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Importance of single EGT...

ccsmith51

Well Known Member
I have a Westach dual CHT/EGT gauge. On my last couple of flights the EGT has acted sporadically. It is in the right exhaust below the connection of the two pipes. The engine runs fine. Basic troubleshooting indicates it is either a probe or a connection.

I plan on replacing the complete unit with new probes. Mainly because when I checked the instrument with boiling water the CHT read about 20? low. It has the plug ring sensor and from what I understand the bayonet sensor is more accurate, so I am changing to that.

But I was wondering about the real value of a single point EGT....

I follow the 48 rule of thumb, where about 75% power is when the combination of RPM and MP equals 48. If I am at 48 or above, I don't lean. If below, then I lean. Since I don't attempt to run LOP on a carbureted engine my leaning procedure is Lycoming standard: lean to onset of rough running, then richen to smooth.

In this case, what valuable information does the EGT provide?
 
But I was wondering about the real value of a single point EGT....

I follow the 48 rule of thumb, where about 75% power is when the combination of RPM and MP equals 48. If I am at 48 or above, I don't lean. If below, then I lean. Since I don't attempt to run LOP on a carbureted engine my leaning procedure is Lycoming standard: lean to onset of rough running, then richen to smooth.

In this case, what valuable information does the EGT provide?

I have one EGT probe on #3, been that way since the RV-6 (carburetor) first flew in 1999.

I've been through the same thought process and can't really see much value in the single EGT probe. Temp goes up as I lean but since it is only one cylinder the number isn't worth much. There are thousands of light singles out there without an EGT gauge and they've managed to survive somehow. :)

If the EGT probe croaked I probably wouldn't replace it until a more complex monitor replaces my uMonitor.
 
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Every since I was disabused from using the EGT in the leaning process, the only time I use it now is on runup to check that all four EGTs go up when I shut off a mag and then the EI. The value of knowing which cylinder is problematic at that point is clear to me.
 
My RV-6 also has a single EGT/CHT, on the #4 cylinder. I don't use it to lean other than as a crosscheck and a reference for consistancy. I agree with Sam in that in the event of failure I probably wouldn't spend any money on fixing it. At some point I will be adding a full complement of sensors and engine monitoring, I would likely have to do without it until then.
 
I am considering no EGTs on my UL 260is. As this is a FADEC engine with no manual A/F adjustment, would I be giving up in anything terms of engine diagnosis?
I am planning 4 CHT sensors.
 
Larry, I am not an engine guy, but I think you would. If you had four EGT's then you could monitor each cylinder. If one got out of whack relative to the others then you would know which one. If you had a spark issue you would know which one. It seems to me that there is a lot of operational and diagnostic information you could get by having four EGT's as well as four CHT's.
 
Started with 1 probe EGT now have 4

It is not essential for flight but if you are trying to extract maximum performance it is pretty essential. When Jeanine and I built the plane I put a probe in the cylinder 4 exhaust only - like our Archer II. I race the plane so I wanted to get the right mixture for maximum performance so I installed a 4 probe EI system. It worked great. I had to select what cylinder I wanted to look at one at a time but I could find the peak cylinder and lean based on the old first sign of "roughness" procedure based on the peaking cylinder. Red Hamilton modified the engine for me by adding high compression pistons, physically balancing all of the components and sending the cylinders to Barrett's in Tulsa for flow balancing. To my surprise after decades using the roughness back-off leaning technique I now have an engine that does not get rough as I lean. I must visually determine which cylinder is peaking, recognize that peak when it happens and back off from the peak on the correct cylinder. I installed a EI bar graph and digital combination EGT & CHT gauge which has a lean function separate from the normal gauge function that shows the peak and what cylinder it is. At the same time I bought and installed a EI fuel flow gauge with a HP function. The HP function is meaningless for my purposes unless the the max power zone is first found with the EGT leaning procedure. When that is done the power can be fine tuned through a very narrow node of maximum power using the mixture and the Horse Power function of the fuel flow gauge. I am still working with this but I was surprised by the narrow mixture range of the maximum power node.

Bob Axsom
 
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Most all of my flying was in higher altitude mountain country. I learned early on, which "lean" settings worked best for my carbed Lycoming. That single #3 EGT was one of the best instruments I had, for letting me know if the mixture knob was in the ballpark......or if it was time for an adjustment. I didn't use it as a direct method of leaning.

I'd have prefered gauges for all cylinders. But as a single one, it was very valuable.
 
Keep in mind I am unable to adjust mixture. The ECMs (dual) does that using throttle position, oil temp, crank position and MAP. I am wanting to know if there is any engine diagnosis I would be unable to benefit from without the EGTs.
 
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