EGT - How hot is too hot?

[ilovecornfields]

I’ve noticed that at the power settings that I usually use on my Ovation (18”/2300 RPM) if I lean to 10.5 - 11 GPH the EGT approaches redline. I usually try to run 100 degrees below redline (either ROP or LOP) but I was wondering if I need to run cooler. If I run much leaner the engine doesn’t feel as smooth. I can run richer but I guess I’m not sure how much richer I need to go.

The engine has been running great. Compressions, valves, plugs, oil analysis all look good. 

[Niko182]

58 minutes ago, ilovecornfields said:

I’ve noticed that at the power settings that I usually use on my Ovation (18”/2300 RPM) if I lean to 10.5 - 11 GPH the EGT approaches redline. I usually try to run 100 degrees below redline (either ROP or LOP) but I was wondering if I need to run cooler. If I run much leaner the engine doesn’t feel as smooth. I can run richer but I guess I’m not sure how much richer I need to go.

The engine has been running great. Compressions, valves, plugs, oil analysis all look good. 

At that power setting you can run at any point, lean, rich, or at peak and not hurt the engine. There isn’t a limit on EGT. It’s just a baseline where you are in relationship to peak. On turbo charged airplanes you usually need to run 50 to 100 lop in order to not break the max TIT. But on NA engines most people run 20 to 10 degrees LOP. That is below 70% power.

[ilovecornfields]

I guess that was my question. Is there any harm if I run at “redline” EGT if the CHTs are good? Am I going to melt the exhaust and have it fall off the plane?

[Niko182]

In my experience no. My exhaust and engine both made it to 2200 hours before I finally replaced them. The most of the time I just went 10 to 20 LOP and that did the trick for me. I would guess @StevenL757 Probably would have more experience along that topic, but I thought I'd through my experience in there as well. He's had his ovation quite a bit longer than me.

[PT20J]

Where did the redline come from? I don’t see a limitation in the M20R POH. You cannot really get the EGT hot enough to damage anything on a normally aspirated engine. 

[Niko182]

Just now, PT20J said:

Where did the redline come from? I don’t see a limitation in the M20R POH. You cannot really get the EGT hot enough to damage anything on a normally aspirated engine. 

Pretty sure his plane still has the mauritz gauges that have a redline on them. If it’s the plane I’m thinking of he has a JPI and mauritz gauges with a limit on them.

[ilovecornfields]

28 minutes ago, Niko182 said:

Pretty sure his plane still has the mauritz gauges that have a redline on them. If it’s the plane I’m thinking of he has a JPI and mauritz gauges with a limit on them.

You are correct, sir.

[FlyingScot]

2 hours ago, Niko182 said:

Pretty sure his plane still has the mauritz gauges that have a redline on them. If it’s the plane I’m thinking of he has a JPI and mauritz gauges with a limit on them.

FYI - 

[ilovecornfields]

[Echo]

1 hour ago, ilovecornfields said:

that's a beautiful panel

[0TreeLemur]

I've never seen EGT as high at 1650F in a non-turbocharged engine.   The highest I've ever seen is maybe 1500-1550.

[A64Pilot]

25 minutes ago, 0TreeLemur said:

I've never seen EGT as high at 1650F in a non-turbocharged engine.   The highest I've ever seen is maybe 1500-1550.

Low compression engines will get much hotter than high compression ones. A Ford Model T will apparently have its exhaust manifold glowing red for instance, with its mighty 4 to 1 compression. Trivia, it’s was originally 4.5 to 1, but later dropped to 3.98 to 1 due to low octane fuel. Imagine how bad fuel had to be for 4.5 to 1 to be too high  

However I have never heard of an engine EGT limit, turbo engines often have TIT limits, but that’s a turbo not an engine limit.

Back in the day the numbers were left off of EGT gauges intentionally, because numbers aren’t relevant, just how much cooler than peak is, then someone put numbers on theirs inferring theirs was superior I’m sure and of course that began the concern of temps.

I wonder where the redline came from on these gauges? However they got there, I’m pretty sure your not allowed to exceed that red line, assuming of course the POH says as I assume it does that redline is maximum.

 

 

[EricJ]

42 minutes ago, 0TreeLemur said:

I've never seen EGT as high at 1650F in a non-turbocharged engine.   The highest I've ever seen is maybe 1500-1550.

My JPI was installed about five years ago and the EGTs have gradually gone up over time.   I'm guessing this is due to the probes or something in the system aging, as they're doing it pretty uniformly and compressions, borescopes, CHTs, and everything else have remained normal.   If I lean through peak now my hottest cylinders will show high enough EGTs to go in the yellow range on the JPI, basically about 1580F or so.    It's pretty weird, but it's made me keep a close eye on everything else, which has remained fine.   I figure if it keeps doing it whatever it is will eventually make itself known and I can change them out, or maybe it's just what it does.

 

[PT20J]

That redline is suspicious. 1650F is a common TIT limit (turbos have close tolerances, the turbine spins at very high rpm so there is a lot of centrifugal force and the metal expands when heated. At some temperature, the turbine wheel will drag on the case). Perhaps that gauge marking is a holdover from a TIT gauge.

If there is no limit listed in the Limitations section of the AFM, then there is no limitation according to the FAA (the limitations section of the AFM is the only part of that document approved by the FAA and exceeding an operating limitation listed in the AFM is a violation of FAR 91.9).

In the picture posted, the Mauritz EGT gauge shows an EGT of 1552 F while the engine monitor is showing EGTs over 100 F  lower. I would just ignore the Mauritz EGT gauge.

