I have a Kitfox model 6 powered by a 100 hp Rotax 912ULS.  The engine has about 800 hours on it.   Right after a routine oil change my oil pressure went from a steady 55-60 lbs to a slow descending condition.  Meaning that right after start, the OP would slowly roll down to about 25-30 lbs (in the yellow).  Since the only post-oil change variable was the filter, I figured that it was bad.  I hadn’t split the old filter yet so I put the old one back on and tried it out …



Same problem.


So I put the new filter back on and pressed on.   I figured the next best course of action was to put a mechanical gauge on just to see what the engine was actually putting out.  I did that and it was showing its normal 55-60 lbs.  Relieved over the fact that I had an indication problem (so I thought), I went to this site and read numerous posts and concluded that it was the sensor. Several posts said that 97% of the time it IS the sensor.  My sensor had 800 hours on it so I figured that it was time.  The sensor and gauge were both manufactured by Westech.  The gauge is a 4-1 (OP, OT, CHT, EGT).  Westach was slow in responding and after some time they ended up sending me the wrong sensor.  After some back and forth phone calls  and about a month of waiting for a replacement, I installed the new sensor and tried it out.  $269 dollars later …


Same problem.


Not wanting to deal with Westach again, I left the new sensor on and concluded that it must be the gauge.  So I found a local (east coast) company to diagnose it.  I packed it up and sent it over to Keystone instruments in Pennsylvania.   After another painfully long process they got back to me and said that they bench tested it and that I had a good gauge.  “Can’t find a problem”.   Another month and $175 dollars later …


Same problem.


Well I figured the last piece of the puzzle is the wiring.  So I pulled the protective covering off of all the wiring for the gauges.  I ended up finding some connectors hidden under the wiring protection that were questionable.  I redid the connections and made sure that all of the connections were tight on the back of the 4-1 gauge.   I also put a meter on all wires to see if the signals were being transferred from sensor to gauge.  Everything checked out.   Kicking myself in the arse for not doing this first, I jumped in and fired it up ….


Same freakin’ problem  ...


My hands are in the air.  I have no idea.  I thought that I might try to “tee” the mechanical gauge on it again and compare the two gauge indications side by side. I guess the only benefit there would be the re-verification of actual oil pressure. I guess I’m just fishing and I just don’t know where to go from here.  It doen't act like a bad ground and the drop seems to happen when the oil temp starts to rise / oil viscosity is lowered.  All other engine indications (OT, EGT, CHT) are normal.


Any help / input is very much appreciated!

  • Re: Low Oil pressure

    by » 5 months ago

    Exactly what model guage do you have? I went to there site and they have a trouble shooting btton for the 4 in 1 guage. The pressre senderfor oil pressure is a voltage type. 0 to 80 psi 0 to 5Volts. You could hook the sender to a air compressor and increase pressure and verfy the corresponding output voltage. If you have a adjustable DC power. supply you could vay DC voltage in to the pressure input on the guage to test it. If they check out good then its your wiring. Use Westechs schematic and wire oil pressure seperate from the harness.

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