The International Cessna^® 170 Association

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

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

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.

GAHorn wrote: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

bgiesbrecht wrote: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

reecewallace wrote:

GAHorn wrote: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

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.