Skip

[0TreeLemur]

2 hours ago, EricJ said:

My JPI was installed about five years ago and the EGTs have gradually gone up over time.   I'm guessing this is due to the probes or something in the system aging, as they're doing it pretty uniformly and compressions, borescopes, CHTs, and everything else have remained normal.   If I lean through peak now my hottest cylinders will show high enough EGTs to go in the yellow range on the JPI, basically about 1580F or so.    It's pretty weird, but it's made me keep a close eye on everything else, which has remained fine.   I figure if it keeps doing it whatever it is will eventually make itself known and I can change them out, or maybe it's just what it does.

 

That is weird.  Thermocouples are pretty darn simple.  Not much to go wrong until they fail.   Hangar fairies moving them closer to the cylinders while you sleep?

The new JPI we installed in March came with two faulty EGT thermocouples that read about 600F low compared to the other two.   Yet in Lean Find mode they responded perfectly.

[0TreeLemur]

This is an interesting figure.   I've wondered if anyone ever put a go-pro under their engine and taken video in flight?

Steel melts at about 2200F.

Stolen from hearth.com. (sorry)

 

[ilovecornfields]

1 hour ago, 0TreeLemur said:

This is an interesting figure.   I've wondered if anyone ever put a go-pro under their engine and taken video in flight?

Steel melts at about 2200F.

Stolen from hearth.com. (sorry)

 

So when I see a lemon exhaust I should get worried? I’ll see if I can get my fat head out the storm window.

@PT20J, yes, the JPI does consistently show about 100 dF lower. I guess I don’t know which one to believe. My understanding was that they were in different places so I’m not sure which one matters.

I’m less worried about POH limits and more concerned about what (if anything) might happen if I get too hot.

[Niko182]

17 minutes ago, ilovecornfields said:

So when I see a lemon exhaust I should get worried? I’ll see if I can get my fat head out the storm window.

@PT20J, yes, the JPI does consistently show about 100 dF lower. I guess I don’t know which one to believe. My understanding was that they were in different places so I’m not sure which one matters.

I’m less worried about POH limits and more concerned about what (if anything) might happen if I get too hot.

The probe for the EGT on the moritz is significantly lower on the exhaust than the probes for the jpi. The moritz probe gets the EGT heat from all 3 exhausts where the exhaust combines the cylinders 2, 4, and 6. JPI gets each individual much closer to the valve. I’m guessing it’s hotter because at that point in the exhaust it probably is higher. Similar to the way TIT on a turbo engine is hotter than the EGTs even though the TIT probe is further away from the valves than the EGT probes are.

[FlyingScot]

9 hours ago, 0TreeLemur said:

 

 

Interesting fact: foundry workers get very good at visually estimating the temp of the melt from its color temperature. Old timers can pretty regularly do this to +/-50 degrees. 

[PT20J]

9 hours ago, ilovecornfields said:

I’m less worried about POH limits and more concerned about what (if anything) might happen if I get too hot.

I understand. But my point was that if Mooney (or the FAA) had a concern, it would have been listed in the AFM. 

[PT20J]

10 hours ago, Niko182 said:

The probe for the EGT on the moritz is significantly lower on the exhaust than the probes for the jpi. The moritz probe gets the EGT heat from all 3 exhausts where the exhaust combines the cylinders 2, 4, and 6. JPI gets each individual much closer to the valve. I’m guessing it’s hotter because at that point in the exhaust it probably is higher. Similar to the way TIT on a turbo engine is hotter than the EGTs even though the TIT probe is further away from the valves than the EGT probes are.

That explains the difference. The instantaneous EGT is much hotter than the time-averaged EGT shown by the gauge, but it comes in pulses. Although the original gauge is installed farther downstream where the EGT should be lower it is receiving more frequent pulses by combining the exhausts of multiple cylinders which will cause the gauge to read higher. 

[A64Pilot]

12 hours ago, ilovecornfields said:

So when I see a lemon exhaust I should get worried? I’ll see if I can get my fat head out the storm window.

@PT20J, yes, the JPI does consistently show about 100 dF lower. I guess I don’t know which one to believe. My understanding was that they were in different places so I’m not sure which one matters.

I’m less worried about POH limits and more concerned about what (if anything) might happen if I get too hot.

Pic of a twin Cessna Turbo in flight

 

[A64Pilot]

3 hours ago, PT20J said:

I understand. But my point was that if Mooney (or the FAA) had a concern, it would have been listed in the AFM. 

Picking nits here, but I believe gauge markings are considered placards, and the AFM and placards both are mandatory.

I’m not disagreeing with you on ignoring the redline though, I do wonder why it’s there.

[Hank]

15 hours ago, 0TreeLemur said:

Steel melts at about 2200F.

Depends upon the alloy. I've heated some machined tool steel parts to 2200ºF in a furnace as part of the hardening process. They didn't melt . . . .

[Shadrach]

5 hours ago, FlyingScot said:

Interesting fact: foundry workers get very good at visually estimating the temp of the melt from its color temperature. Old timers can pretty regularly do this to +/-50 degrees. 

the exhaust will never see anything approaching the actual EGT number. There is a thermal barrier between the metal and gas. If not for this barrier, pistons would not survive combustion (> 3000°). Detonation disrupts said barrier allowing for the rapid increase in piston temperatures that occurs before they get real cool again…

The dark glow that you see through the louvers on the nacelle of a turbo twin in cruise is downstream of the individual cylinder risers it is the culmination of all of the heat from all of the exhaust causing a glow aft of the collector.