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High EGT w/ Low CHT?

ChuckGant

ChuckGant

Well Known Member
I have had this happen a couple of times now...
On the #1 cylinder, I have gotten EGT above 1500 degrees while having the lowest CHT. I know they aren't directly related, but what causes it and is this something I need to be concerned about?

Also, what temperature are you guys using for a High EGT warning on your EFIS/EIS? Mine was set at 1500 by the builder.

I've been playing around with LOP operations. When I get too lean, the engine starts popping? Obviously I don't want to run it like that, but was wondering what exactly is going on.

Thanks,
Chuck

IMG_5111_zpsjpyen6ij.jpg
 
Is this in flight? I assume so, but it looks like you are well under 50% power. I would suspect a faulty probe, either EGT or CHT, but most likely EGT. It could be a wiring error, a shorted wire or a loose wire, or it could be the head of the probe itself. In most planes I fly, I can't get to 1500 on EGT anywhere close to that power setting. Running lean at high power can approach that, but at hat power setting I would expect peak around 425 or lower. For hat matter, 2 and 3 look suspiciously high too.

For EGT I usually set yellow at 1400 and red at 1450-1475. I don't like to run for an extended length of time above 1400, so I run ROP with the leanest at 1400 or LOP with the richest at 1400.
 
Need more info

the power looks too low for evaluation, try MP of 25" and fuel flow of about 10 gpm; then we can better judge. Your readings look OK, so far. Also please say altitude of next test. One minute of higher power should be enough, or use minimum of 23" mp if you prefer.
 
It's relative

EGT temp isn't too important as a stand alone number, there isn't a too high or normal, nor even a standard install location relative to the exhaust port. When comparing numbers with other people you don't even know where their probes are installed, an inch can make a big difference.
It's value is relative to fuel flow, we want to know when it peaks, not where it peaks, so we can adjust from there rich or lean, and we hope they all peak at the same fuel flow. If they do we know all cylinders are getting the same fuel flow.
Tim Andres

https://www.savvyanalysis.com/articles/understanding-cht-and-egt
 
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I agree that it's hard to tell anything definitive at such low power settings, however:

1. If this is happening LOP, you may simply be getting to the point where cylinder #1 has a plug dropping out. Popping from the exhaust is also an indicator that you're running too lean.

2. You may have an induction leak on cylinder #1 causing it to be overly lean at low manifold pressures.

3. A poorly sealing or sticking valve could result in high EGT and low CHT.



ChuckGant said:
I have had this happen a couple of times now...
On the #1 cylinder, I have gotten EGT above 1500 degrees while having the lowest CHT. I know they aren't directly related, but what causes it and is this something I need to be concerned about?

Also, what temperature are you guys using for a High EGT warning on your EFIS/EIS? Mine was set at 1500 by the builder.

I've been playing around with LOP operations. When I get too lean, the engine starts popping? Obviously I don't want to run it like that, but was wondering what exactly is going on.

Thanks,
Chuck

IMG_5111_zpsjpyen6ij.jpg
Click to expand...
 
Thanks for the input guys. The reason the power is so low is that I was in a descent at the time. In level flight, at 22"/2350 and about 9.0 gph and LOP, the EGTs were all in the mid 1300s. I then pulled power back for the descent and got the alarm at 1500 degrees.

Unfortunately, my airplane is in for it's conditional inspection and I'll be out of town for awhile, so I won't be able to re-test it for a few weeks.

I appreciate the input. I'll see what happens next time and try to get more specific details.
 
Intake leak

Your symptoms are indicative of an intake leak. They always show up when reducing the power for descent.

Vic
 
I'll put in a word for the Savvy Analysis Pro service, which is very inexpensive and can answer these questions.

It's important to note that the first thing they have you do is fly a flight test regime and send them the data. THEN send them this data.

It's a great service.
 
I agree with others that an intake leak would cause a cyl to go lean. However, the EGT looks to be in the area of peak. If the lean condition was the cause for the low CHT, wouldn't we expect to see the EGT lower than others, given that it is much leaner? hoping I can learn something here along with the OP.
 
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skylor said:
I agree that it's hard to tell anything definitive at such low power settings, however:

1. If this is happening LOP, you may simply be getting to the point where cylinder #1 has a plug dropping out. Popping from the exhaust is also an indicator that you're running too lean.

2. You may have an induction leak on cylinder #1 causing it to be overly lean at low manifold pressures.

3. A poorly sealing or sticking valve could result in high EGT and low CHT.
Click to expand...
It does sound like an induction leak could be occurring. There is quite a spread of EGT readings between the 4 cylinders. Not only is the highest 1507 odd but the lowest 1391 as well. The relative spread is greater than I would like with my engine for sure.

