How does exhaust heat affect CHT probe wires?

[John Richardson]

My JPI EDM-800 installation guide says not to route the probe wires near hot areas, such as an exhaust stack. Of course, this is almost impossible given that we are probing a hot engine, after all.

What affect does heat have on the probe lead? Will it cause incorrect readings? Will it melt? How sensitive is it? Can it be routed NEAR an exhaust pipe so long as it doesn't touch it?

I can't seem to find any information on this...

 

[Pilot Steve]

I've never had an issue with the CHT wires. But I do go through EGT probes that burn off.

 

[Tarheelpilot]

I always tried to run them up and aft. The wires getting hot will not affect reading to my knowledge. If they get too hot they melt and cease to function.

 

[Stewartb]

The probe is a thermocouple. The wire just carries the signal the thermocouple sends. I think.

 

[3393RP]

The probe is a thermocouple. The wire just carries the signal the thermocouple sends. I think.

That's correct. A thermocouple consists of two dissimilar metals that form an eletrical junction, and when subjected to heat, produce a measureable voltage signal.

Thermocouples are inexpensive and reliable. While the wire and insulation is designed to have resistance to high temperatures because the installation is obviously exposed to a hostile environment, they're still subject to damage if thermal limits are exceeded.

 

[Chip Sylverne]

The wire itself is chromel / alumel an alloy of chrome and nickel. You can't just use good ol' copper if you need to replace some thermocouple leads.

 

[John Richardson]

If the lead is in direct contact with a 1300F exhaust pipe, could it affect the readings on the display?

 

[Bell206]

If the lead is in direct contact with a 1300F exhaust pipe, could it affect the readings on the display?

FWIW: It shouldn't but depending on the t-couple insulation, etc. it could induce an error. Best to isolate the t-couple cable using appropriate adels or other stand-off items.