97 Shamrock 246 w/ Yanmar 4LHSTE

Discussion in 'General Conversation' started by jonstr, Aug 25, 2020.

  1. jonstr

    jonstr New Member

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    Jul 2, 2017
    Hello everyone,

    Thanks in advance for any help you may offer.

    I have a 97 Shamrock with Yanmar 4LHSTE. 230hp. I am down on top end speed and acceleration.

    I have had many services done, including injectors, heat exchanger and turbo replaced. Since the turbo replacement I have not been able to achieve the 40mph I did before.

    The prop is pitched at 18 degrees with a minor cup and was just serviced as well. The bottom is clean.

    At this time I have trouble reaching even 30mph with full tanks. I have weighed the hull looking for water saturation and found none.

    I have checked the turbo psi output and have only been able to measure 20psi WOT while the manual stated 30psi max output. However, I am able to achieve the full 3300rpm.

    Prior to the turbo replacement, the turbo would kick in at 1800rpm. Now it kicks in about 2200rpm.

    There is not vibration, fuel economy is still good. Just not performing the way it used to. I always thought twist is twist regardless of how you got there. I'm at 3300rpm WOT. Am I wrong on this account? I have not checked fuel injection timing or pressure.

    Any other ideas or has anyone seen this before?

    Thanks for your input.

  2. Fish Witch

    Fish Witch Well-Known Member

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    Apr 1, 2008
    Anchorage and Seward, Alaska
    Who did your turbo work? Sounds like you got a turbo for the 4LH-DTP. Do you have a parts manual for your engine to check you got the right one? You should get to 30 psi at WOT. 20 is what I get at normal cruise with my 6LPA-STP
  3. crhodes

    crhodes Well-Known Member Supporting Captain

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    Aug 26, 2003
    Southport, NC
    Is this boat kept in the water? If so, it doesn't take much fouling to drop performance like you mentioned. In my area it would only take 3 weeks if antifouling was weak on prop/rudder, etc. (This said from experience - couldn't plain off.)
  4. Bach Wilson

    Bach Wilson Well-Known Member

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    Sep 16, 2018
    Is a 246 really capable of 40? That would seem considerably faster than most accounts I have read online.

    3300 RPM Says to me that your making all the rpm you need. Boost is a function of engine load. If it does not need 30psi, it will not make it. It it was falling short on RPM and boost then we have problems.

    (I am aware I over simplified that and will get beat up on it)
  5. saltwaters

    saltwaters Active Member

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    Aug 14, 2003
    Actually, all yanmar tachs read 100 rpm high. If it says 3300, the engine is at 3200 rpm. You can verify this by buying a phototach. Yanmar (all marine diesel mfgs) recommends the engine reaches max rpm plus 50 - 75 rpm when fully loaded (full fuel, full water and all of the equipment you take with you)

    Your engine is over propped.

    Yanmar has a procedure to clean the air side of the after cooler. Did the tech do this?

    The process is done without disassembling the after cooler housing. You get a small spray bottle and put some Dawn dish washing soap in in. Fill with water. Take the boat out and bring the engine up to operating temp. At cruise speed, (2900 - 3000 rpm), you slowly spray the soapy mix into the compressor side of the turbo. Spray the whole bottle. With a clean bottle, spray deionized water through it. It takes two people, one running the boat while one sprays the mixture in the turbo.

    This seems like an odd thing to do but it's in the Yanmar manual. Ask your mechanic about it. He should know about it. I did it on a Yanmar 4LH-STP and to two Volvo TAMD40A engines. Of course, proceed at your own risk.

    Back to low boost. You have a boost gauge, which is good. If you have a rebuilt turbo, it should be making proper boost. The tech that did the work should be able to fix this, if it's isn't a clogged after cooler.

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