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Rotax oil temperature sensor


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hi recently i have noted that the oil temperature readings were getting to be too high in normal climbs.

 

The eng is a 912 S. I dont think its actually getting over hot. So i decided to check the gauge and sensor.

 

I checked the sensor resistance to ground whilst the engine was cold and had a reading of 860 ohms at 25 deg C. With the wire disconnected.

 

I compared this value with 5 other 912 engines and they all were near to 1000 ohms.

 

This leads me to believe that my sensor is lower than average and therefor the gauge will read higher by about 10 degrees ( 10% of 100 ) the sensor drops resistance as it gets hotter so it can only go down a max of 1000 ohms. Hence 10 %

 

I also noted that my gauge was the only gauge to move off the stop when the master was switched on.

 

Now heres my question. A new sensor has been quoted at about $ 400. Yes thats $400 ..

 

The 912 by the way has 3 of these fitted they are oil and cht x 2 they are the same sensor.

 

2 questions .......... is there a sensor available at a cheaper price anywhere?

 

And i am considering removing the sensor and testing it in hot oil with a thermometer . Has anyone done a similar test and what was your experience?

 

By the way this is the eng that had the brass rocker bushes, its running sweetly since the overhaul, this temperature issue has been brewing for quite a while, long before the brass rocker issue.

 

 

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Yep they are ntc . But i am not sure if all ntc sensors are the same , i would think that they might be given that there are many different gauges that use the rotax sensors.

 

 

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If you are only using one of the CHT sensors (most just use the hottest cyl) swap the CHT sensor to the oil pump and see if it makes a difference. My recollection is that they are VDO sensors as mark suggested.

 

Greg.

 

 

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If you are only using one of the CHT sensors (most just use the hottest cyl) swap the CHT sensor to the oil pump and see if it makes a difference. My recollection is that they are VDO sensors as mark suggested.Greg.

Yes! did that myself a couple of weeks ago. I actually swapped #4 cyl CHT and oil temp. Both read the same as before swapping, so I guess they're good.

I also have a spare fitted in # 2 cyl .

 

 

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Yes! did that myself a couple of weeks ago. I actually swapped #4 cyl CHT and oil temp. Both read the same as before swapping, so I guess they're good.I also have a spare fitted in # 2 cyl .

I

 

hi recently i have noted that the oil temperature readings were getting to be too high in normal climbs.The eng is a 912 S. I dont think its actually getting over hot. So i decided to check the gauge and sensor.

I checked the sensor resistance to ground whilst the engine was cold and had a reading of 860 ohms at 25 deg C. With the wire disconnected.

 

I compared this value with 5 other 912 engines and they all were near to 1000 ohms.

 

This leads me to believe that my sensor is lower than average and therefor the gauge will read higher by about 10 degrees ( 10% of 100 ) the sensor drops resistance as it gets hotter so it can only go down a max of 1000 ohms. Hence 10 %

 

I also noted that my gauge was the only gauge to move off the stop when the master was switched on.

 

Now heres my question. A new sensor has been quoted at about $ 400. Yes thats $400 ..

 

The 912 by the way has 3 of these fitted they are oil and cht x 2 they are the same sensor.

 

2 questions .......... is there a sensor available at a cheaper price anywhere?

 

And i am considering removing the sensor and testing it in hot oil with a thermometer . Has anyone done a similar test and what was your experience?

 

By the way this is the eng that had the brass rocker bushes, its running sweetly since the overhaul, this temperature issue has been brewing for quite a while, long before the brass rocker issue.

I don't know who quoted you the $400? They are $200 or close to that!

 

 

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Thanks for the replies.

 

Will do the swap as suggested. There is the spare unit on the front cylinder.

 

I undestand that these sensors are put in with locktight . If this is correct did you need to heat the sensor to get it undone.?

 

 

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As to the price i was quoted.... I went to the usual rotax supplier in Vic. I do have trouble hearing on the phone so its not impossible that i got it wrong but. She advised me that these were very expensive $370 + gst

 

If it was $170 + That would come in around 200. I will confirm by email to be sure.

 

Thanks

 

 

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Ok..... I rechecked the qoted price and i was slightly high. The quote for the 1 x 456180 oil temperature sensor is $333.78 + Freight $12.70 i guess that includes gst. So i was $50 too high. But still ouch or is that gouge.

 

 

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I did a test once with a rotax sensor with the resistance readings and it tallied very closely with the numbers in the VDO catalog. So my guess is if you can get the VDO sensor with the right length and thread you should be good. However, if you swapped two sensors and the readings remained the same, you should probably look elsewhere for your high oil temps on climb.

 

I have found on long climbs at cruise power, that the oil temp goes up more quickly than the coolant temp. I guess the load on the gearbox causes the oil temp rise, so maybe it's time to open the gearbox and have a look. Have you been checking the magnetic plug at the oil changes?

 

 

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image.png.7d4f3b377a580f52a46494e2f29f1bf1.png If this is the correct sensor for a 912 then someone is ripping us off.....

