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  • Re: 912ULS min Run-up temp issue

    by » 7 months ago


    I am to. A couple of years ago, I didn't believe the numbers. A local Rotax A&P physically checked it after I ran the engine for a while and He measured within 2 degrees of me. Since that time I installed a MGL Xtreme EMS and I suppose it could be wrong.

    A friend of mine who also flys the Rans S-19 in Greeley CO has been experiencing about the same temps.


  • Re: 912ULS min Run-up temp issue

    by » 7 months ago


    Exactly the same on a 914 powered SeaRey without a thermostat.  Below 35 degrees you cannot get it above 110 degrees at 2500 rpm.  I think a thermostat would be the answer based upon other SeaRey’s I have flown with one. 


  • Re: 912ULS min Run-up temp issue

    by » 7 months ago


    THANKS TOM


  • Re: 912ULS min Run-up temp issue

    by » 7 months ago


    Wayne Lindebaum wrote:

    the issue with cold oil in a Rotax 912 is more that it is too thick when cold and you get cavitation. Rotax is the only engine i have worked on that they suck / draw the oil through a long line and the oil cooler. you may note that when cold  you can drop the rpm and the oil pressure goes up. As it is an Aviation engine I run Rotax oils only. The cavitation can cause lifters to draw air  and lead to valve failure. I have had Rotax motors fail due to simple things saving a few cents  here and there. Valve failures destroying a motor at 600 hrs  take your time save your engine and life  a few min is not worth your engine or life.   

    "you may note that when cold  you can drop the rpm and the oil pressure goes up." This, I found was a symptom of old oil hoses on the suction side of the pump collapsing. The hoses will withstand very high positive pressures before bursting, but *negative* pressure will cause collapse relatively easily. Kinks and sharp bends encourage the issue.

     


  • Re: 912ULS min Run-up temp issue

    by » 7 months ago


    Bill Hertzel wrote:

    The problem with high revving at low temperatures is that the Oil Pressure spikes.
    To speed up the warm-up process, set the brakes and advance the throttle to ~60psi of Oil Pressure.
    As the engine warms up the pressure will drop and you can again advance the throttle to hold 60 psi.
    By the time you reach 50°C (~125°F) you will find you are Wide Open and still under 60 psi.
    Go Fly!

    This gets close to the key point. Within reason the oil temperature doesn't matter, nor does the pressure. *Flow* matters. Since the pump is constant volume, flow through it increases linearly with rpm. Shoving more gpm through increases the (back) pressure and with warm oil a standard engine will show about 10 psi per 1,000 rpm. When the system is sized to do this however and oil is cold, pressure builds much faster with rpm, hence the "spike". To protect the system against very high pressures, there's an oil bypass built into the engine case (not to be confused with the pressure bypass within the oil filter!). This will open at ~70 psi or so. So far, so good.

    But oil flow should increase with rpm. It will do so smoothly unless the bypass opens. Once the bypass opens, any further increase in rpm no longer increases flow. Cold, the OP will easily max out by 3,000 rpm. Advance the throttle in this condition and the oil flow @ WOT is about half what it should be, placing one's engine in danger.

    So, as you imply, measured OT is less important for warm up than the response of oil pressure with rpm. If one can get full or nearly full rpm without pegging the OP early, it's warm enough to go.


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