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What might cause low EGT?

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bifft

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Weather was great, so went for a flight today. About the time I got to pattern altitude I noticed that one EGT was really low. Like 800 compared to 1400 on the other. (I only have a dual EGT on cylinders 2&3 with CHT on 1&4, so don't have as much data as the fully instrumented folks). CHT was normal. Engine ran smoothly and seemed to be making full power (RPM and rate of climb were normal). Thought it might be a sign of an exhaust leak, so came back and landed. By the time I had the cowling off all of the exhaust tubes were cool to the touch, but cylinders were all still warm. Don't see any cracks, signs of exhaust leak.

Checking the video I took it was normal at startup, but then low by the run up. Run up was normal with no problems on either mag.

Planning on going back out tomorrow with my IR thermometer to check if it is just the sensor. Wanted to ask the people who actually know engines what else I should check. I don't know much beyond put gas in them and they go vroom.
 

Cass256

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I'm not an expert on engines or EGT probes, but to me this sounds like it could be a faulty sensor. The IR thermometer sounds like a good way to double check those, even if it's just a relative surface reading.
 

pictsidhe

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For the egt to be that far out, you'd have noticed the engine not running smoothly. Sensor is likely shorted close to exhaust. Try swapping them and see if the bad cylinder moves.
 

N804RV

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I had this problem once. EGT went low. But, the engine was running fine. Working on the assumption that if the exhaust gas temp was 'REALLY' that low, the engine would not be running normally, I went back to the hangar and went over everything from the egt probe to the back on the instrument. Didn't find anything I could point to and say, "That's it!" But, the problem went away and hasn't come back.
 

rbarnes

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Pull the spark plugs. If they're all the same color than I would start looking at the sensor and it's wiring.
 

TFF

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Diagnostic wise, I would do a compression check and if you have someone you trust, use your thermometer and check with one mag and then the other while running. I have had both be problems.
 

lakeracer69

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Wondering what engine it is? We have a fleet of flight school Rotax 912 powered RV's that seem to eat their EGT probes. Just saw another melted one yesterday. These guys are needing a 100 hour inspection once a month on average per airplane.

It's funny when I learned to fly in the early 80's we had no EGTs to worry about. You leaned it till it ran rough, and then backed it off till it ran smooth again. Flew many trouble free hours that way.
The young pilots and students who fly these RV's we work on think the worst when the EGT goes wonky or quits altogether with a red X on the EFIS. Sometimes too much information is just as bad as too little.
 

TFF

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With my old company helicopters, each would go through at least 2 every year. My friends Cirrus has always had connection problems. Changed connector types and probes. Always comes back.
 

bifft

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Utah
Thanks for the help.

It is on a O-360. Testing it today it does look like the sensor. Have ordered a new one, running the wires will be the only hard part.

I also never had a EGT before this airplane, put it in because everybody else does. Have tried to use it to lean, but it reacts too slowly. I just lean to max RPM and enrich a little (fixed pitch prop).
 

lakeracer69

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Also run a small zip tie or two (to get a proper length) between both wires on either side and around the connector to make sure it can't work itself apart. This is done all the time. You could also put some E4 on the connector pins before you assemble it.
 

TFF

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What kind is it? alumelcromel are slower reacting than just resistance type. That’s actually a good thing with fixed pitch. There is a dampening effect with them.
With resistance only , fixed pitch EGT will wander as the prop loads and unloads in the air. Drives some crazy. Constant speed holds the load so the numbers lock in a little easier.
 

bifft

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Apr 17, 2011
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Utah
Got the replacement in, installed it today. As expected took 5 minutes to replace the sensor and four hours to run the wires, put everything back together. Had a nice flight afterwards with good EGT readings the whole time. Supposed to be 2.5 ohms, the new one was, the old read 0 ohms.

Is amulemcromel, seems to take about 15 seconds to react, vs. instant with the rpm.
 
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