Hoeschen Posted December 12, 2016 Report Share Posted December 12, 2016 M20C standard 6 pack engine gauge cluster. When I turn on the master my CHT needle pegs to the right. I have an EDM that I also use but would like to get it fixed. Do you think this is the gauge or the probe? The oil temp gauge is also erratic until it gets warmed up. Do these gauges need replacement or is this the probes going bad? Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
carusoam Posted December 12, 2016 Report Share Posted December 12, 2016 That group of gauges often has grounding issues that can give some challenges. Have you disconnected the plug parts associated with it? Have a can of electronics cleaner? The CHT is a simple voltage source provided by a single thermocouple mounted on one cylinder. The normal voltage range is in micro volts. so a transient source of voltage difference can really swing the needle. Fortunately, you don't even have to run the engine to look for the problem... See if all the grounding straps are actually working properly. This way stray voltage isn't running from the engine to the panel via the TC. More PP ideas, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
DonMuncy Posted December 12, 2016 Report Share Posted December 12, 2016 40 minutes ago, carusoam said: The CHT is a simple voltage source provided by a single thermocouple mounted on one cylinder. The normal voltage range is in micro volts. so a transient source of voltage difference can really swing the needle. On my K model, the factory gauge is hooked to a thermistor (sp?). It is a variable resistor that varies with temperature. One wire to the gauge is hot and the other one goes to the thermistor on the cylinder. So if the gauge pegs, it indicates the wire going to the cylinder is grounded. Ie, either a short or a bad thermistor. Quote Link to comment Share on other sites More sharing options...
carusoam Posted December 12, 2016 Report Share Posted December 12, 2016 Hmmm... Don, are you sure your CHT is a thermistor? The OilT is definitely a thermistor. In the industrial world thermistors have been leaving in droves. Not sure why we are still using them in aviation. Of course our CHTs are nicely jacketed so they look more bulbous like a TC. They were great for their accuracy in tough environments. The TC requires sensitive electronics to pick up a tenth of a degree in the equivalents of milivolts. Where would I look up the CHT sensor for the K...? Best regards, -a- Quote Link to comment Share on other sites More sharing options...
DonMuncy Posted December 12, 2016 Report Share Posted December 12, 2016 I won't bet my life on anything, but I'm pretty sure it is. Quote Link to comment Share on other sites More sharing options...
carusoam Posted December 12, 2016 Report Share Posted December 12, 2016 I found a manual for the Continental IO520... It is an interesting read. 100 pages. Direct info by the engine manufacturer, that may not make it into the airplane's POH... http://www.tcmlink.com/pdf2/MaintenanceManuals/X30041/X30041.pdf Under instrumentation it lists.... "Indicates temperature measured by Bayonet Thermocouple, Aeronautical Standard AS234 Element or equivalent. installed in boss in bottom of cylinder head. " They don't give any detail of J or K type thermocouple. Max CHT is a whopping 460° F. Of course, you would want something directly related to your TSIO360 for better reference. Under the section related to abnormal operations, they describe oil T problems and say check the thermocouple...(?) I think the thermistor might run into some difficulty with the Temperature range of the CHT. Whatever they have in there can't be too sensitive to temperature. I could not find the date, but it was not a real electronic copy... the first page had a 2011 date. But the second page through the end was not from the same source... This is from a PP reading technical data, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted December 12, 2016 Report Share Posted December 12, 2016 I would check the connectors and wires. Quote Link to comment Share on other sites More sharing options...
Hank Posted December 12, 2016 Report Share Posted December 12, 2016 3 hours ago, Hoeschen said: M20C standard 6 pack engine gauge cluster. When I turn on the master my CHT needle pegs to the right. I have an EDM that I also use but would like to get it fixed. Do you think this is the gauge or the probe? The oil temp gauge is also erratic until it gets warmed up. Do these gauges need replacement or is this the probes going bad? Sent from my iPhone using Tapatalk That happened to me once with the Oil Temp. The safety wire for my oil filter wraps around the base of the oil temp probe, and it had slipped off and touched the top of it above the gasket. Master on, needle pegged. Have you had (or done yourself) any work under the cowl recently? I'd bet on something similar and as easily corrected before the probe going bad. Most thermocouples anymore fail to "0" rather than "999", too, although there are still some of the old ones out there. Quote Link to comment Share on other sites More sharing options...
Danb Posted December 12, 2016 Report Share Posted December 12, 2016 Try cleaning the contacts. I had similar issues, cleaned and sprayed contacts all better. Quote Link to comment Share on other sites More sharing options...
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