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  1. #11

    Re: Effects of Running Diesel at Low RPM

    So their called Pyrometers – thanks for the info. Could anybody recommend a good manufacturer of these for marine use? Sounds like a spot for 4 more gauges would also be necessary. I would be a little worried about drilling and tapping the exhaust manifolds for senders in fear they may crack with thermal expansion/contraction.

    I would hate to ruin my 1976 VT903s over trying to save a couple grand on gas.

  2. #12

    Re: Effects of Running Diesel at Low RPM

    Your manifolds may already have a port or ports machined and plugged for pyrometers. I'm not familiar enough with Cumaparts to know for sure, but many engines do have them.

    Also, you may not need two. It depends on your exhaust configuration. If you have a single turbo, and a single collection point you can do with one pyrometer.

    Another trick: if you do need two thermocouples (the sensor) you can wire them through a selector switch to a single gauge. Less holes in the dashboard.

    One manufacturer you can look at is Isspro. www.isspro.com
    --- The poster formerly known as Scrod ---

    I want to live in Theory, everything works there.

    1970 36C375

  3. #13

    Re: Effects of Running Diesel at Low RPM

    Frankly, I think the level of concern is unnecessary. When you consider DDs recommendations (above 900 RPM) it is clear that they were/are concerned about operating temps (water temp), not combustion chamber temp or turbo temp or any other temp.

    Certainly, it's not a bad idea to monitor all this if you are inclined to do so but IMHO, such monitoring will have a better chance of making you crazy/worried than anything else.

    The cooling system's job (though badly done on marine DDs) is to maintain the overall temp of the engine at an optimum level. If you run at higher loads, the cooling system is supposed to pull whatever heat away it takes to keep the engine at the proper temp. Same is true on the other end - it (is supposed to) restricts the amount of heat it pulls away to maintain the temp.

    Very few car/SUV engine ever operate at much more that a fraction of their load capability for their entire lives. Yet there is no issue with combustion chamber temps, turbo temps, etc. The only thing that is important is that the coolant temp - and therefore the engine operating temp - is within the design parameters for the engine.

  4. Effects of Running Diesel at Low RPM

    The purpose in having high enough internal combustion temperatures, as monitored by the turbo exhaust temps, is to insure reasonably complete combustion to avoid carbon build up...and subsequent wear on rings/liners etc.
    Pyrometers are very nice monitoring devices to have to continually test operating conditions, but an ocassional check of turbo exhaust temperatures via infra red thermometer is a reasonable alternative.

    DD may recommend 900 RPM on 8V71TI's, but when I run my 8V71TI's at 900 or 1,000 RPM for a few hours, when I speed up I notice more temporary smoke than when running in the 1300 to 1500 RPM range...And I get really bored at that slow cruise speed!!!! I don't know that its harmful, but I don't like the smoke feedback when I speed up so I don't run at those low RPMs much.
    Rob Brueckner
    former 1972 48ft YF, 'Lazy Days'
    Boating isn't a matter of life and death: it's more important than that.

  5. #15

    Re: Effects of Running Diesel at Low RPM

    Great trick to use switch so you can get away with one gauge. I do have one turbo per engine, I will look for thermo coupler port when I am on boat tonight. With the name “pyrometer” was able to find so additional good info in other post on this site and also google. Apparently pyrometers are a very good thing for truckers pulling big loads to monitor engine/fuel performance. From an older post I see they require no electricity other then the illuminating light for night time use and you can even get the one gauge to give you two simultaneous thermo coupler readings. Looks fairly inexpensive too – think $200 will get you a dual reading gauge and two thermocouples.

    I hear what Mike P is saying too – The cooling system, if properly designed, should keep the combustion chamber in a happy place. I am extra worried about my engines as I just bought her, plan on using her (did 20 hours over the weekend), and cannot really afford new engines for her. Unless I hooked alarm up to them as well, sure I will not be looking at them when they are reading a prelude to disaster. This is all good education, knowing factors that can mess up my engines (low engine coolant temp and unloaded running) and what I can possibly do to avoid it outside of running normal cruising speed. Atleast oil came down $4/barrel today (a trend that will hopefully continue with stronger dollar) making the latter more feasible and enjoyable.

