CHT differential greater than 100 degrees in cruise

[kortopates]

3 hours ago, Buckeyechuck said:

https://https://www.aircraftspruce.com/catalog/pnpages/2856.php?gclid=EAIaIQobChMI1pqP56Wu8wIVZAp9Ch1gJwk2EAQYAiABEgJIJPD_BwE

This is the Insight piggyback thermo couple probe. JPI used to make this in a type K. My avionics guy has installed them.  A friend has one in his Bonanza. Much more accurate than the ring under the mounting boss. 

Yep, I used the JPI version adapter probe back in the days of the 830. Its the most accurate non-standard CHT probe option with the  units not approved for primary to work with you OEM CHT probe.  

[PT20J]

4 hours ago, Buckeyechuck said:

https://https://www.aircraftspruce.com/catalog/pnpages/2856.php?gclid=EAIaIQobChMI1pqP56Wu8wIVZAp9Ch1gJwk2EAQYAiABEgJIJPD_BwE

This is the Insight piggyback thermo couple probe. JPI used to make this in a type K. My avionics guy has installed them.  A friend has one in his Bonanza. Much more accurate than the ring under the mounting boss. 

OK, Now I see what you mean 

It seems very unusual for a ring thermocouple mounted at the cylinder well to read so much different than the bayonet. Spark plug ring thermocouples read higher than the well location because the spark plugs are hotter than the well. The surface of the cylinder head at the well location is cooler than the well, but it shouldn't be 80 degrees cooler. Mine was about 20 F cooler (M20J, IO-360-A3B6).

If it were mine, I would first check that the ring thermocouple is accurate. It should read the same as all the others when the engine is cold. You could put it in boiling water to test it at a higher temperature. Also, I might check that the ring terminals are tight without corrosion and that the star washer is between the terminals, and that the wires are not reversed.

Skip

[Buckeyechuck]

I checked the ring against factory bayonet up to 212 (cup of boiling water with cup heater). Both agreed as much as I could tell from the poor scaleability of the factory gauge. The only thing I can tell is this is a newly overhauled engine. Maybe paint and non even surface right at the gasket seat are interrupting good heat transfer. I tried to clean the surfaces and remounted with a new crush gasket, but no improvement. The ring terminal is against the cylinder. 

[PT20J]

My installation was on a factory rebuilt, so similar situation to yours and the ring was only about 20 deg less than the factory gauge which JPI told me is about average. It’s a pain, but you might try moving the ring to another cylinder and then you could compare two digital readings on the same cylinder.

Skip

[carusoam]

Chuck,

I was not able to get your link to work…

Did I miss something?

 

Either way… surface temps of cylinders are a wild card…

The only reason we get useful info out of them is we use the exact location all the time…

Going to a different location…different number…

Adding JPI digital display… precise different number….  
 

Best regards,

-a-

[Buckeyechuck]

This is what I was looking for.  In type K .  

 

 

 

[carusoam]

33 minutes ago, Buckeyechuck said:

This is what I was looking for.  In type K .  

 

 

 

@Jeev have you seen the Ring thermocouple that fits under the bayonet’s holder?

Its a K-type thermocouple…

For some reason… the JPI website no longer shows this option…

Or it is hidden really well…

Best regards,

-a-

[carusoam]

Chuck,

Going to the EI website shows they have one…

https://www.iflyei.com/wp-content/uploads/P-102-38.pdf

Check with @oregon87 to make sure it is K-type and fits your application…

Oregon is an awesome MS support mechanism for Electronics International…

Best regards,

-a-

[oregon87]

I'll do my best to touch on a few things here.

1. In the states, type J probes utilize red and white wiring.  Type K utilizes red and yellow.  Super easy to determine which is which by checking the wiring.

2. Grounded probes typically to not work well where un-grounded probes are required.  All EI temperature probes are un-grounded.  An easy test to see what you currently have is to measure continuity from either of the probe's leads to the tip (or near) of the probe.  No continuity=un-grounded.  Continuity=grounded.

3. Measuring accuracy can be done is three simple steps.  One, before the engine is started, does the temperature match ambient, or close to?  Two, remove the probe and submerge it in an ice bath (70% ice/ 30% water).  The displayed temperature should be near 32°F.  Similar to the second test, submerge the probe in boiling water and look for a temperature near 212°F.  If all three known data points match, the probe is likely reporting accurate temperatures.

4. Different types of probes will report different temperatures as they are measuring the temp from different parts of the cylinder (well, under the well probe, upper spark plug and lower spark plug).  The well probe is the most common and the vast majority of published limits reference this location.  A piggyback probe under the well probe will report similar temperatures, but likely a few degrees less.  The upper spark plug CHT probe will report temps approx. 25-50°F cooler than the well probe due to engine baffling and the lower spark plug CHT probe will report temps approx. 25-50°F hotter than the well probe due to proximity to the exhaust.  

Hopefully that helps a bit.

Edited October 6, 2021 by oregon87

[carusoam]

23 hours ago, Buckeyechuck said:

This is what I was looking for.  In type K .  

 

 

 

For just the sensor, not including the threaded adapter…

The EI sensor, K-type… should be this one… at Spruce…

https://www.aircraftspruce.com/catalog/pnpages/10-02039.php?gclid=CjwKCAjwkvWKBhB4EiwA-GHjFvdHOFJtG3Zhr08R01ZqfUxhTP6GwAuuX5rJK8SYbDXg1zV-ZBOyIhoCugoQAvD_BwE

 

PP thoughts only, not a mechanic…

Best regards,

-a-

[Buckeyechuck]

On 10/5/2021 at 10:53 PM, carusoam said:

@Jeev have you seen the Ring thermocouple that fits under the bayonet’s holder?

Its a K-type thermocouple…

For some reason… the JPI website no longer shows this option…

Or it is hidden really well…

Best regards,

-a-

JPI site and Aircraft Spruce both have the ring. I have that version. Mine disagrees with factory gauge by 80 degrees. I’ve tested and they both agree in boiling water and at atmosphere. For some reason I’m not getting the heat transfer to the ring from the cylinder head. That’s why I’m looking for the bayonet holder version shown. Anyone have one out there they’re not using anymore. 

[carusoam]

One of these days…

Somebody is going to put two TCs on one bayonet to go in the one well that is available…

That guy is going to be a thousandaire!  Aka an AMU-anaire… 

 

See if @oregon87 knows why there isn’t a two TC option for the bayonet?

1) The experimental crowd doesn’t want it…

2) The certified crowd doesn’t want to pay for certification of a new type of TC…?

Certification of a new TC has got to be a low risk business endeavor…

The guy that makes this happen is going to look brilliant!

He could write that on his resume…

Best regards,

-a-