Oil psi drops the higher I climb

by Darryl Zubot in 912iS Technical Questions 6 years ago

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Re: Oil psi drops the higher I climb

by Roger Lee » 6 years ago

Roger Lee

125 5.12k 4.53k

make sure that this oil pressure change does not follow a throttle change. I have seen this and it may not be pressure, but a poor ground. My first time troubling shooting this many years ago took hours and even though there was a ground it was weak. As soon as I bypassed the old ground and connected a new one all issues went away with changing oil pressure.

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

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Re: Oil psi drops the higher I climb

by Bill Hertzel » 6 years ago

Bill Hertzel

13 1.95k 7.96k

The symptoms indicate a restriction on the suction side of the Oil Pump.
Assuming the Hoses are OK...
Did you confirm that the Metal pickup tube in the Oil tank is not restricted?
Have you confirmed that the dished metal plate at the bottom of the Oil tank is oriented correctly?
It should be Concave side Up like a bowl.
Not Dome side up. That could partially block the pickup tube.

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

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Re: Oil psi drops the higher I climb

by Darryl Zubot » 6 years ago

Darryl Zubot

2 16 2

Roger Lee the oil pressure does fluctuate with throttle change, but I installed analog gauge and it indicated the same thing so it’s not a sensor indication error. Bill I will check my oil tank out next oil change to confirm this isn’t the case.

I’ve now installed the new Franz thermostat that bolts onto radiator. This reduced oil lines by over 5 feet! So I now have 40 psi at 10,000’. This increased oil pressure by 10psi by reducing amount of resistance in the system. I still get the funky oil pressure change with throttle, when I reduce rpm to 4000 my oil pressure rises to 50-55 instantly.

My next issue now is to reduce oil temps, with this new thermostat my oil temp is now always above 110°c. I took temperature gun to radiator after an hour long flight and the oil radiator was 20°C at bottom, 50°c at top. I am thinking this thermostat is not opening up properly, it’s supposed to open at 87°c. So this is also affecting my oil pressure now with the high temps.

22B8DE01-7849-40D3-8FF2-32452972A347.jpeg (You do not have access to download this file.)

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Re: Oil psi drops the higher I climb

by Roger Lee » 6 years ago

Roger Lee

125 5.12k 4.53k

Hi Dzubot,

Flight Design started using those for a few planes. I had one guy in the shop that had one and he complained about high oil temps. The bends in the tubing is somewhat flattened and narrow which slows the oil flow. I removed it and went back to just hose and his temps dropped 20F. He's still flying it that way.
The 10 psi increase may be due to narrow metal tubing slowing the flow????
Usually when I see oil pressure drop with rpm increase and then go back up when you get down to maybe idle rpms I have found several times a poor ground was responsible. My meter would say I had a ground, but when I by-passed that ground and installed a known good ground the pressure fluctuation went away. You might take a long wire with alligator clips on the end. Attach one end to a know good ground and the other all the way up at the back of the instrument so you basically by-passed the original ground. This is how I have found poor ground.

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

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Re: Oil psi drops the higher I climb

by Darryl Zubot » 6 years ago

Darryl Zubot

2 16 2

Roger,

Rotax sent me a replacement thermostat to try and same thing, high oil temps. So either they have a bad batch of them or it just doesn’t work well. I would think the oil radiator should be warmer then 40°C when my oil temp is 110°c. The oat here in Edmonton, Alberta is now 0°c and my oil temp is around 110-115°c. There’s no way it should be that warm if this thermostat worked correctly.

We think the increase in oil pressure was because this thermostat reduces the oil lines in the system, which reduces its resistance. My personal feeling is the hydraulic prop on this engine is too much for the oil pump, can’t keep up, so having less oil lines reduces the amount the oil pump has to work to maintain pressure in the system. The higher I climb the harder the prop has to work, and oil pressure drops because it can’t keep up. That’s just my thought, makes sense because I will reduce throttle at high altitude and oil pressure rises. It’s at least acceptable now with the reduced oil lines but now with high oil temps this doesn’t help my oil pressure any.

I installed an analog oil pressure gauge and it showed the exact same readings as the electronic one so it’s not the sensor......

Very good to hear I’m not alone with high oil temps with this thermostat. Not so easy for me to go without a thermostat, we fly in -30°C weather here in winter and I fly over the mountains so I can take off with +30 and go into -10 on some flights.

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