CHT probs, ring terminal type

I have a Subaru H6 that I always thought it would be nice to have/monitor CHTs. I thought the heads would have to be drilled and tapped and probes could be installed, but the risk of destroying the heads did not seem worth it. I don't know of any Subarus that run CHT probes.

Then I stumbled upon this type of CHT probe:


GRT and Dynon seem to sell ring terminal CHT probes for the Jabiru engines.

The Spark plugs sit pretty deep in the heads and a coil pack covers the hole of a Subaru so i'm not sure if they would even fit.

So....
1. Has anyone installed these on a Subaru?
2. used this type of CHT probe in another application?
3. do they work? (work well?)
4. being a liquid cooled engine, would knowing the CHT tell me anything different or useful?

Thanks,

Thermocouples

Hi Jeff,

I have CHT thermocouples in each cylinder bank in my airplane. I don?t think the ones pictured would work for your aircraft. The spark plugs are so deep and the plug wires would get in the way. Mine were installed by the builder who is a partner in KS Avionics. Since your engine is water cooled you just need to attach a thermocouple to any bolt or screw on the head. They could make you a couple of sensors or sell you the wire to make your own. The engine monitor can take inputs from thermocouples, you just have to calibrate it.

I have found them useful only when waiting for the engine to warm up for takeoff. Sometimes the coolant temperature sensor lags the rest of the engine due to a bubble where the sensor is. After the engine warms up, the heads are equal and run about 10 degrees cooler than the coolant.

-Andy

jcaplins said:

I have a Subaru H6 that I always thought it would be nice to have/monitor CHTs. I thought the heads would have to be drilled and tapped and probes could be installed, but the risk of destroying the heads did not seem worth it. I don't know of any Subarus that run CHT probes.

Then I stumbled upon this type of CHT probe:

GRT and Dynon seem to sell ring terminal CHT probes for the Jabiru engines.

The Spark plugs sit pretty deep in the heads and a coil pack covers the hole of a Subaru so i'm not sure if they would even fit.

So....
1. Has anyone installed these on a Subaru?
2. used this type of CHT probe in another application?
3. do they work? (work well?)
4. being a liquid cooled engine, would knowing the CHT tell me anything different or useful?

Thanks,

Click to expand...

Not very useful on a liquid cooled engine. Coolant temp will tell you all you need to know.

simpkinsona said:

Hi Jeff,
I have found them useful only when waiting for the engine to warm up for takeoff. Sometimes the coolant temperature sensor lags the rest of the engine due to a bubble where the sensor is. After the engine warms up, the heads are equal and run about 10 degrees cooler than the coolant.
-Andy

Click to expand...

Andy,
I took a another look yesterday, and it seems there is no practical way to install them considering the depth and the coil packs.
Since I have the GRT EIS4000, and unused CHT inputs, I may get a couple sensors with rings sized for a bolt on the heads. (and if they seem useless, then I suppose I can put them anywhere else and monitor the temp of whatever I want)

Do you have a photo of where they are bolted? Or maybe let me know when you plan to have the cowling off next, and I'll zip down there and look around?

rv6ejguy said:

Not very useful on a liquid cooled engine. Coolant temp will tell you all you need to know.

Click to expand...

Ross,

That is generally what I thought, but since Rotax, being liquid cooled, uses a CHT probe or 2, there might be something useful that I was missing.

----

And that brings up my next issue (and 'a' reason for wanting to know the CHT).... My engine seems to be running too cold. I've doubted the sensors, and and I've doubted the accuracy of testing the sensors. (this is also why I think maybe CHT sensors might tell me something), but here we go:

During cruise:
The engine temp sensor (ET) through the SDS reads 158F
coolant temp (H20), via EIS4000, reads ~160F
Oilt temp (OT) reads, EIS4000, reads ~155-165F

During hot summer days the temps will get to 190 during high power extended climbs. And oddly, even this time of year, will hit ~175 on final (full flaps, 15-18" MP, 2300 RPM).

For these 3 inputs to the EIS and SDS there is no offset or scaling factor for me to adjust. I've swapped/replaced sensors with no change in readings,
I've also used an aux input to the EIS, which I can calibrate the offset and scaling factor. Still, everything comes in at 160 degrees.

At one point I found the thermostat installed was for 160. I installed a 190 degree thermostat and thought my problems were solved... but nope, during cruise, the temps are still rock solid around 160 degrees.

So, If I assume my temp readings are correct, and I assume the thermostat is working (temps not fluctuating or overheating):
1. Why is the H20 and ET not stabilizing at 190F? (my Jeep is rock solid at 210 degrees regardless of outside temp or how hard the engine is working)
2. There is no thermostat or bypass control for the oil, that I know of. Could the oil be keeping the engine cold?

Temps

I?ll take a photo of the sensors next time I pull the top cowl off. You can check your calibration by immersing the sensor in boiling water. Just have to hook up a ground to the body of the sensor. My engine has a 170 degree thermostat and runs about 165 on cold days. Hot days it?ll get up to 220 or so in the climb, and stay about 180 in cruise.

-Andy