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Thread: Rotax CHT probes double duty.

  1. #1
    Senior Member Esser's Avatar
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    Default Rotax CHT probes double duty.

    So I am not using the two probes on the #2 and #3 cylinder since I am getting CHTs on all four cylinders via spark plug terminal. My question to you wise men, can I take those two probes and use them else where? Iím thinking of putting one in the rad for coolant temps which I think will work fine.

    The other one I want to put in the intake manifold so I can monitor temps in there. I know this probe probably wasnít designed for that in mind. These probes I think go up to 150C. Do they have a lower limit where they stop reading? My I take manifold shouldnít go higher than 90C... or should I just go buy a proper manifold temp probe and stop being cheap?

    If I do buy an off the shelf prob, I would probably get an automotive Bosch style one. They come with a two prong male plug. Iím assuming I can hook my one EIS wire to the other and the other to a ground and it will work just fine? Itís not proprietary Bosch stuff?
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  2. #2
    Senior Member PapuaPilot's Avatar
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    Default Re: Rotax CHT probes double duty.

    I don't see why they wouldn't work for an alternate purpose. Most likely any probe you get will be an alumel-chromel type.

    They should not have a problem reading lower temperatures. In the winter I usually look at my CHTs and EGTs to get an idea of the engine temperature before I start it. I have seen them reading accurately down around 30F. I have 9 probes that I can compare (CHT, EGT and OAT).

    I kind of like your idea, I can be a cheapskate too.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5, Continental IO-240
    Flying

  3. #3
    Senior Member jrevens's Avatar
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    Default Re: Rotax CHT probes double duty.

    With a ďglass panelĒ I assume you can program for different types of sensors and different ranges.

    I believe that those Rotax sensors are a variable resistance sender (RTD, thermistor, etc.). Iím not sure of the range, but they are surely designed for somewhere around a 12 to 24v max. circuit voltage.

    The two metal alloy sensors like Phil mentioned are thermocouples. They produce a variable voltage depending on temperature. They are also mainly used for EGT measurement in aircraft.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE

  4. #4
    Senior Member Esser's Avatar
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    Default Re: Rotax CHT probes double duty.

    Yeah these arenít the thermocouple wires. Looks like the probes go up to 150C. The VDO part number show a ďswitchĒ value of 90C so Iím wondering if that means it doesnít send below that?

    I think if I make these probes work the biggest issue will be they donít fit in an NPT boss since itís a metric course thread pitch.
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

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