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High EGT's (1500+)

RhinoDrvr

Well Known Member
Hi all,

I've listened to Mike Busch's webinars and such, and have gathered that EGT is meaningless on a non-turbo Lycoming, and is simply a point of reference for setting fuel flow.

That said; at low altitude, LOP, my EGT's are around 1550 F, which turns my G3X engine monitor from green to yellow. I can reset this threshold, but before I do I wanted to make sure I wasn't missing some limit.

I know in turbocharged installations 1650 is generally referenced as maximum turbine inlet temperature (TIT), but I obviously don't have a turbine to worry about. So, is it safe to say that my EGT's of 1550 are completely fine, and I should just reset the yellow caution to 1600 degrees, and the redline to 1650?

The high EGT's began occurring when I timed my PMAG's 1 tooth after TDC, which makes sense. Less advance = higher EGT's, and lower CHT's.

TL,DR - Is it acceptable to set the caution and warning ranges on the G3X to 1600 and 1650 degrees respectively, or are EGT's in the high 1500's something to be aware of. I don't want to unknowingly cause damage or excessive wear to my exhaust components.
 
Hi Evan, Dynon Skyview comes also with preset green/yellow/red EGT ranges. i found that annoying and changed it to all green.

As you said absolute EGT values for us normally aspirated are meaningless. Imagine you have installed your EGT probes one foot lower... you get the idea. i see no problem and your 1500...1600 indications sound just normal.
 
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I can give you a data point - I can get to right at 1500f EGT when running about 10gph at 4500 or 5500 ft WOT. At 16GPH I show about 1180f.

Not saying this is right or good or confirms your setup is ok. I don't run LOP for more than just short tests as I have not really flown much out of my area.

My pmags are programmed like this using the eicommander:

ADV max: 33.6
ADV shf: -1.4
 
Re time the P-Mags to TDC. Also check all of your pipes from the inlet manifold to the P-Mags.

We had exactly the same issues accompanied by low power. Brad was brilliant and said check for leaks in the pipes, if no leaks, re time to TDC.

We found a pipe had come off.

This stops the P-Mags from advancing, they run in base get yourself home mode but are well retarded. Hence you have burning fuel leaving the cylinders on the exhaust. At that, your egt probes will be toast !
 
Re time the P-Mags to TDC. Also check all of your pipes from the inlet manifold to the P-Mags.

We had exactly the same issues accompanied by low power. Brad was brilliant and said check for leaks in the pipes, if no leaks, re time to TDC.

We found a pipe had come off.

This stops the P-Mags from advancing, they run in base get yourself home mode but are well retarded. Hence you have burning fuel leaving the cylinders on the exhaust. At that, your egt probes will be toast !

Mike, I assume "a pipe had come off" means you had one leaking intake gasket. It would make little or no advance difference in cruise at WOT, as the deltaP across the leak would only be equal to intake tract loss (about 14.4" H2O total for the standard Lycoming horizontal system, for example), and pretty much limited to the tract with the leak...which may or may not be the one tapped for manifold pressure. At low altitude, throttled, the deltaP would be higher, but the effect is not hidden. The pilot's manifold pressure gauge is showing the same pressure seen by the P-mags. The P-mags care not if the pressure is the result of altitude or a leak, or a properly throttled intake. They just advance per the pressure seen on the MP gauge, and RPM.

Rebranding standard Lycoming timing as "base get home mode" is spin worthy of a politician. Standard timing (base P-mag timing) is not "well-retarded". It's normal.

At normal timing, combustion is complete before the the exhaust valve opens. With advanced timing it's complete even earlier. There may be fuel in the exhaust stream, but that would be a function of a mixture setting on the rich side of peak, where there wasn't enough available oxygen to combine with all the carbons. Any burning is limited to a few strays which didn't get married earlier in the game. Indicated EGT is a function of pressure at exhaust valve opening. And given the OP is concerned with high EGT, I believe we can safely assume he is not full rich. Peak EGT closely corresponds to stoich, where combustion is fastest.

Consider the operating principle of the common O2 sensor.
 
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Assuming this is a new condition, I would be looking at a timing error or inop condition on one of the Pmags. 1550 LOP seems high to me, though I understand that each setup is different. Not a problem being that high, only that it is an indication that your timing is too retarded. Only time I have seen 1500+ when LOP and lower power settings is when one ignition went bad. Running the cylinders on one plug substantially retards the effective timing and will drive the EGTs a good 100* above normally.

Also possible that you took out too much timing and are now well below optimum and leaving power on the table. Only way to tell is with a timing gun.
 
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The sense pipe from the inlet manifold had split and detached from the T piece between the mags. The rest is what Brad said as best as I can remember.

In our case, when you got to altitude and the P-Mag saw reducing pressure naturally, it must have advanced.
 
All,

I know why the EGT is at 1550. The PMAG’s are timed 1.4 degrees before TDC which equates to a base timing of 23.6 degrees BTDC vice Lycoming’s recommended 25 degrees.

This limits the PMAG’s max advance on the top end, however, and makes it easier to control CHT’s (they won’t exceed 400 now even during a VX climb on a 100 degree day.

As far as power loss, I can’t tell, so I don’t care. I’d rather not stress my engine with more advance than is necessary for a power advantage that I cannot detect in an airplane that is over-powered as is.

