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914-F extremely high Oil Pressure on start-up

in 912 / 914 Technical Questions 7 years ago
When I initially start my 914-F engine, not hot restart, the oil pressure is extremely high. It pegs my VDO gauge. I let engine idle for 1.5 to 3 minutes for temps to come up a bit then slowly advance the throttle. The pressure then drops into normal range.
I run MoGas now, as I had trouble with coking in the turbo return line which caused all sorts of problems. So oil runs clean now.
Ideas on problem? The check ball and spring in the pump?

  • Re: 914-F extremely high Oil Pressure on start-up

    by » 7 years ago

    yes, check the pressure relief valve ball/spring/seat.
    take the spring out of the plug screw, rinse it out with carb-clean or break clean (to break the surface tension) and see what you have for shims inside. you may have to use pressurized air to get them out.
    Make sure you have the new plug screw (silver color)
    look up inside the pump housing, with a mirror, and check the relief valve seat is clean and has even contact wear.
    check the side of the spring for sharp edges (from rubbing on plug screw)
      
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  • Re: 914-F extremely high Oil Pressure on start-up

    by » 7 years ago

    Consider a faulty sensor. As I was informed by the german Rotx dealer, sometimes the sensors cause such indication. This relates to the old style sensors with big body (VDO). It may happen, that parts inside the sensor get worn and don´t move smoothly any more. Problems with the pressure relief valve would only cause overpressure of maybe 1 or 2 bar.
      
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  • Re: 914-F extremely high Oil Pressure on start-up

    by » 7 years ago

    Rule out the sensor first.
    However, it is unlikely that the sensor will vary with heat.
    Install a mechanical gauge in place of the sensor and view it at a cold start to confirm that the pressure is actually high.

    How cold is cold? 0°C is a lot different from 30°C.
    Temperatures at and below freezing naturally prouduce high pressures.

    When the pressure returns to normal, does it reduce suddenly like something unstuck?
    or does it gradually reduce in proportion to the temperature rise?

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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  • Re: 914-F extremely high Oil Pressure on start-up

    by » 7 years ago

    When I say a cold engine it is never below 35 degrees F. More typically 35-60 degrees F.

    When the pressure drops it is more sudden than gradual. Specifically I start the engine, within 5-8 seconds the Oil Pressure rises. The gauge goes to full maximum on the VDO panel gauge. I let the engine idle for concern of stressing bearings with over pressure. After a short warm-up, oil temp just a little below 50 degreed C and water temp around 60-80 degrees C, I slowly advance the throttle and at a point around 1,500 RPM prop speed the oil pressure will drop right into central of the operating pressure.

    Important to note: I am running MoGas not 100LL. I would never recommend 100LL on a 914. The lead buildup and 'coking' is very problematic. I've had to declare an emergency more than once due to 'coking' blocking the turbo oil sump and then blowing all the engine oil out the turbo bearing.
      
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  • Re: 914-F extremely high Oil Pressure on start-up

    by » 7 years ago

    What is your VDO gauge range (what is maximum pressure on your gauge)?
      
    Report
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