Cylinder head temps and thermocouples

[cbogie]

I read numerous posts in this forum about trouble controlling cylinder head temps.  That has never been my experience and I am beginning to wonder why my Bravo might be an outlier.  At 29/2400 and TIT of 1580-1610 I rarely see CHTs in the mid 300s at cruise. More commonly low 300s. Cowl flaps seem to work correctly and are in adjustment  

1. Do CHT probes get lazy like the TIT probe ?

2. any other ideas why my CHTs are lower?

3. What is an acceptable cooling rate when initiating a descent ? I usually back off 1 inch of Manifold pressure and initiate a 500 fpm descent which gives me a 10-20 degree per minute initial cooling rate 

thanks for the input.  
 

Charlie. 

[N201MKTurbo]

13 minutes ago, cbogie said:

1. Do CHT probes get lazy like the TIT probe ?

Thermocouples measure temperature at the junction where the two wires are connected together. The failure mode that will make them "lazy" is a breakdown in the insulation upstream from the intended junction. This allows the thermocouple wires to touch forming a junction at a cooler place then the end of the probe. The reading now becomes the average of the two junctions. 

[cbogie]

I understand.  But is it more likely that all 6 of my CHT probes have failed and are reading too low ( with about a 20 degree spread high to low ) , or that my CHTs really are in the 300s in cruise. ?  
I am going to put a few of them in boiling water this oil change. 

Edited July 26 by cbogie
Addition

[N201MKTurbo]

That is very unlikely, unless the pseudo cold junction in the instrument has gone haywire. 

A thermocouple makes a current between a hot junction and a cold junction. Most modern thermocouple instruments have a temperature sensor in the instrument to correct the thermocouple reading for the cold junction. this makes a pseudo cold junction. if that temperature sensor isn't reading right, it could affect all of the readings. It would most likely affect all the readings not just the CHT readings. the best way to check is to look at the readings with the engine stone cold. all your thermocouples should be reading OAT.

https://www.omega.com/en-us/resources/thermocouple-junction-principles#

https://www.allaboutcircuits.com/technical-articles/what-is-cold-junction-compensation-in-thermocouple/

[LANCECASPER]

13 hours ago, cbogie said:

I read numerous posts in this forum about trouble controlling cylinder head temps.  That has never been my experience and I am beginning to wonder why my Bravo might be an outlier.  At 29/2400 and TIT of 1580-1610 I rarely see CHTs in the mid 300s at cruise. More commonly low 300s. Cowl flaps seem to work correctly and are in adjustment  

1. Do CHT probes get lazy like the TIT probe ?

2. any other ideas why my CHTs are lower?

3. What is an acceptable cooling rate when initiating a descent ? I usually back off 1 inch of Manifold pressure and initiate a 500 fpm descent which gives me a 10-20 degree per minute initial cooling rate 

thanks for the input.  
 

Charlie. 

I've had three Bravos and have never seen low 300's in cruise. If those numbers are correct you likely have the coolest cylinders of any Bravo on the planet or you are flying in the Arctic Circle. . . lol.  Since you have a 1995 Bravo and you have a CHT reading on each cylinder you're using an aftermarket engine monitor - which one are you using?

[Fritz1]

Flew the Bravo from Pierre SD to Bozeman MT today at FL200, TIT 1580, hottest CHT 385, OAT -10C, 29" 2400 FF 21Gph, TAS 188KT, for my Bravo this is about normal, from all I have read this is pretty good for a TKS Bravo, as you said check all probes in boiling water, they are reading low, what does your probe on the Moritz read if you still have one? , call JPI and see what they come up with