Thought I would stir the pot??
https://www.savvyanalysis.com/articles/egt-myths-debunked

Why would you think that posting this would be pot stirring? Knowing what EGT is and isn't is one of the steps to becoming an educated pilot. It probably doesn't matter to those who fly with single probe instruments. But it is common knowledge for those who fly injected engines LOP with multi-probe engine analyzers. No pot stirring in that link....just plain Jane education. I took the Advanced Pilot Seminars online course 4 years ago and am a believer in the benefits of LOP operations. I think my savings to date exceed $10,000. Wow, that was some serious thread drift. Sorry Zane.

I think it depends on what you're trying to achieve and how your plane is equipped. There is a great article out there about relative vs absolute EGT and why the former is the one we care about.

My plane didn't have one when I got it, I put a single probe in and feel having at least some idea of my temp no matter how basic is much better than no idea at all.

I agree with much of the article, but the author seems to negate the possibility of burning a valve, either by running to too hot, or by running too cool and allowing lead to build up and interfere with the heat transfer when the valve closes. CHT's aside, you can cause problems with too high/low EGT's. You can't control what you can't measure.

And if you know your engine well enough, absolute numbers DO have meaning. I know what temperature to run my EGT's in cruise so my spark plugs all come out a nice light brown with minimal leading and no scorching. It took several years and lots of spark plug cleanings to compile that information, but it is relevant. A numberless graph would do the same thing, but my engine monitor has numbers, so I learned to use them.

The multi-probe EGT also lets me select the throttle setting which will allow me to lean without any cylinder getting too hot or too cold...no burning, no lead build up. There's a very specific spot on the throttle that allows that, and any other throttle setting will produce very large EGT spreads. The author states there's no benefit to equalizing EGT's, but I don't agree with that. If you can run all your EGT's at the same temperature, you can lean so as to prevent lead buildup or overheated valves in any cylinder. Granted, you could accomplish the same thing without using absolute numbers, but the point is running all the cylinders at the same EGT has advantages.

My engine cowl is a huge PITA to remove and replace. It's a 60 minute job. So not having to pull spark plugs because they're leaded up is rather important to me. And the lead buildup from running cylinders too cool can be more damaging to valves than running them too hot. The valves' primary cooling mechanism is the heat transfer to the valve seat when it closes. If that connection between the valve and valve seat is interrupted by lead build up, then the valve dissipates heat poorly and unevenly, so that at even low EGT's the valve can overheat and be damaged.

So while I agree that the actual numerical EGT readout is meaningless as stand-alone information, I don't at all agree with the implication that if you mind your CHT's you can ignore your EGT's.

I've not come up with a good technique for balancing my EGTs. I'll fiddle with the mixture and throttle until I get the combination that gives me fuel flow I want with relatively balanced EGTs. I'd be interested in hearing your technique. Thanks!


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Well, I don't really have a technique. I just found that a fingers-width back from full throttle gives me the most balanced fuel flow and level EGT's. It's essentially full throttle but without opening the enrichment needle.

If I crack the enrichment needle open, all hell breaks loose from a temperature standpoint. Some EGT's go cold and others super-heat.

Side note, if I'm going to lean for high-altitude take off, I don't firewall the throttle, but rather advance to that sweet spot before the enrichment needle opens. I can feel where it is by putting one finger between the throttle knob and the panel.

Leaning for take off and going to full throttle will put one of my EGT's into the 1,800 degree area before the others even reach 1,200 degrees, and my cruise limit is 1,320 degrees. After that the plugs go white, which is too hot. Does operating for a couple minutes at 1,800+ degrees damage my engine? I don't know, but it doesn't seem like it's very good for it.

If I go to full throttle and keep my hottest EGT within limits I get less power than if I keep the enrichment needle closed and lean more aggressively. All things I never would have known without a engine analyzer.

That anyone will own a $40,000 internal combustion engine, with no inherent safety mechanisms, which their very life depends on, and then not spend a couple thousand dollars on instrumentation to monitor how it's running is just baffling to me.

Thanks for the info. I always find it interesting to hear how people run their engines when they have them dialed in. I felt like I had my IO-470 dialed in, but I'm still in the experimental stage with the IO-520 I now have. I've got less than 50 hours with it and the majority of the flights have been short. I'll keep tinkering with it to learn its quirks.

I totally agree about the engine analyzer. It's a must have in my opinion.


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Good article.... Just installed the CGR30P. The EGT on all four is an added benefit. When I think about EGT temperature readings, the picture or video in my mind is of running a gas pot engine without exhaust manifolds. The flame front from each port looks fairly even but isn't. Then consider the variance in aircraft exhaust manifolds, the distance and orientation of the pyrometer probe is not precise or concentric which can create a wide variance in the EGT temperatures. About the only applications I know of that require precise monitoring of EGT temperatures, at a predetermined temperature by the engine manufacturer, are USN diesel propulsion systems.


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I agree with Hammer. You don't know what you don't see. High CHT issues, too lean a cylinder, timing issues, and many other problems have most surely see you but with out proper instruments you never saw them!!!!! Lots of engines run to TBO if you keep replacing cylinders. Instruments can save days of guess work/ $$$$, when trying to find a problem, and will tell you early on before a problem becomes a emergency. Old school way of thinking was you could tell hot things where by the oil temp. If you have a properly instrumented engine you will quickly understand this is false. EGT is a useful tool if you know how to use it. It is even better if you add CHT, fuel flow, and MAP. Carb/ injected, fixed pitch, or constant speed prop. Gauges will help if you learn how to use them.
DENNY

I normally don't give my EGTs too much attention and focus mainly on CHT, but seeing one really high EGT helped me diagnose an ignition problem the other day (1 lead went bad) when a pre takeoff mag check showed no issues. It was running ok on both mags and I might not have noticed other than the high EGT. Started flipping the mags off one at a time and watching EGTs to isolate the problem to the one cylinder on the one mag. Swapped plugs top to bottom and isolated the lead. Took about 20 minutes of work to diagnose because my EGT/CHT are instrumented and I try to stay familiar with the ballpark of numbers I normally see at different power ranges.

