EGT: How high is too high?

FORANE

FORANE

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FORANE
I know there are recommended limits for CHT's.
Are there similar limits for EGT's?

I know probe position will be a factor in the EGT. I have heard the maximum actual EGT is less important than using the trend to find peak.

At low level (as in 2000-3000 msl) my O-320 runs EGT's around 1600+ compared to typical cruise above 8000 msl where the EGT's run 1350-1400. On one 1+ hour trip in the middle of winter with a solid overcast of 2000-3000 agl with known ice in the overcast I elected to scud run under the overcast. I ran EGT's around 1600 the whole way and could not get them lower. About the time I got to destination, I had lost compression on one cylinder which I attributed to the high EGT's. We did not borescope it to know for certain.

So, my question is, how high is too high? Or is there a too high?
 
Might be your probes or display. The only way to increase egt is to decrease timing or lower compression. Other than that you got the same engine as the other 0-320s. CHTs is the important reading as far as absolutes.

Egt only used to tell how far ROP or LOP you are and maybe used to help aid in troubleshooting.
 
Nope. High EGT didn't cause your loss of compression. Your loss of compression caused the high EGT. One such mechanism would be a burned exhaust valve. Those are generally caused by dirt getting caught in the seat. It was an icy day according to your post. Running the carb heat continuously by any chance?
 
MAKG1 said:
Running the carb heat continuously by any chance?
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No.
I turned it on a time or 2 which is something I almost never do but not continuously.
Also, by loss of compression, I should clarify that there was zero compression on the cylinder. At full power I could only make about 2100 rpm's and it shook the plane significantly. This occurred abruptly.
Another clarification, I was running partial power the whole trip.
 
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Btw, you didn't mention what type of egt measuring system you have is it a multi point digital or single point? And MAKG1 is spot on....

Research mike busch egt myth....it's a great webinar
 
Aaronk25 said:
Btw, you didn't mention what type of egt measuring system you have is it a multi point digital or single point? And MAKG1 is spot on....

Research mike busch egt myth....it's a great webinar
Click to expand...

I enjoyed that webinar. It helped out quite a bit.
 
Aaronk25 said:
Btw, you didn't mention what type of egt measuring system you have is it a multi point digital or single point? And MAKG1 is spot on....

Research mike busch egt myth....it's a great webinar
Click to expand...
Aerospace Logic EGT-100-4P
instruments-egt-gauges-aerospace-logic-aerospace-logic-egt-100-4.jpg
 
FORANE said:
No.
I turned it on a time or 2 which is something I almost never do but not continuously.
Also, by loss of compression, I should clarify that there was zero compression on the cylinder. At full power I could only make about 2100 rpm's and it shook the plane significantly. This occurred abruptly.
Another clarification, I was running partial power the whole trip.
Click to expand...
Sounds like you stuck a valve.
 
Witmo said:
Sounds like you stuck a valve.
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Yes, that is what we thought it was.
The A&P who helped me with this matter when I was away from home did not try to confirm this however. We just pulled the jug and replaced it.
 
Many people don't care. I figure using similar personal limits as I'd do for turbos makes sense, so I try to keep below 1550F. That's about what I'm normally running in cruise.

However, in your case I think the issues were separate. If you couldn't get EGT below 1600 (I'm guessing on one cylinder?) you had something else wrong already. Full rich should be more like 1300ish. I also don't know what you were running for MP, but that all tells me something else went wrong. Burned/stuck valve, etc.

Different theories on EGTs. Mike Bush says it's a myth that high EGTs cause problems, but it seems like the people I talk to who run high EGTs a lot (mostly turbos) have more cylinder and exhaust issues than people who don't. I haven't done a scientific study on this, just my observations, so take it for what it's worth.
 
Ted DuPuis said:
Many people don't care. I figure using similar personal limits as I'd do for turbos makes sense, so I try to keep below 1550F. That's about what I'm normally running in cruise.

However, in your case I think the issues were separate. If you couldn't get EGT below 1600 (I'm guessing on one cylinder?) you had something else wrong already. Full rich should be more like 1300ish. I also don't know what you were running for MP, but that all tells me something else went wrong. Burned/stuck valve, etc.

Different theories on EGTs. Mike Bush says it's a myth that high EGTs cause problems, but it seems like the people I talk to who run high EGTs a lot (mostly turbos) have more cylinder and exhaust issues than people who don't. I haven't done a scientific study on this, just my observations, so take it for what it's worth.
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At low level - as in just 1-3k msl - even with full rich I will run 1600 or so on all cylinders. I do not know why this happens. That was the case on the flight when this occurred and was the only reason I even touched the carb heat at all on the flight - to see if it changed the EGT's.
I do not recall what I was running for MP's but I was throttled back to around 50-60% most of the flight. At the time of this flight I had a fixed pitch prop on the plane.
 
Ok, so that might have some more to do with it if you were throttled back, but still seems high.
 