  6. #16

    Re: Effects of Running Diesel at Low RPM

    They make a pyro with two needles in one gauge. You would only need one guage for each engine, but the gauge will show the temps for both banks on it. It is nice to see the temps on both side of a vee. If you see variations in temp from one side to the other it could be time to investigate to see if you have a bad injector, etc. None of this monitoring is necessary, but it sure is nice to have.
    Sky Cheney
    1985 53EDMY, Hull #CN759, "Rebecca"
    ELYC on White Lake--Montague, MI

  7. Effects of Running Diesel at Low RPM

    sgharford....
    a great diagnostic/preventive engine monitor device (to prevent engine failure) is a salt water flow meter...and helm alarm display. It's a pipe fitting insert with a flap valve and a magnetic switch put in the engine salt water flow line....when raw water is present, the flap opens...no alarm; if you lose salt water flow (bad impeller, clogged intake,etc) the flap closes and you get an instantaneous alarm...no waiting for the egine temp to climb before an alarm sounds...I got mine via West Marine, don't remember the brand name....

    Nice insurance when you a running in windy/rough weather or anytime you can't hear your exhaust sound.....
    Rob Brueckner
    former 1972 48ft YF, 'Lazy Days'
    Boating isn't a matter of life and death: it's more important than that.

  8. #18

    Re: Effects of Running Diesel at Low RPM

    Quote Originally Posted by SKYCHENEY View Post
    It is nice to see the temps on both side of a vee. If you see variations in temp from one side to the other it could be time to investigate to see if you have a bad injector, etc. None of this monitoring is necessary, but it sure is nice to have.
    Real engines (i.e. tugboat / ship propulsion, electrical powerplants etc.) have a thermocouple in each exhaust port and one at the turbo, all on a selector switch. Loads of great information. It just depends on how involved you want to get.

    You may get forced into it too. My 3208s have a dual plenum exhaust collector with one pyrometer port in each chamber. There is no single connection point.
    Last edited by Avenger; 05-30-2008 at 05:40 PM.
    --- The poster formerly known as Scrod ---

    I want to live in Theory, everything works there.

    1970 36C375

  9. Re: Effects of Running Diesel at Low RPM

    The issue to be concerned with on low rpm/low load operation on 2-stroke DDs is a condition called "wet stacking". Actually this condition can affect any diesel. I have only seen it personally occur on generators, where it is very common. In the army we used load banks to keep the generators loaded to at least 50% load at all times and never had a problem, until the army discontinued using load banks in the late 1980's. When we lost our load banks we had large generators that may only have 10-30% loading and we started having wet stack problems and cylinder wall glazing.

    Low combustion chamber temps results in incomplete combustion products building up and creating a sludge that increases in viscosity over time, it also builds up in the exhaust system. This sludge can cause head gasket failures, and in extreme cases broken rings.

    If you pay attention you should be able to avoid having problems, while it is not something to be alarmed about, you should still pay attention to the fact that it can occur under the right (wrong) conditions.

    My opinion on this topic from experience is that most of the real problems I have seen are from light loads at high RPM as found in generator applications. I don't really see this being a serious problem in a boat being operated at low rpm, because there is some load there, but I would stress that you should operate at an rpm to get to at least the low side of the temperature range.

    Maybe someone has actually experienced this in a similiar loading/rpm situation and can shed more light on this.
    Chris
    1973 48' Yachtfish
    "Boss Lady" my other expensive girlfriend.
    Follow the refurb at www.starcarpentry.com

  10. #20

    Re: Effects of Running Diesel at Low RPM

    Quote Originally Posted by sgharford View Post
    So their called Pyrometers – thanks for the info. Could anybody recommend a good manufacturer of these for marine use? Sounds like a spot for 4 more gauges would also be necessary. I would be a little worried about drilling and tapping the exhaust manifolds for senders in fear they may crack with thermal expansion/contraction.

    I would hate to ruin my 1976 VT903s over trying to save a couple grand on gas.

    Here you go
    http://www.hewittindustries.com/instruments.htm

    Brian

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