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raizo

Rotax 912 oil pressure fluctuations

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Good new from B Flood (BF) - they do not think there is anything significant in the small oil pressures drop I have noticed in my 912 since its recent 700 hr service.

 

BF have suggested that I check the actual oil pressure using a master (calibrate) oil pressure gauge. This I will try and arrange at the earliest opportunity.

 

BF mentioned several possibilities that may have caused or contributed to the small pressure drop -

 

  • ".........gauge starting to get tired, same with the oil pressure sender".
     
  • ".........Aeroshell Sport plus 4 in the Black bottle, the new Aeroshell in the Red bottle is a slightly different formula.....". which could cause or contribute to a small pressure drop
     
  • " ........spring in the oil pressure relief valve wears and this causes the oil pressure to drop".
     

 

I also queried the possibility of a defective oil filter as raised earlier in this conversation. BF's response was -

 

  • "We have never come across a defective oil filter".
     

 

My thanks to the excellent service from the BF technical staffer who responded to my enquiry.

 

My change from AeroShell Sport PLUS 4 Black bottle to Red bottle ties in very neatly with the observations made by BF

 

All food for thought and action where appropriate.

 

 

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Nice to know they've never come across a defective oil filter: imagine playing Russian Roulette with your otherwise correctly functioning engine every 50hrs???

 

So there's a failure budgeting exercise in there, and the traditional example goes like this:

 

Colour TV was introduced in the US before anywhere else, and the sets (incredibly complicated compared with B&W) were manufactured there and initially very expensive. To launch them, they offered strong warranties. They then experienced a large number of failures under warranty, and the cost pretty much sunk the US TV manufacturing industry.

 

The Japanese watched all this. They crunched the numbers on what would be a financially sustainable rate of failure. They then carried that number crunching right down to component level. And they then required their component suppliers to provide components guaranteed to have no greater than the required rate of failure.

 

I would suggest that anyone marketing an aircraft oil filter will be requiring the manufacturer to guarantee a maximum failure rate. And it will be a very very small number indeed.

 

 

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If you look at the Rotax oil system, you'll see that there are no high pressure oil lines outside of the engine. Remote mounting of the sender may relieve the sender of engine vibration, but it exposes high pressure oil outside the engine, with the resulting risk of oil loss if the line fails. Further, to isolate the sender from engine vibration, you have to mount the sender on the airframe, which requires elastic coupling somewhere and that usually means a rubber hose. Rubber hose + high pressure oil at 100+ deg = trouble IMO. I'm betting that's why Rotax have all the high pressure routing inside the engine.

 

Just as a kicker, Toyota found this out the hard way with high pressure oil lines with rubber connections driving the variable valve timing on their 200KW V6 engines. A failure of the line empties the V6 sump in about 10 seconds!

 

 

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If you look at the Rotax oil system, you'll see that there are no high pressure oil lines outside of the engine. Remote mounting of the sender may relieve the sender of engine vibration, but it exposes high pressure oil outside the engine, with the resulting risk of oil loss if the line fails. Further, to isolate the sender from engine vibration, you have to mount the sender on the airframe, which requires elastic coupling somewhere and that usually means a rubber hose. Rubber hose + high pressure oil at 100+ deg = trouble IMO. I'm betting that's why Rotax have all the high pressure routing inside the engine.

Just as a kicker, Toyota found this out the hard way with high pressure oil lines with rubber connections driving the variable valve timing on their 200KW V6 engines. A failure of the line empties the V6 sump in about 10 seconds!

Otherwise known as 'fix a problem and make a problem......'

 

 

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I used an oil line supplied by a hydraulic company 3500 psi and high temp rated to remote mount the sender I also covered it in fire sleeve so I think it should be fine

 

My oil pressure now is a lot more stable than before and am now complying with the VDO requirement that the sender must not be mounted directly to the engine

 

 

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and am now complying with the VDO requirement that the sender must not be mounted directly to the engine

While I'm not doubting that what you say is true, that is a very strange requirement, for a sensor NOT to be mounted to the equipment it is supposed to monitor.

 

 

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So sounds like stay with the black......what was that wesley snipe quote?...."always bet on black"

I didn't think they made the black one anymore? I thought the red bottle (with the same name as the old black) replaced the black bottle.