After running my Lycoming 360 for the last 3 1/2 years with an Insight G1 analyzer, I've watched the EGTs but I haven't seen anything abnormal, and I don't have to fly it any different. The highest I've seen is about 1600 degrees, more typically in the high 1300s. Mostly I'm more concerned with CHTs, because the back 2 cylinders run hot and can easily overheat if I'm not careful. I've tried various things to get the EGTs to run at similar temps, but the only thing which has worked so far is at cruise (typically 2400 rpm and 21" or whatever MP I can get at higher altitudes), if I pull on partial carb heat for a few moments, they'll even out, and then when I push it back in, they stay pretty even for awhile.

Cary

I have thousands of hours in C-152 and C-172 with stock Lycoming engines and no EGT and hundreds of hours cleaning plugs. Engine life was not a problem; we got 1800 on 152s and 3000 hours on 172s between overhauls. Lead fouling of lower plugs was a big problem, especially on the 152s that were supposed to like 100LL. Never made the 100hr (monthly) on any 152 without having to clean bottom plugs at 50 hrs. Lots of lead every 50 hours. If Hammer has and EGT technique to mitigate that problem, pipeliners would want to know. Whether they can get Uncle Rick to install EGTs is another question.

100LL has enough lead for big engines. I wonder if EGT would help with the smaller engines that don't like all that lead? I assumed they didn't run hot enough, but I'm not a mechanic. We leaned all small Lycoming engines to max RPM before takeoff, regardless of density altitude.

Squash wrote:Why would you think that posting this would be pot stirring? Knowing what EGT is and isn't is one of the steps to becoming an educated pilot. It probably doesn't matter to those who fly with single probe instruments. But it is common knowledge for those who fly injected engines LOP with multi-probe engine analyzers. No pot stirring in that link....just plain Jane education. I took the Advanced Pilot Seminars online course 4 years ago and am a believer in the benefits of LOP operations. I think my savings to date exceed $10,000. Wow, that was some serious thread drift. Sorry Zane.

I couldn't agree more. +1!

Hammer wrote:And the lead buildup from running cylinders too cool can be more damaging to valves than running them too hot. The valves' primary cooling mechanism is the heat transfer to the valve seat when it closes. If that connection between the valve and valve seat is interrupted by lead build up, then the valve dissipates heat poorly and unevenly, so that at even low EGT's the valve can overheat and be damaged.

....
The multi-probe EGT also lets me select the throttle setting which will allow me to lean without any cylinder getting too hot or too cold...no burning, no lead build up. There's a very specific spot on the throttle that allows that, and any other throttle setting will produce very large EGT spreads. The author states there's no benefit to equalizing EGT's, but I don't agree with that. If you can run all your EGT's at the same temperature, you can lean so as to prevent lead buildup or overheated valves in any cylinder. Granted, you could accomplish the same thing without using absolute numbers, but the point is running all the cylinders at the same EGT has advantages.

I agree - but surely the lead scavenging agents in the fuel and their ability to function properly is best measured by CHT as a proxy for combustion temperature, rather than "gauge" EGT which the article focuses on? Noting that gauge EGT and combustion temperature bear a loose relationship to one-another, whereas CHT bears a more direct relationship. But I am generalising, which is always risky.

I don't agree about balancing EGTs, that's also a function of where the probe is placed and the airflow out of each cylinder. To me, it's not a good gauge of what's happening inside the cylinder in absolute terms - it's only useful in a relative sense. Because of that, having all the EGTs reading the same number doesn't mean anything, I subscribe to the peak EGT spread vs fuel flow rate school of thinking.

I also have been a big fan of multiprobe EGT gauges for many years. I met and talked with George Braley at length some 15 years ago about running LOP and the need for multiprobe EGT gauge.
I belong to the same school of thought about knowing peak and fuel flow variations is far more important than trying to balance EGT's.
Back in my 180 days I was told the way to run the throttle, when high enough, was to back off from full to the point where you just saw the MP gauge start to decrease then in a bit. The theory was that this cocked the butterfly in the carb just enough to create enough turbulence to help the fuel atomize better.

Tom

a3holerman wrote:Back in my 180 days I was told the way to run the throttle, when high enough, was to back off from full to the point where you just saw the MP gauge start to decrease then in a bit. The theory was that this cocked the butterfly in the carb just enough to create enough turbulence to help the fuel atomize better.

Tom

When I was running my IO-470, I had my Gami spread down to a 0.2 but it still wasn't running smoothly past 40 degrees lop. I talked to Gami and they said to bring the throttle back 1/4 to 1/2" manifold pressure. He told me they weren't sure exactly why that trick works (injected vs carbed) but that it works. (Or more likely he knows and just didn't have time to explain it. Can't imagine them not knowing.) Anayway, sure enough. Brought the throttle back and it ran nice and smooth up to 60 degrees lop. Anyone know what that does on an injected engine?


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Interesting,
I also had a IO-470K in a Debonair that did not run well LOP but I did save over 1.2GPH running 100 ROP. over the stock injectors.
Talked with Braly about that too an he thought it might have something to do with the lower compression "K" model.