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Greetings all,
Here's my dilemma. I am an LSRM-A working on an SLSA. I've got a somewhat older (~2007 vintage) Rotax 912ULS with a VDO-style oil pressure sensor and a TL Elektronik engine monitor. The pressure sensor is mounted directly to the oil pump housing.

This engine is showing fluctuating oil pressure. The pressure will fluctuate in and out of the acceptable range, as in 45, 52, 53, 102, 44, 23, 97... numbers in PSI.

There are several places I can think of to find the problem.

I've watched the video on this site on the subject, and it describes removing both the electric sensor and the pressure relief valve. The video leaves out what I consider to be VITAL information: Should you purge the oil system after either one of these services?

My money is on the sensor. I've replaced one of these sensors before (and performed the purge procedure just in case), but the only sensor available now is the Honeywell variable current styel sensor. That P.O.S. TL engine monitor has a password that nobody knows, so I can't get into it to change the settings. According to SI-912-020, the resistive-type VDO sensor "...is not suitable anymore." In context, this is a very vague statement. Does this mean that VDO sensors are no longer authorized for use on 912's, or that VDO sensors aren't compatible with the wiring for Honeywell-equipped engines? Can I legally replace this VDO sensor if I manage to find an identical unit, or must I install a Honeywell sensor? If I have to use a Honeywell sensor, it means a new engine monitor.

I doubt the issue is caused by engine vibration, but it's a plausible reason for the early failure. I'll have to talk with the airframe manufacturer about moving the sensor to the firewall. I have a temporary mechanical gauge, so I can do that check if need be.

So, to recap: Should I purge the oil system after removing the sensor, relief valve, or both? And can I install a new VDO sensor if I find one?

Thanks in advance,
Adam
LSRM-A CFI-SP
  • Re: Oil pressure problems--Total Whitewash.

    by » 12 years ago


    Hi Adam,

    I don't know what type of plane this is on, but my money is on either a poor ground and and my first choice is the VDO sender. I would check the grounding first since it's free then replace the sender. The sender type may depend on the type of plane. i.e. experimental, ELSA, SLSA. If it's an experimental then I would just replace the VDO original equipment sender.

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


  • Re: Oil pressure problems--Total Whitewash.

    by » 12 years ago


    Thanks Roger!
    It's an SLSA, an Allegro 2007 in point of fact.
    The sensor that's on the engine is a 2-pole sensor. I might try running the engine with this pole hooked to ground, I understand that's it's function. If it still acts up, I'll have to replace the sensor.
    Your answer suggests that using another VDO sensor is problematic on a certified plane. Could you clarify?
    Thanks again,
    Adam
    LSRM-A CFI-SP

  • Re: Oil pressure problems--Total Whitewash.

    by » 12 years ago


    Hi Adam,

    You have a VDO in place now, your system won't work correctly with the Honeywell and the bulletin doesn't say you can't use a VDO. I would replace what you have. An Allegro SLSA plane isn't a certified plane or engine. Several people I know have taken their Allegro to ELSA due to lack of support. You can remote mount the oil pressure sender to some place like the firewall and keep the vibration and heat away.

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


  • Re: Oil pressure problems--Total Whitewash.

    by » 12 years ago


    Hello,

    I do not like the VDO oil pressure sender. There have been several problems.
    1. they are based on resistance, i.e. two metal parts that rub against each other. This may cause stick-slip phenomena and when mounted direct to the engine block or firewall give fluctuating resistances due to vibration.
    2. there are a few guys I know that have oil leaking problems due to a faulty VDO oil pressure sender such that they have to land immediately.
    In fact Pipistrel have issued Service Bulletins on the matter: www.pipistrel.si stipulating that a Honeywell oil pressure sender shall be installed. The draw back is that you have to program the gauge for that or otherwise install a new gauge.

    Jan

  • Re: Oil pressure problems--Total Whitewash.

    by » 12 years ago


    And I don't really want to open that can of worms. I would rather use a honeywell sensor, but it would mean replacing the EMS.

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