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CHT / EGT

WillG

Member
With a O320 Carbed Engine

With CHT for ea. Cylinder
Do I really need a EGT for more than one Cylinder.
Of so why.

Thanks


Will
 
EGT gives you a measure of the fuel air mixture in each cylinder. With a carbureted engine mixture distribution between cylinders is uneven enough that using EGT as a leaning reference only gets you so far. However, it is a great diagnostic tool for ignition, intake, and exhaust issues.

If you have a plug go bad you can use the all cylinder EGT to figure out exactly which one before you even decowl. You can also use anomalies in EGT on one cylinder compared to the rest and combined with CHT info to detect valve problems or intake leaks.
 
CHT/EGT

Thanks Dan-

I was thinking the EGT would follow the CHT with an issue.
In other words, assume the gauge and probes are good, can you
have a low EGT with a good consistent CHT numbers on all Cylinders

Thanks

Will
 
EGT as a diagnostic tool

A few years ago flying home from visiting my parents, I noticed while in cruise flight that EGT on cylinder #3 started creeping up far out of its normal range (carb engine). The engine kept humming along without missing a beat.

Knowing that this likely meant an ignition problem in cylinder #3, an in-flight mag check was performed. Sure enough, when the left mag was turned off, the engine was clearly only firing on 3 of the 4 cylinders. Back on both mags, I made a precautionary landing at the nearest airport.

Because I carry a small tool kit with me that includes a spark plug socket, I was able to immediately follow the RH mag to cylinder #3, and found it was the top plug. I knew exactly which plug to pull within seconds of de-cowling.

Sure enough, the top plug had a lead ball shorting it out, which was quickly cleaned. Re-installed, test run, re-cowled, and back on my way home in less than 30 minutes from landing.

This is one illustration of the benefits of full EGT monitoring. Had I only monitored EGT on Cylinder 3, that could have led me down a much more tedious diagnostic path. Had I only monitored EGT on a single, but different cylinder, I would have flown on without knowing there was an issue until my next mag check prior to going somewhere. Again, diagnostics would be a bit tougher - perhaps suspecting a mag problem or pulling more plugs than necessary to find which cylinder was the culprit. CHT never changed, or at least not enough to notice. The cylinder was still producing plenty of power while it ran happily along with one spark plug firing.
 
Here is another example. I was having issues with rough running left mag during in flight mag check.

Note in the table below, the CHT when running on the left mag showed a -5F drop in CHT for cyl 2 and 6. However, note that the EGT for #2 dropped -58F but #6 when up +86F.

TJ
 

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I agree with everything that's been said already. I can't tell you how many hours of labor were saved in our old shop because we installed EGT probes on every cylinder. (I used to work for an LSA manufacturer). Intake leaks, spark plug & plug wire issues, carburetor adjustment, valve issues-- basically any time an engine felt off or ran a little rough, a high or low EGT was the first clue. Things would sometimes show up on the EGT indication before you even felt any roughness. EGT indication is instantaneous, whereas CHT is dampened out because of the mass of the cylinder head. Sure, if you have a dead cylinder it will eventually show up as a cooler CHT, but not as clearly or quickly as EGT. Definitely recommend it!
 
All good information, makes sense to have both both on all cylinders.

Thanks for the input guys.


Will
 
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