 

I did a test once with a rotax sensor with the resistance readings and it tallied very closely with the numbers in the VDO catalog. So my guess is if you can get the VDO sensor with the right length and thread you should be good. However, if you swapped two sensors and the readings remained the same, you should probably look elsewhere for your high oil temps on climb.I have found on long climbs at cruise power, that the oil temp goes up more quickly than the coolant temp. I guess the load on the gearbox causes the oil temp rise, so maybe it's time to open the gearbox and have a look. Have you been checking the magnetic plug at the oil changes?

yes there is nothing wrong with te engine , it is jut out of a very expensive overhaul, the gauge reads high when its cold ( checked against 5 other rotax 912 engines as a comparison ) pretty sure this is just a instrument ( sensor ) error.

 

 

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  • 2 weeks later...
Floods dont miss you....Try to buy 1 of the ignition modules....Someone up here recently had to get one $1400 Each....its bloody scandalous

New sensor arrived from the UK 7 days exactly from placing the order. $58 AU DELIVERED .Genuine VDO . Fitted easily test flown and no issues , need to wait now for summer to come back for a real test.

 

 

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That sensor, purchased from the local Rotax agent (via Floods) is NZ$370!!!!! I had to buy 2 for a second-hand 912S that I imported from the USA - it didn't have the sensors fitted. As for the ignition modules, we have had a few fail in recent times and I'm told you can only now get them in pairs - around NZ$3000! However one of our members who is an electronics whiz is planning to pull one apart and build them himself. He reckons the components wont cost more than a few dollars!

 

 

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I support local retailers when its sensible to do so. But this difference in price for the sensor cant be justified.

 

As for the ignition packs . I am a electronics guy as well so would be interested in hearing how he is going to atchiev this. It might not e as simple as all that.... But i have been wrong before.

 

There is a theory doing the rounds about the failures being caused by overheating after engine shutdown.

 

It does make some sense in that when the cooling air stops any engine heat will build up under the top of the cowl.

 

And thats where these packs sit . In my aircraft which has a hinged upper cowl it would be simple enogh to prop the cowl open after stutdown . Of course this theory cant be easily tested

 

As to the price of the packs their price doubled overnight about 2 or 3 years ago .why?? Who knows .. Not us thats for sure.

 

 

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I believe 80 degrees C is the limit for Modules and Regulator.

 

I have temp strips on both, that change colour over 82C.

 

Last summer that temp was never reached.

 

Always good to know...

 

 

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Thanks for that its interesting that they are 80 deg rated, designed to fail.

 

Have you thought to place some lower temperature strips to see how close you are getting to the temperature rating? If for example they are getting to 70 then with time they will depreciate . I guess we are getting off the original post topic here but these things being so expensive we should be coming up with a strategy to keep them running. Thanks again..

 

 

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I am still trying to get hold of the later version ignition module for the 912...the one with soft start so I can disembowel it. I have the older ones done but didnt particularly want to make old versions that can fail. I have upgraded a lot of the parts in the circuit but would much prefer the better new ones that dont seem to fail

 

The older ones fail due to heat and bad design. But to date I have not been able to find a faulty new one. The old ones were made by Ducati..the later series like I have on my engine are made by Motorini. If you have the older ign module on your engine you use the new module but do not enable the soft start. You can only enable the soft start on the later engines as they have a different set of timing on the flywheel pickups

 

 

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Thanks for that its interesting that they are 80 deg rated, designed to fail.Have you thought to place some lower temperature strips to see how close you are getting to the temperature rating? If for example they are getting to 70 then with time they will depreciate . I guess we are getting off the original post topic here but these things being so expensive we should be coming up with a strategy to keep them running. Thanks again..

No, haven't tried lower temp strips.

 

There is a theory they start to fail at low rpm initially when on their way out.

 

When starting on both mags and doing 3000 rpm mag checks this is not apparent.

 

As I have 2 individual mag switches, I can start on either mag (and do so) to make sure they are working right from start up.

 

 

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I am still trying to get hold of the later version ignition module for the 912...the one with soft start so I can disembowel it. I have the older ones done but didnt particularly want to make old versions that can fail. I have upgraded a lot of the parts in the circuit but would much prefer the better new ones that dont seem to failThe older ones fail due to heat and bad design. But to date I have not been able to find a faulty new one. The old ones were made by Ducati..the later series like I have on my engine are made by Motorini. If you have the older ign module on your engine you use the new module but do not enable the soft start. You can only enable the soft start on the later engines as they have a different set of timing on the flywheel pickups

Nice bit of info there. Any idea where in the engine serial numbers the soft start capability starts?

 

Im assuming that the capable engines will be wired for the feature or do they need to be adapted for the soft start to be enabled?

 

 

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No idea on serial numbers but the old ones actually have Ducati molded into them the new ones dont. You dont have to enable the softstart on your new engine when you wire it up if you dont want to. But because its there you would normally do it. This is why the same module can be used for old and new engines.

 

 

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