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
Broken CHT - Replacement?
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
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reecewallace
- Posts: 165
- Joined: Tue Jan 05, 2021 1:34 am
Re: Broken CHT - Replacement?
The gauge can be tested. The probe is the most common failure after harness integrity has been confirmed.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
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bgiesbrecht
- Posts: 95
- Joined: Wed Feb 13, 2019 10:51 pm
Re: Broken CHT - Replacement?
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.
Former owner of:
1953 170B
N1977C
s/n 26122
1953 170B
N1977C
s/n 26122
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reecewallace
- Posts: 165
- Joined: Tue Jan 05, 2021 1:34 am
Re: Broken CHT - Replacement?
Two questions—GAHorn wrote:The gauge can be tested. The probe is the most common failure after harness integrity has been confirmed.
1. How do I test the gauge?
2. P/N for new probe?
I inspected the harness. It's old, but looks OK
- Reece
1956 Cessna 170b
Nanaimo, BC Canada
1956 Cessna 170b
Nanaimo, BC Canada
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reecewallace
- Posts: 165
- Joined: Tue Jan 05, 2021 1:34 am
Re: Broken CHT - Replacement?
Thanks for this. You can see my Q's to GAhorn abovebgiesbrecht 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.
- Reece
1956 Cessna 170b
Nanaimo, BC Canada
1956 Cessna 170b
Nanaimo, BC Canada
Re: Broken CHT - Replacement?
Aircraft Inst and Development has a phone number: 316 775-1144reecewallace wrote:Two questions—GAHorn wrote:The gauge can be tested. The probe is the most common failure after harness integrity has been confirmed.
1. How do I test the gauge?
2. P/N for new probe?
I inspected the harness. It's old, but looks OK
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
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
Re: Broken CHT - Replacement?
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.
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.