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Thread: 912UL Preferred Oil Temp Sender Position

  1. #1

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    Default 912UL Preferred Oil Temp Sender Position

    G'day Everyone,

    I have a 912UL in my newly acquired Mk1V 1050 with a oil temp sender that is not working. It runs to a Westach 4 in 1 gauge. The sender is the type with the two wires coming out of it. The sender is located in the forward sump plug position instead of up next to the oil pump where Rotax intended them to go. Is there any advantages/disadvantages of just replacing the one in it's current position or should I try to source one that'll fit up next to the pump instead ?

    Can anyone give me a brief run down on how a two wire sender works vs a one wire sender. Neither of the two wires seem to run to earth, although I did have a little trouble tracing them among the other wires bundled up. I'm thinking this sender just has power coming in and the resisted power coming out to the gauge, no earth until in the gauge ? I'm guessing the two different types aren't interchangeable and are gauge dependent.

    Cheers, Glenn

  2. #2
    Senior Member Esser's Avatar
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    Default Re: 912UL Preferred Oil Temp Sender Position

    Most likely it is just earthed to the engine through the threads etc. I just have a VDO style sender for my oil temp. The first thing I would check is to make sure your sensor is in fact getting ~5V of power to it.
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  3. #3
    Senior Member HighWing's Avatar
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    Default Re: 912UL Preferred Oil Temp Sender Position

    From My experience. These senders are prone to failure. I have replaced mine several times and finally did some research and found a way to repair them. The two wires are to an internally mounted thermister that varies it's resistance according to temperature. What I believe is happening is that the manufacturer assembles the thermister and wires using heat shrink tubing prior to potting to insulate the wiring from the brass housing. Vibration can result in breakage of the solder joints because of the soft heat shrink surrounding them. What I did is paint the soldered up unit with epoxy to provide insulation on all the exposed wire parts, then after that cures I insert that into the housing and pour epoxy into the space to hold it all together. It becomes essentially a single unit - not prone to failure. If you want to fix your own, drill out the old stuff and the following link is the correct thermister. https://www.mouser.com/ProductDetail/527-2006-2786
    You can likely find them closer to home.
    Lowell Fitt
    Goodyear, AZ


    My You Tube Channel

  4. #4
    Senior Member efwd's Avatar
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    Wink Re: 912UL Preferred Oil Temp Sender Position

    Lowell, Are you AKA Macgyver?

  5. #5

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    Default Re: 912UL Preferred Oil Temp Sender Position

    Thanks for your replys fella's. Did check that I had power but the cause of my sensor failure seems to be as Lowell has described. My wires and surrounding plastic stuff had actually dropped out of the brass section a little way and were a slightly loose fit. I suspect it's all come adrift inside but I haven't actually yanked them out yet. I did try pushing them back up just to see if it would work but no.

    I had a look at a wiring diagram online for the sensors and it seems one of them does indeed run back to the same earth point as the gauge. I also was in contact with Westach via email to see if they could tell me which sensor I needed for the rotax but they required a little more info. They did mention that no other sensors were compatible with their gauges though. I suspect they have their own specific parameters for the thermister you mention Lowell.

    Another bit of research I did was on the actual thread type and sizes. For those interested, the spot for the original Rotax oil temp sender beside the oil pump is a M10x1.5 and the Plug Screw in the bottom of the crankcase where my sender is located is M16x1.5 I'm not sure on probe lengths to use though.

    Westach list 2 for the M10mm x 1.5. One with a 1"probe the other 5/8". Any idea how long the probe is on a genuine Rotax one next to the pump ? Strange thing is they don't seem to list one at M16mm x 1.5 which must be what I have.
    I do remember reading somewhere that someone stated that they were using the sensor for the Lycoming/Continental. Looked that up on Westach site and it's 5/8x18 THD which equates to M15.875 x 1.411 which I guess would screw right in but probably not perfectly and maybe that's what's in mine.

    So the question remains, where is a better location for the oil temp sender ? I'm leaning to just trying to replace the one I have in the sump just because it's already there but not if I can't get the proper thread. Maybe that's a good excuse to move it up by the pump. Or is there a better reason to move it up by the pump ?

    Cheers Glenn
    Last edited by Sandgroper74; 04-26-2018 at 12:42 AM.

  6. #6
    Senior Member HighWing's Avatar
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    Default Re: 912UL Preferred Oil Temp Sender Position

    Eddie,
    No, Not Macgyver, just an old guy that sort of understands two wires - especially those that have a + and - on them or black and red insulation. Put me in the back of one of the new flat panel things and I need to find the nearest teenager. I can't remember how I determined the Ohm rating, but was interested when searching that they were the only ones with the weird ohm value - 2.78 K Ohms. All the others were typical 100K, 10K etc.

    Glenn,
    If you want to fix your own, I do have one of the thermisters in my parts drawer that I could send you. If you are interested, PM me your address and it will be on its way.
    Last edited by HighWing; 04-26-2018 at 06:49 AM.
    Lowell Fitt
    Goodyear, AZ


    My You Tube Channel

  7. #7
    Senior Member efwd's Avatar
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    Default Re: 912UL Preferred Oil Temp Sender Position

    well Lowell, Im certainly not just referring to this latest post. You have done a lot of cool stuff so each and every time you show us something we haven't seen, I am (we are) always impressed.

  8. #8
    Senior Member HighWing's Avatar
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    Default Re: 912UL Preferred Oil Temp Sender Position

    Thanks for the kind words. I guess tinkering is my life and the Kitfox became my focus after a Mechanics Illustrated article featured the IV Speedster in 1992.
    Lowell Fitt
    Goodyear, AZ


    My You Tube Channel

  9. #9

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    Default Re: 912UL Preferred Oil Temp Sender Position

    Thankyou for your kind offer of sending the thermister Lowell, greatly appreciated. I can maybe source the correct one you listed from a local electronics store if I go ahead and decide to fix it.

    I think the way I'm going to go is to buy a sender with the correct thread that will fit up next to the oil pump where Rotax intended. I'm sure they placed it there for a reason. Westach does stock one I have narrowed it down to http://www.westach.com/gauge_images/399S10-1.5S.jpg

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    Senior Member Dave S's Avatar
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    Default Re: 912UL Preferred Oil Temp Sender Position

    Sandgroper,

    I had a similar experience to you having the oil temp sender die on our 912ULS, also with the 4 in 1 gauge. I very much like Lowell's idea of making up a better designed/secured one from parts.

    In a hurry to get back flying, I ended up buying 2 new units from Westach. The one I installed I modified by using red RTV to better save the wires from vibration. Also drilled a hole sideways on two adjacent flats of the hex for a safety wire. The second one went in my on board spares kit - figured if it dies once it can die again - probably a long ways from home.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

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