Broken CHT - Replacement?

[reecewallace]

My CHT gauge stopped working in flight today, and I'm looking for a replacement/repair. My AME and I took the system apart, but couldn't see any broken wires or obvious signs.

I'm not sure if it's the gauge, wires, or probe—impossible to know without replacing each piece independently.

I figure it's best to replace the entire system if it's not too expensive.

Anyone know where I can get a replacement gauge, probe, and wires to match my current one? Or is there a similar slide in replacement for my panel? Current P/N is 29-2006

Mine only reads 1 cylinder, which I'm fine with

[GAHorn]

The gauge can be tested. The probe is the most common failure after harness integrity has been confirmed.

[bgiesbrecht]

Agreed, in my experience it is common for the gasket-style probe to fail especially after working on the plugs. I would start with simply replacing the gasket probe after checking the harness connections.

[reecewallace]

The gauge can be tested. The probe is the most common failure after harness integrity has been confirmed.

Two questions—

1. How do I test the gauge?
2. P/N for new probe?

I inspected the harness. It's old, but looks OK

[reecewallace]

Agreed, in my experience it is common for the gasket-style probe to fail especially after working on the plugs. I would start with simply replacing the gasket probe after checking the harness connections.

Thanks for this. You can see my Q's to GAhorn above

[GAHorn]

The gauge can be tested. The probe is the most common failure after harness integrity has been confirmed.

Two questions—

1. How do I test the gauge?
2. P/N for new probe?

I inspected the harness. It's old, but looks OK

Aircraft Inst and Development has a phone number: 316 775-1144

If you remove the probe…. you can use an ohm meter to test for continuity…then heat the probe with a hair dryer and see if the resistance changes to indicate a working sensor.

J-type CHT probes (gasket style) are available from instrument repair shops and from aircraft suppliers such as Aircraft Spruce: https://www.aircraftspruce.com/search/search.php

[DaveF]

Reece,

I’m guessing that the gauge uses a thermocouple sensor, as George suggested. Is the sensor a gasket that fits under the spark plug? Are the sensor wires color-coded? If red-white, it’s a J-type thermocouple. If red-yellow, it’s K-type. The only thing that can go wrong with a thermocouple is that wires break and it goes open-circuit. Disconnect it from the gauge and measure the probe resistance. If it’s a few tenths of an ohm then it’s probably ok. To test the gauge you should find another probe of the same thermocouple type and see what it does.