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912ULS EGT overheating

in 912 / 914 Technical Questions 9 years ago

  • Re: 912ULS EGT overheating

    by » 9 years ago

    Hi,

    I just wanted to be clear in case I sent the wrong idea. When I said if these ideas don't work to call a larger Rotax service center, I mean't to get some fresh ideas from someone that works on lots of 912's on a regular basis, as opposed to a small shop that may not have that much experience with them. The more brains working on a problem the better. I didn't mean to imply that Roger isn't up to the job. On the contrary he seems like a sharp guy (who is also a nice guy), and spends lots of hours on here helping thousands of owners fix their engines. Sorry Roger if it seemed like I was slighting you.

    I also didn't want to cause any alarm with my statement about Mogas deposits in the fuel system causing problems. I think they very rarely if ever do when the gas is used in a timely manner. I was mentioning this as a more remote possibility if certain conditions are present. The Mogas deposits are due to impurities in the fuel (due to the economics of refining) and show themselves as staining in the clear fuel tanks and fuel lines (turning them from clear to brown on the inside). This is what turns them darker, and the older the fuel system the darker the staining tends to be if fuel cleaner is never used.

    When a weak concentration of fuel system cleaner such as Techron is used for the first time in a "dark" system it can partially dissolve these deposits (staining) and this can decrease the flow through a dirty fuel filter. The level of these deposits can be higher in the fuel system if the plane has had a period of its life where the Mogas was not used in a timely manner, and allowed to degrade in the fuel system. Ethanol blended gas seems to go bad faster than the ethanol free Mogas.

    Personally I use Techron to reduce this staining which makes it easier to see the fuel level in clear tanks, or in my plane the fuel level in clear tubing in the cockpit. Other brands may have a similar cleaning effect. I also think its important to use premium gas while using fuel system cleaner. Some cleaners such as Seafoam can reduce the effective octane of the fuel, and premium can give an added measure of safety against detonation.

    Kevin K.
    Sonex Jabiru 3300
      
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  • Re: 912ULS EGT overheating

    by » 9 years ago

    Hi Kevin,

    No issues here with me. I'm good.

    Years ago I did some research on the auto fuel staining of some plastic sight tubes and looked for a better alternative plastic tubing. For some fuels like aviation fuel the colors are just dyes.

    https://en.wikipedia.org/wiki/Fuel_dyes

    For our normal auto fuel the brown is just its manufactured color.
    Plastics and plastic tubing like many products are microscopically porous even though they don't leak fluid. Even some fuel hose seeps vapors, but not fluid. The brown stain in auto fuel will stain many things after long periods of constant exposure. After contacting several of the plastic tubing MFG's they all said eventually the brown staining would take place. Some plastics may be more susceptible. Nothing that we would normally use in our aircraft would be a good to clean the tubing and it should be replaced if you can no longer see through it (sight tubes mainly). The brown stain isn't a coating, but just a stain. Some fuel system components aren't susceptible to the staining.
    It can stain or darken some plastic fuel tanks over time depending on their composition.

    Is it worth trying to remove the stain and what would be a good product to do so? I don't know.

    On the Flight Design CT's they have plastic sight tubes. At about 2 years it's time for a change.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: 912ULS EGT overheating

    by » 9 years ago

    Hi,

    sorry for only replying now. I am out of the country and I am back on Friday. I will then have a look at what you suggested.

    Just to indicate what I already done:

    1. I checked the carb balance lines and carb mounting rubbers for leaks. All perfect.
    2. I checked the bowls for dirt. All clean
    3. Visually checked the jets. No restriction.

    My configuration is:

    1. Tank outlet about 300mm below carbs. I do have an electric backup pump.
    2. Plumbing from tank - tank outlet, fuel filter, gascolator, electric fuel pump, mechanical fuel pump, fuel flow sensor (2mm jet), carb distribution
    3. No return line to tank installed.

    What makes sense is that restricted fuel supply to both the carbs would cause this. Either fuel filter, gascolator or fuel flow sender. The fuel flow sender has a 2mm jet installed to get its calibration correct. Although I never had problems with it, and the previous flight was perfect, maybe something got stuck inside either the fuel filter or fuel flow sender, or tank outlet. The tank outlet is 6mm. I will check this and also remove the 2mm jet and install the 4mm jet.

    The flight was really short. I did engine runups to get the minimum takeoff temps. After about 20seconds after takeoff, at approx 5300rpm, the EGTs peaked and I immediately reduced power. It remained high while I did a low go-around to land ASAP. When downwind I reduced power to 4000rpm, after which the EGTs came down slowly.

    The CHTs and oil temp was still well in its normal operating temps. Oil approx 80C and CHTs 85C.

    I use 95 Unleaded Auto Fuel. I will also install the flow restrictor and a return line to the tank.

    Thanks for all your assistance and hints!!

    Just a video to show you what my aircraft looks like...

    [video]http://www.youtube.com/watch?v=KxQ01navhvE[/video]



    Jacques
      
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  • Re: 912ULS EGT overheating

    by » 9 years ago

    fuel flow with 2mm jets? how strange!
    A standard aircraft fuel flow has a in-line transducer with a turbine wheel so they do not restrict flow.
      
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  • Re: 912ULS EGT overheating

    by » 9 years ago

    "The fuel flow sender has a 2mm jet installed to get its calibration correct. Although I never had problems with it, and the previous flight was perfect, maybe something got stuck inside either the fuel filter or fuel flow sender, or tank outlet."


    Certainly a good place to check. I'm with Rob. Most transducers have a wheel inside with no restriction and there should be a filter upstream of the transducer. Does your 2mm restrictor have a filter prior to that jet?.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report
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