Just can't afford the fuel burn.