Barit:
Well, this may or may not be true for a given engine type [that ITT rises in the climb due to reduced mass flow rate of air], depending on the characteristics of the control system (whether governing to a constant core speed, constant corrected speed, constant torque, constant CDP, etc etc.)
No doubt you're quite right. However, I was responding to aerobat's specific scenario regarding his specific type in which he
observes an ITT rise.
If you follow the thread back you will find this comment by aerobat which gives context:
i think slippery pete is pretty right with the higher compression- lower exhaust temperatures at pistons . you can see this effect also in tubine engines where maintaining the same power output / fuel flow in a climb will result in exhaust temperature RISING due to thinner air and worsening compression of the compressor stages
My point is that if you observe such a rise in those circumstances there is a good alternative explanation; namely less cooling air available.