 

 

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While I'm not doubting that what you say is true, that is a very strange requirement, for a sensor NOT to be mounted to the equipment it is supposed to monitor.

I agree with you but until I moved the sensor the oil pressure fluctuated badly it has now settled down but still has fluctuations Direct mounting would be a lot easier and eliminate possible leaks

 

This is out of the dynon manual

 

Oil Pressure Sensor The EMS-D10 supports several oil pressure sensor installations. The Dynon-supplied sensor and the Rotax and Jabiru pre-installed sensors are the most common. DYNON-SUPPLIED OIL PRESSURE SENSOR First, mount the oil pressure sensor to a fixed location using an Adel clamp (see picture at lower right) or other secure method. The oil pressure sensor must not be installed directly to the engine due to potential vibration problems. Dynon Avionics’ sensor is supplied with a 1/8” NPT pipe thread fitting. An adapter might be necessary for some engines. Please see the manual supplied by the engine’s manufacturer. You must use appropriate pipe fitting adapters and ensure that the case of the sender has a connection to ground. This is critical for functionality. Crimp a standard #8 ring terminal onto the white/yellow wire from pin 6. Unscrew the stud cap from the threaded stud. Place the ring terminal on the stud and secure the cap down sandwiching the ring terminal. Due to vibration issues, never connect the sensor directly to the engine. If you use Teflon tape or other seal, ensure the sensor casing still maintains a good connection to ground. JABIRU AND ROTAX OIL PRESSURE If you are installing on a Jabiru or Rotax engine, your engine comes with a pre-installed oil pressure sensor. Prior to mid-2008, Rotax provided an oil pressure sensor with 2 tabs for electrical connection. In mid-2008, Rotax switched to a new type of oil pressure sensor (Rotax P/N 956413) with an integrated 2-wire cable. Connect this newer sensor according to the wiring diagram at right. Connect the red wire of the new sensor to EMS DB37 Pin 15 (12V). Connect the white wire of the new sensor to EMS DB37 Pin 6. Then, connect one end of a 200Ω resistor to pin 6, and the other end to ground. The Jabiru and both types of Rotax oil pressure sensors are compatible with the FlightDEKD180. Select the correct sensor type as described in the Oil Pressure Configuration section on page 5-9

 

 

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I believe that would be Dynon covering their a**. And I can't say I blame them: they have no control over what sort of motors, in what environment and condition, their equipment will be fitted to.

 

And it is not unreasonable to fit the sender remotely, provided that can be done without introducing other complications or problems.

 

Having said that, pressure transducers are also routinely fitted directly to all manner of equipment, where they work fine.

 

My experience in this area is with industrial refrigeration screw compressors of all sizes. They are noisy, they vibrate, and nowadays are often on VSDs, so the vibration frequencies will be changing. Typically we fit 4 X $300 transducers per compressor, measuring various gas and oil pressures. An average engineroom would have 4 to 6 compressors, so there would be 16 to 20 transducers.

 

As mentioned earlier, we deliberately oversize transducers in all applications to improve durability. So a suction transducer normally running at 2 bar (but may go to 5 when the system is off) is sized at 10 bar. And a discharge transducer typically running at 10 bar but may go to 15, is sized at 25 bar, and so on.

 

These are not expensive transducers, in fact they are at the economy end of the scale. My experience has been that we get a small but significant failure rate within the first few days. Thereafter, these systems run fault free 24/7 for decades, and we rarely replace a transducer.

 

 

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Just my 2 cents worth

 

I had oil pressure senders sent from Floods many years ago that where not the correct ones in ohm range I think from memory

 

I had fluctuating readings after installing a new one and after a while I got another one sent from them

 

It was no different so I was casually talking to my local auto elect one day and happened to have the Floods sender with me

 

He informed me it was the wrong one and got me the one he said it should be in ohm range (was a long time ago so I stand corrected if I'm wrong about ohm range) but it was something like that

 

But low and behold it was back to the way it used to sit with the one he supplied me

 

 

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I didn't think they made the black one anymore? I thought the red bottle (with the same name as the old black) replaced the black bottle.

AeroShell Oil Sport PLUS 4 (Red Bottle) is a direct replacement for AeroShell Oil Sport PLUS 4 (Black Bottle).

