Erratic EGT
03-23-2013, 08:42 PM
#1
On Reserve
Thread Starter
Joined APC: Jan 2009
Position: Shorts 330
Posts: 18
Erratic EGT
Hello all,
The family truckster 182 came out of annual and on the first flight about 15 min in the EGT on #2 cylinder flashed a spike then dropped back to "normal" a few min. later it did it again. We turned back for home and watched it. No rise in CGT or roughness. After landing we ran it up on the ground. Spike not repeated. At annual we changed out old tie wraps for Adel clamps and moved some wires around. We thought the spike in egt could be a bad sensor wire but were unable to get it to repeat on the ground.
So has anyone had a single cylinder EGT spike that was not constant and what was the culprit.
My dad's most of the way through A&P school so this is mostly a thought exercise until the shop opens on Monday.
Thanks
The family truckster 182 came out of annual and on the first flight about 15 min in the EGT on #2 cylinder flashed a spike then dropped back to "normal" a few min. later it did it again. We turned back for home and watched it. No rise in CGT or roughness. After landing we ran it up on the ground. Spike not repeated. At annual we changed out old tie wraps for Adel clamps and moved some wires around. We thought the spike in egt could be a bad sensor wire but were unable to get it to repeat on the ground.
So has anyone had a single cylinder EGT spike that was not constant and what was the culprit.
My dad's most of the way through A&P school so this is mostly a thought exercise until the shop opens on Monday.
Thanks
03-23-2013, 10:10 PM
#2
Disinterested Third Party
Joined APC: Jun 2012
Posts: 6,103
Not enough information is given, but with your recent return from annual and the change in fasters, chances are that you have a ground issue which is intermittent.
EGT fluctuations can be actual changes in exhuast gas temperature, but if you're using an analog gauge and a standard thermocouple, the changes don't register that quickly.
You may have a bad thermocouple, though they don't tend to cause erratic variations. Bad thermocouples tend to read incorrectly, and are typically off by a constant value.
You may have a bad instrument. That does happen.
Most likely, however, you have a ground issue, probably with pinched wiring or a spot where the thermocouple lead has worn through against the engine mount, or though a firewall. As the wiring has recently been moved, this is the most likely possibility.
EGT fluctuations can be actual changes in exhuast gas temperature, but if you're using an analog gauge and a standard thermocouple, the changes don't register that quickly.
You may have a bad thermocouple, though they don't tend to cause erratic variations. Bad thermocouples tend to read incorrectly, and are typically off by a constant value.
You may have a bad instrument. That does happen.
Most likely, however, you have a ground issue, probably with pinched wiring or a spot where the thermocouple lead has worn through against the engine mount, or though a firewall. As the wiring has recently been moved, this is the most likely possibility.
03-24-2013, 06:33 PM
#3
ATC retired/121 hired
Joined APC: Dec 2012
Position: 121 FO / glider for fun
Posts: 164
Is it possible you had something cause a stuck exhaust valve? Carbon, dirt or something else that got into the cylinder while the plugs were out, and caused a temporary blockage then burned off? Cessna pilot's association is a great source for these type of questions. I was a member when I had a C172 and the membership was worth every penny.