I also wanted to point out for those who may not be familiar with the GRT display, the fuel flow reading is indicating 5.9 gph in the OP (upper left corner of the screen).
 
Following a discussion via PM, I want to clarify the point I was making above (or below, depending on how your threads are organized). In theory, there is nothing wrong with running EGT's over 1400. In fact, on a Turbonormalized IO-540 in a Cessna 182 the EGT's are very often well over 1400. My point is that, in practice, peak is often between 1425 and 1450 at or below 75% power. In this case, 1400 gives me 25-50 ROP or LOP, which is where I like to run. So, for those who think I was saying it's dangerous to see EGT's above 1400, I wasn't. I was just saying that an easy way, assuming probes are appropriately placed and working correctly, to keep in a safe zone, for me, is to be at or below 1400, whether ROP or LOP. In fact, at lower power settings, the peak often only reaches 1400 barely, and I often will run very close to peak, but that's usually very low power settings, like 18" or less.

Back to the topic at hand, while it could be a plug not firing or something like that, one thing that I would recommend checking is the wiring and the probe itself. Things are not going to blow up even if that is the actual temp, though.
 
Peak?

lr172 said:
I agree with others that an intake leak would cause a cyl to go lean. However, the EGT looks to be in the area of peak. If the lean condition was the cause for the low CHT, wouldn't we expect to see the EGT lower than others, given that it is much leaner? hoping I can learn something here along with the OP.
Click to expand...

If the number 1 cylinder is so lean that a plug has dropped out, or the EGT has begun to rise again from the very slow mixture burn, it's possible to see temps in the 1500F range while the cylinder is operating well lean of peak.

Skylor
 
Do you have electronic ignitions?
Click to expand...
Yes I have a PMag and an EMag.

If the number 1 cylinder is so lean that a plug has dropped out, or the EGT has begun to rise again from the very slow mixture burn, it's possible to see temps in the 1500F range while the cylinder is operating well lean of peak.
Click to expand...
Is this bad?

I will do a controlled test flight after we get it out of annual and see what it does. Thanks again.
 
ChuckGant said:
Is this the same as the GAMI Lean test?
http://www.gami.com/gamijectors/leantest.php
Click to expand...

A HiLo test (spelled various ways) is a GAMI Lean Test done at two altitudes. First, go up high, say 10k, and do a Lean Test. Then go down low and set the MP at the same value is was at high altitude. Repeat the Lean Test. Your cylinders should peak in the same order. If not, you may have an induction leak in the vicinity of the cylinder that peaked first at low altitude.

For instance, if you do the test at 10k and they peak in order 2,4,1,3 and you repeat it at 2000 (throttled back), where they peak 1,2,4,3, your leak is closest to #1. This happens because, while the other 3 cylinders are sucking against a partially closed throttle, the 4th (#1 in this case) gets additional air through the leak, making it leaner.

Given the timing of this indication (only when throttled back), I think an induction leak is more likely than a bad plug or a bad probe.

So, if I were in your shoes, I'd go out and do a high altitude LOP mag check -- not because I think it's ignition-related, but it's easy to rule out -- and a HiLo test before I threw any money at it. And, assuming you have GAMIs, I'd send the data to them rather than Savvy.

There are a lot of people here who know more than I do about such things. I've just had a lot of experience with engine issues.
 
As you are running pMags (good choice), and considering the other variables at such this low power, I think your EGTs are high but not out of line. At this power setting you will be getting the most timing advance available (39 degrees if you selected the more advanced curve) and I would expect high EGTs. While your numbers are perhaps 100 degrees higher than my experience I'd look at other factors to explain - such as excessively lean and/or EGT probe placement.

What I would do:
- first do a ground check with the engine at fast idle (1000 RPM), and lean. Watch each cylinder EGT. If one goes lower and the other go higher you either have an intake pipe leak or a clogged spider (as I discussed in my stuck exhaust valve thread). If either of these are at issue you may also experience a "barking" exhaust.
- select the lower advance curve on both pMags (34 degrees) and note the change.
- do a GAMI spread (fuel flow first to peak minus fuel flow last to peak) at typical cruise conditions, say 6500', 23.5" and 2350 RPM.
- do another GAMI spread at the 39 degree advance setting (remember the setting only changes before starting the engine).

From this data verify no gross air leaks, balance the injectors and fly on.

Carl
 
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