Stupid question time:
How will low compression cause high EGT? I thought higher EGTs meant you were getting more complete fuel burn? With low compression, wouldn't you be getting less (or no) fuel burn? Or is it that an exhaust valve stuck open allows the hot burnt fuel to escape out the exhaust rather than pushing down on the cylinder?

My O360 generally runs in excess of 1500 in cruise.
 
JOhnH said:
Stupid question time:
How will low compression cause high EGT? I thought higher EGTs meant you were getting more complete fuel burn? With low compression, wouldn't you be getting less (or no) fuel burn? Or is it that an exhaust valve stuck open allows the hot burnt fuel to escape out the exhaust rather than pushing down on the cylinder?

My O360 generally runs in excess of 1500 in cruise.
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If you would have watched that video I posted that Mike Busch did, you would have the answer to this.
High EGT is wasted energy going out the exhaust.
Tony
 
1600vw said:
If you would have watched that video I posted that Mike Busch did, you would have the answer to this.
High EGT is wasted energy going out the exhaust.
Tony
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I fully intend to watch that video when I am not at work and when have time to pay attention and I can take notes.
Oh, and thanks for posting it. I am looking forward to learning from it.
 
FORANE said:
At low level - as in just 1-3k msl - even with full rich I will run 1600 or so on all cylinders. I do not know why this happens. That was the case on the flight when this occurred and was the only reason I even touched the carb heat at all on the flight - to see if it changed the EGT's.
I do not recall what I was running for MP's but I was throttled back to around 50-60% most of the flight. At the time of this flight I had a fixed pitch prop on the plane.
Click to expand...

Mike explains what you are seeing in that video I posted. If you Lean you can reduce this temp by changing the timing of the flame front.
Very good info in that webinar.

Tony
 
The higher the compression the more energy extracted from the fuel, lower compression less energy.

This is why a big 6 cylinder turbo lycoming engine with the lowest compression ratio of 7.5 of all (that I am aware of) engines produces the highest egt at 1,750 degrees!

My mooney with a io-360 with the highest compression cylinders of most aircraft produces max egt if 1520 or so. Take off is 1250.


I'd bet money on it that if all your cylinders are "reporting" 1600 degrees that your egt monitor is lying to you. How high does the egt get if you lean until the temp peaks?
 
JOhnH said:
Stupid question time:
How will low compression cause high EGT? I thought higher EGTs meant you were getting more complete fuel burn? With low compression, wouldn't you be getting less (or no) fuel burn? Or is it that an exhaust valve stuck open allows the hot burnt fuel to escape out the exhaust rather than pushing down on the cylinder?

My O360 generally runs in excess of 1500 in cruise.
Click to expand...

If the compression is being lost out the exhaust -- sometimes it is and sometimes it isn't -- then you'll see combustion temperatures in the exhaust itself.

A stuck exhaust valve will do that, for instance. Though it's hard to imagine the exhaust valve sticking like that without also bending the pushrod. A really badly seated exhaust valve will do it as well (burned or severely warped, or perhaps severely recessed). In principle, really bad timing can do that as well; basically the burn has to be still going on when the exhaust valve opens.

For an engine that is working properly, EGT tells you the efficiency of combustion (NOT the engine's efficiency -- that's different). It is not working properly with low compression, bad timing, etc.

FYI, an measurement that more or less tells you directly how the engine is doing is the MP gauge. If it's jittery, don't fly. If it's higher than expected at idle, don't fly. A closely related vacuum gauge is the first order of business when diagnosing automotive drivability problems. It can tell you all kinds of things like sticky valves (at idle), ignition misfires, excessive blow-by, etc.
 
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I'd seen that awhile back. When I clicked it again, I thought there was now way I'm going to spend 1hr40mins watching a boring video.

Guess what?

It wasn't boring and I watched the whole thing.

And I think more of it stuck than when I saw it a few years ago.
 
Jaybird180 said:
I'd seen that awhile back. When I clicked it again, I thought there was now way I'm going to spend 1hr40mins watching a boring video.

Guess what?

It wasn't boring and I watched the whole thing.

And I think more of it stuck than when I saw it a few years ago.
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Its those spouting the myths that will not watch or listen to anything for why should they...They know it all.

I see it all the time in the auto world. A person goes and gets this new part to replace the old part that wore out.

They open the box, take the part out and all paper work in the box gets thrown away, or they never take it out of the box.

Why should they, they just removed such and such part and not one person on earth can tell them how to put it back on for they know how to do it.

Jump forward a few months and this new parts fails. From improper installation. But this person does not know this and calls the part...JUNK. Damn parts today are made like ****.. I hear it all the time.

All one needs to do is ask one question. Did you read the installation instruction that came with the part?

One thing I took away from this video is how one can effect timing somewhat by using the mixture control.

Very interesting video. Mike Busch is the Man for sure. He knows his stuff.

Tony
 
FORANE said:
Yes, that is what we thought it was.
The A&P who helped me with this matter when I was away from home did not try to confirm this however. We just pulled the jug and replaced it.
Click to expand...

It should have been obvious when you pulled the jug whether you had a stuck valve or not.
 
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