 

With regard to the formulation (Red/Black Bottle), I only have B Flood (BF) technical advisers comment that there has been a change.

 

It would not be the first time there has been a packaging change for an identical product, however I am inclined to go with the BF advice on the matter.

 

 

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Originally the aero product was the same as superbike 4, but some want the "comfort & assurance" of having an oil specially for an aeroplane. I'm NOT saying they are identical, but if someone had Superbike 4 in their Rotax it wouldn't scare me, particularly, unless it was a two stroke. Nev

 

 

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Anyone got a Rotax "Keller" oil sensor?

 

I'm interested to know the Keller part number.

 

 

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Id almost guarantee in 95% of cases its simply a faulty sensor or a faulty earth. The earth is generally easiest and cheapest to test or fix.

 

 

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You must be upwind of a fume trail, then there is the gap of safety you need. Nev

 

 

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Finally got the chance to use a borrowed "Master" oil pressure gauge to check out my system.

 

Master gauge has analogue dial face at one end of a short flexible oil pressure pipe and selection of screw adaptors at other end for connecting to engine oil pressure reading port.

 

  • Removed oil pressure sensor.
     
  • Screwed in Master gauge fittings & secured gauge on top side of engine.
     
  • Unable to see gauge from cockpit
     
  • Volunteered eldest son to read gauge at 2000, 3000, 3500, 4000 & 4500 RPM.
     
  • Secured aircraft to immovable object and applied wheel brakes.
     
  • While hand "burping" the engine, noted oil pressure rise to approximately 10 psi (good sign) as this is close to the minimum oil pressure of 12 psi Rotax requires for an engine at idle.
     
  • Commenced extended ground run to warm system before taking readings.
     
  • Cold day - 14.3 degrees C
     
  • Even after many minutes @ 2-3000 RPM & two WOT cycles, only able to warm engine Oil Temp to 60 degrees. Heads to 70 degrees
     
  • Commenced readings
     
  • 2000 RPM oil pressure readings fluctuating too much to be meaningful
     
  • 3000 RPM 45 psi
     
  • 3500 RPM 45 psi
     
  • 4000 RPM 45 psi
     
  • 4500 RPM not read - prop blast too strong
     

 

I think my oil pressure falls well within the Rotax requirement of 29 - 73 psi above 3500 RPM.

 

My "el cheapo" Speco oil pressure gauge usually reads 30 psi in flight - Engine temperatures would be in the normal range (not as for the test) so the Speco is probably under reading by about 10 psi (allowing 5 psi drop for hot oil) . I think I can live with that.

 

You may also be interested in:

 

  • My oil pressure sender has no legible markings of any kind. I believe it is the original one fitted to the engine in 2000/720+ operating hours ago & still functioning.
     
  • I am informed that Shell has placed some sort of a stop on sales of any remaining AeroShell Oil Sport PLUS 4 (Black Bottle). All aviation oil has a finite shelf life, any remaining stocks would likely be past its "use bye" date.
     

 

 

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Certified (release Note) oils for Aviation use do have a shelf life. It's pretty conservative. Anything suitable for the 912 would be ok for motorbike with engine-gearbox integral . You might be able to get some TIMEX oil stocks cheap if you ring around.. Nev

 

 

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Does anyone know where I can buy the VDO oil pressure sender as a reasonable price? That is what my 912 has fitted. thanks.David

Does it have the brass anti vibration ring? Not sure if you can get those anymore.....

 

 

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Just for anyones info in case it helps someone else in the future.

 

We were getting a few fuel and oil pressure alarms recently. The pressure would dive and then come back up. We tested fuel flows and pumps extensively, checked all lines, checked oil systems. Checked ground terminals. Nothing found.

 

Battery which is supposed to last 15 years (lol) was getting tired on cold mornings, so we decided to replace it. Wires are soldered to battery. While pulling back heat shrink on terminal and wire the - wire came off. It definitely wasn't loose or unattached, but it was significantly weaker than the + attachment.

 

We proceeded to install new battery. Aircraft starts perfect and all alarms have ceased.

 

Me thinks perhaps the solder had begun to crack and the slightly poor termination was causing the occasional alarms. Strangely they only occurred during late warmups or climb out. or possibly the battery was actually dying and causing the alarms.

 

 

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