Rotax 912 CHT

[JUSTNUZZA]

What does Rotax recommend for optimum running CHT temperatures for a 912uls ? I know the max is 135.

 

 

[Downunder]

http://www.rotaxservice.com/rotax_tips/rotax_feed4.htm

 

 

 

[JUSTNUZZA]

Downunder, that's what I am looking for.

[microman]

I have a problem with the CHT in my Alpi (Rotax 912S). It seems that the gauge I mounted is incompatible with the Rotax sender and the readings I got (always in the green) were purely coincidental and bore no relation to the actual temperature. I need to either get another gauge which is compatible or use the gauge I have with a thermocouple under a spark plug. Anyone have any suggestions as to the best way to go? Another possible alternative is to get a gauge with a probe which would go into a hose from the radiator. That would give me an actual water temp rather than a cylinder head temp.

 

 

[OzBirdy]

Cht/ coolant temps, the cooler the better.

 

Aircooled barrels means you dont need bother with coolant thermostats.

 

Cooler is better efficiancy.

 

Just be sure you keep the oil temp regulated.

 

 

[cscotthendry]

Alpi:

 

You need to make sure that the sender on your engine is matched to the gauge. There are different types of temperature senders and some of them have different resistance / temperature coefficients.

 

You can usually check which type of thermocouple is in the sender by looking up the markings on the internet. To see if your gauge matches it do the following

 

Go to Jaycar and buy a 56 ohm resistor

 

Disconnect the wire from the temperature sender at the engine

 

Connect the resistor between the wire that you disconnected from the sender, and the engine crankcase or head.

 

With that resistor connected securely, go and turn the master switch on. Your temperature gauge should read somewhere around the 100 deg C mark.

 

If it is significantly different (like reading very low or off the scale) then your gauge doesn't match the rotax sender.

 

The Rotax senders are VDO parts and if you look at their data sheet available from their website, you will see that the Rotax sender is type C (calibration chart 2) which should have about 62 ohms at 100 deg C.

 

If the sender has been changed, or you suspect it is faulty, take it home and put it in some boiling water and measure the resistance with a multimeter. It should read about 60-odd ohms.

 

 

[Xavier]

Hi,

 

this document might help for the VDO Temperature sender used in the 912 :

 

http://www.vdo-gauges.com/media/instructions/TU00-0770-5104620%20Temperature%20Sensors_short_version.pdf

 

Xavier

 

 

[microman]

Thanks for that guys - really helpful!

 

 

[Kyle Communications]

Actually there is no water temp measurement on the Rotax. The sender unit is mounted in the head and no water runs through there it just sits inside a space in the head so it is actually the CHT you read from the sender

 

 

[cscotthendry]

Actually there is no water temp measurement on the Rotax. The sender unit is mounted in the head and no water runs through there it just sits inside a space in the head so it is actually the CHT you read from the sender

Mark:

It depends on the model of engine. The newest engines have different heads and the temp sensor is embedded in the coolant now. There is a service bulletin for this on Rotax Owner.com.

 

 

[Downunder]

I would stick with the rotax sender and get the correct gauge.

 

Stick with what is standard and normal with these engines.

 

Thermocouple under plug or different sender just opens a can of worms in regards to future problems/readings. (Including future aircraft ownership)

 

 

[Kyle Communications]

Mark:It depends on the model of engine. The newest engines have different heads and the temp sensor is embedded in the coolant now. There is a service bulletin for this on Rotax Owner.com.

Interesting I will go and have a look. Mine go into a empty space in the head. No water at all

 

 

[Kyle Communications]

http://legacy.rotaxowner.com/si_tb_info/serviceb/sb-912-066ul-r1.pdf

 

So for anyone with a factory built aircraft by the look of it you must put 4 new cylinder heads on your engine. I see it is mandatory so I suppose it is for all engines or really is it just certified engines?

 

 

[Ultralights]

there is a list of seruial numbers the bullitin is applicable to, fortunately my engine is not on that list..

 

 

[aro]

http://legacy.rotaxowner.com/si_tb_info/serviceb/sb-912-066ul-r1.pdfSo for anyone with a factory built aircraft by the look of it you must put 4 new cylinder heads on your engine. I see it is mandatory so I suppose it is for all engines or really is it just certified engines?

That doesn't tell you much, just refers you to sb-912-066 but from my reading sb-912-066 says if you have the new style cylinder heads, you need to change the instrument labels and temperature limits to match.

 

 

[Downunder]

http://legacy.rotaxowner.com/si_tb_info/serviceb/sb-912-066ul-r1.pdfSo for anyone with a factory built aircraft by the look of it you must put 4 new cylinder heads on your engine. I see it is mandatory so I suppose it is for all engines or really is it just certified engines?

I think they just want the serial/data plate changed to easily identify if these new heads are on the engine.

 

The Cylinder Head Temperature probe is now effectively the Coolant temp probe.

 

 

[crashley]

http://legacy.rotaxowner.com/si_tb_info/serviceb/sb-912-066ul-r1.pdfSo for anyone with a factory built aircraft by the look of it you must put 4 new cylinder heads on your engine. I see it is mandatory so I suppose it is for all engines or really is it just certified engines?

The service note says that if you fit the new type heads you have to change the green yellow and red temp ranges on the cht guage because on the new heads the sensor is now mounted in the water jacket

 

 

[nwarthmann]

Hi,this document might help for the VDO Temperature sender used in the 912 :

 

http://www.vdo-gauges.com/media/instructions/TU00-0770-5104620 Temperature Sensors_short_version.pdf

 

Xavier

Thank you for this info. I take from the Rotax 912 parts catalog that the temperature sensors for "oil temperature" and "cylinder head temperature" (CHT) are the same/interchangeable. At least on older engines where the CHT sensor is screwed into the cylinder head from below. The Rotax part number is 965531 (965530 in older part catalogs). It is an off-the-shelf VDO part. Has anyone figured out what the VDO part number of this sender/sensor is? Unfortunately, I do not have a sensor at hand to measure myself, I will need 3 and the Rotax price tag is 4 times above what a genuine VDO part would cost. Any help is greatly appreciated.

 

 

[cscotthendry]

Thank you for this info. I take from the Rotax 912 parts catalog that the temperature sensors for "oil temperature" and "cylinder head temperature" (CHT) are the same/interchangeable. At least on older engines where the CHT sensor is screwed into the cylinder head from below. The Rotax part number is 965531 (965530 in older part catalogs). It is an off-the-shelf VDO part. Has anyone figured out what the VDO part number of this sender/sensor is? Unfortunately, I do not have a sensor at hand to measure myself, I will need 3 and the Rotax price tag is 4 times above what a genuine VDO part would cost. Any help is greatly appreciated.

The sensors on the Rotax engine are the 150 deg model. I think it is either a 10 or 13mm thread (reasonably certain it is the 13). If you look through the VDO list, and look for the profile that looks like the Rotax sensors, I think there is only one that matches from the VDO list.