Rotax 912 Oil Pressure Sensor Problem

[mak]

I have experienced big fluctuations in my oil pressure readings lately and after some research it seems as if it is a common problem with the Honeywell sensors on the 912’s. The oil level was well within the limits, but not to max. I filled the oil to max and then readings were without the big fluctuations. I would like to know if anybody else has experienced this and also any suggestions on a suitable alternative sensor.

[Rudix]

I have experienced big fluctuations in my oil pressure readings lately and after some research it seems as if it is a common problem with the Honeywell sensors on the 912’s. The oil level was well within the limits, but not to max. I filled the oil to max and then readings were without the big fluctuations. I would like to know if anybody else has experienced this and also any suggestions on a suitable alternative sensor.

Hi!

I had an oil pressure sensor fail on a 912 recently, initially the pressure started fluctuating and then it went right off the scale on the high side. I started looking for a spot to land but as there was no other indication of a problem and no oil pipes bursting I flew home going from landing spot to the next.

It turned out to be the sensor that failed, a quick replacement and all was well. The one on my 912 was a VDO sensor that I replaced with a VDO unit from Midas, works fine!

The fact that your readings were normal after filling the oil to max might be something different, maybe the oil is foaming and some bubbles were sucked into the system?

Regards,
Rudi

[Wagtail]

Good morning Marius,
We have had similar issues with the senders on a few other engines. My suggestion is to bring her in so we can connect the Calibrated mechanical gauge and first verify the condition of the actual pressure signal before changing the sender unit.

Regards
Johan

[Splinter]

I remember a story about our late friend Straydog that had erratic pressure readings on his 912s while flying over the Drakensberg! He fixed the problem by placing a piece of tape over the reading and the flashing red light! What a boy! THIS FIX IS NOT TO BE ADVISED!

ZU-RED

[Morph]

It turned out to be the sensor that failed, a quick replacement and all was well. The one on my 912 was a VDO sensor that I replaced with a VDO unit from Midas, works fine!

VDO have various sensors. The 912 has a max bar of 7. Use the sensor with the 0-10bar range, readily available at any Midas


360-004 VDO Oil Pressure Sender 150psi / 10 bar

[mak]

Rudix / Morph

Thanks for the response. Will the wiring for the Midas VDO sensor be the same as for the Honeywell? Read somewhere that the wiring is quite different.

Splinter, if this doesn't work can you please send me the specs for the tape, sure I could figure the size out to cover.

[Rudix]

It turned out to be the sensor that failed, a quick replacement and all was well. The one on my 912 was a VDO sensor that I replaced with a VDO unit from Midas, works fine!

VDO have various sensors. The 912 has a max bar of 7. Use the sensor with the 0-10bar range, readily available at any Midas


360-004 VDO Oil Pressure Sender 150psi / 10 bar

Yes, that is the one I used, btw, it is the same one that is used on the Jabiru engines.

[Morph]

Rudix / Morph

Thanks for the response. Will the wiring for the Midas VDO sensor be the same as for the Honeywell? Read somewhere that the wiring is quite different.

Splinter, if this doesn't work can you please send me the specs for the tape, sure I could figure the size out to cover.

The VDO is a single wire solution, using the engine earth as the other half of the circuit. What gauge are you using?

[mak]

Morph

I am using the MGL Odyssey panel.

[Morph]

No problem then,

You will find the Honeywell, if it has 2 wires is probably wired one wire to the MGL and the other to earth

just use the MGL link, the engine earth will be the other wire. The MGL uses an RDAC for all the wiring. This only has one input for the oild pressure sensor

check my Aircraft wiring diagram below. The black (labeled white) wire goes the the top right of the engine and the oil pressure

[mak]

Thanks Morph

[Thatchman]

You can buy either the two or single terminal VDO. I just replaced the one on my 912 with a two pin.

You can also buy it from Comet for about R1088.....or cheaper elsewhere.

[tigger_na]

Cheaper elsewhere for me, please. My VDO oil sender unit also broke, giving wildly erratic readings. Luckily I had previous experience with loose instrumentation cabling and decided to limp to the airport instead of making a precautionary landing. My life, so extended, was made miserable by VDO prices, so instead of forking out a thousand bucks for a new sender unit I bought an EQUUS sender unit for 80 bucks and spent the R920 so saved on fuel. The EQUUS also has a 1/8-27 NPT thread, but only a 0-7 bar pressure range, versus the VDOs 0-10bar. Since 7 bar is the maximum allowable oil pressure on a 912 UL, this is acceptable, for me at least.

Unbelievably EQUUS is not able to provide calibration data for their oil sender unit model 9832, so I checked the resistance versus pressure by connecting the sender to a compressor and recording the resistance readings at various pressures. The results are below. Please bear in mind that the calibration was done with backyard (not calibrated laboratory) equipment. It is evident that, if the EQUUS is used as a straight drop-in replacement, your deviation in the relevant range 2-5bar range will be a maximum of 13%, which is really good enough for me. My MGL Odyssey allows me to define any linear pressure-resistance characteristic, so the error of the EQUUS drops to below 8%. Even better.

[tigger_na]

Rudix, just FYI, the Rotax 912 family has a pressure relief valve on the oil pump. The pipes carrying oil to and from the engine carry no or negligible pressure, so you'd not have bursting pipes in case of high oil pressure anyway. A pressure reading above 5 bars (up to 7 bars with a cold start) almost always points to faulty instrumentation. Rotax advises a precautionary landing for low oil pressure, nothing for high oil pressure.

(Obviously there is a direct relation between high oil pressure and pucker factor, which is just something you have to live with.)

[Learjet]

Hi mak,
I recently experienced the same and replaced the VDO on my 914 - apparently the Honeywell sensors are now made in China and are poorer quality - coincidentally a couple of us gyro owners found that the sensors started playing up not long after we switched oils from the old (discontinued) Shell Advance VSX to the replacement Shell Advanvce AX7. Coincidence?