Erratic CHT sensor

[Warmi]

Hey,

Today I noticed one side CHT reading became erratic during flight . It was jumping now and then about 20-40 degrees back and forth pretty much instantaneously.

Here is a short clip of that happening :
https://www.youtube.com/watch?v=Lctv5uH ... e=youtu.be

I assume this is just a sensor ( it is about 8 years old or so and the engine ran just fine ) so the question is what would be the next course of action ?

Clean the spade connector ( I have the older design , placed under the cylinder ) ?
Check the engine ground ?

If I were to clean the connector , should I just clean it/scrub it or is there some recommended conductive lubricant I should use ?

Thanks

[drseti]

When sensors fail, they generally fail dead. Erratic readings are almost always intermittent wiring problems. By all means clean your spade connectors (I usually use Scotchbrite, and smear on a thin film of silicon grease afterward). The ground connection is often the first to go. Good luck - you can solve this!

[RBearden56]

There are two types of CHT sensors, Thermistor and Thermocouples. The thermistor is a temperature sensitive resistor that changes resistance with temperature. In a Dynon EMS system it is wired in series with a small resistor and the junction point is read by the EMS, these are prone to problems. The second type, the thermocouple is a bimetal sensor that generates a small voltage with respect to temperature that is read by the EMS, they are almost foolproof. The D120 has direct inputs for EGT and CHT thermocouples and are rock steady.
I had problems with my D120 using the thermistor and found the issue to be a bad ground for the system. Eventually I changed to thermocouples and was happy ever since.


Good luck with your repair

Randall Bearden
Sport Pilot
LSRM-A

[Warmi]

I have cleaned , greased and re-seated the relevant spade connector and haven’t had a single erratic reading in a week - so far so good.

Thanks

[fatsportpilot]

There are two types of CHT sensors, Thermistor and Thermocouples. The thermistor is a temperature sensitive resistor that changes resistance with temperature. In a Dynon EMS system it is wired in series with a small resistor and the junction point is read by the EMS, these are prone to problems. The second type, the thermocouple is a bimetal sensor that generates a small voltage with respect to temperature that is read by the EMS, they are almost foolproof. The D120 has direct inputs for EGT and CHT thermocouples and are rock steady.
I had problems with my D120 using the thermistor and found the issue to be a bad ground for the system. Eventually I changed to thermocouples and was happy ever since.


Good luck with your repair

Randall Bearden
Sport Pilot
LSRM-A

Which kind does Rotax use?

[Nomore767]

On my 912 ULS I’ve replaced the left side CHT sensor twice in 585 hours.
It would jump from normal to high then low triggering the yellow/red warnings.
Crimping/lubing the spade connector helped a bit.
In the end just bought a new sensor, life’s too short!

[ShawnM]

Which kind does Rotax use?

Rotax uses a VDO temp sender. It's the same part for the CHT and oil temp. VDO part number is stamped on the sender. 801/10/1. These are the senders in my 2007 Rotax engine.