I did have an intake leak, but fixed it with the SDS intake gaskets. I’ve conducted the in-flight lean test, GAMI spread test, and in flight mag-checks, and all show good results.

I’m seeing the 1550 number at peak EGT, and only at low altitudes (below 4000’). At high altitude peak EGT is lower (1450 or so). I normally cruise around 60% power for economy, and about 25 deg LOP, which puts me around 1525 EGT at low altitudes. Just want to confirm that I’m not damaging any exhaust components by tooling around with EGT’s that hot. Up high (8000-12000) where I normally cruise, EGT’s at 25 LOP are closer to 1425, which is more like in line with what I expect (and this is due to the PMAG’s advancing at high altitude and reduced MP).
 
Evan,

Some thoughts:
- pMag timing advance if much more about cruise efficiency than power. For that matter, full rated power (take off) timing with a pMag set per the instructions (at TDC for parallel valve engines) is about the same as a standard mag.
- I fully agree that timing the pMag at something ATDC will result in lower CHTs, but this is at the expense of power and fuel efficiency. You can achieve the same CHT reduction with the pMags set at TDC if you pull back on the throttle and/or keep the mixture knob in.
- If your mission is to win a time to climb competition, retard the timing as you don’t care how much engine efficiency you a loosing along with wasted fuel. If you have a more rounded mission, time the pMags per the installation instructions and run with the jumper in. The jumper in provides timing from 25 degrees to 34 degrees BTDC (at cruise RPM) - I have found no data that suggest more advance is beneficial. Now use the other tools available to you to keep CHTs below your target (mixture, throttle and climb speed).

Get the most out of every drop of fuel you put in the engine.

Carl
 
The sense pipe from the inlet manifold had split and detached from the T piece between the mags.

Ahhh, split rubber or plastic tubing? "Pipe" suggests something different on this side of the pond.

With an open port, the P-mag would not advance from base timing at low altitude. With the engine throttled at low altitude, it would raise EGT as compared to EGT with advanced timing, although I don't think it would be a huge amount, as again, the engine is throttled. Regardless, you made a good suggestion; the OP should indeed check to see if perhaps the tube got knocked off a nipple when he re-timed, or just wasn't re-connected after the blow.

That said, base timing is not retarded or a limp home. It is more or less the same as standard fixed timing. Calling it anything else is BS, and I don't care who said it.

Returning to Evan's interest...

Just want to confirm that I’m not damaging any exhaust components by tooling around with EGT’s that hot.

Unlikely, for several reasons.
 
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All,

The PMAG’s are timed 1.4 degrees before TDC which equates to a base timing of 23.6 degrees BTDC vice Lycoming’s recommended 25 degrees.
.

What drives you to that conclusion? You said you moved one full tooth from the TDC line. By my math, that is ~2.5 degrees (149/360) or 3* if you have a 122 tooth gear. If you didn't accurately measure it, it could easily be 3 degrees retarded.

I also agree that 1550 if fine though with the oil coking issue in Lyc exh valve guides I do believe that lower is better. Anyghing that keeps the oil in the guides from reaching the oil's oxidation temp is a good thing.
 
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Sounds high to me, I typically run around 1350 ish, 1450 or a bit less is close to my peak.
I generally run ROP for best power, 20deg fixed timing on my 370 with HC 9.6.

1550-1600 seems rather high, the exh valve is going to be getting hot. Not a great combo if CHT's are up at 400.
 
What drives you to that conclusion? You said you moved one full tooth from the TDC line. By my math, that is ~2.5 degrees (149/360) or 3* if you have a 122 tooth gear. If you didn't accurately measure it, it could easily be 3 degrees retarded.

I also agree that 1550 if fine though with the oil coking issue in Lyc exh valve guides I do believe that lower is better. Anyghing that keeps the oil in the guides from reaching the oil's oxidation temp is a good thing.

You are 100% correct. I have a 149 tooth ring gear, so 2.5 degrees is the number I was referencing. My recollection was incorrect.

I did just move away from the Devil’s armpit (Mojave desert) to a more temperate climate, so I could retime the PMAG’s at peak and see how that changes things. That said; I still don’t like the full 37 degrees of advance that they provide timed that way.
 
Sounds high to me, I typically run around 1350 ish, 1450 or a bit less is close to my peak.
I generally run ROP for best power, 20deg fixed timing on my 370 with HC 9.6.

1550-1600 seems rather high, the exh valve is going to be getting hot. Not a great combo if CHT's are up at 400.

Thanks for the reply Walt. Up at altitude, I see the same. About 1400 is my cruise EGT, which is about 50 degrees LOP. CHT’s are no problem (330-360. 380 in a Vy climb). It’s just down low where the PMAGs are a little retarded from 25 degrees that the LOP EGT’s climb up to 1500.
 
quote: Just curious, have you measured the distance of your probes from the engine?

I haven’t. Never really cared about my EGT’s until I saw them above 1500

that's wat i wanted to express in my first post... your absolute EGT numbers are somewhat meaningless. that applies if you run your LOP procedures and it also applies if you're about to compare these numbers with others. that's the reason why some old fashioned EGT gauges didn't even show real numbers.

if you see somebody else EGT's running 200 F or so lower, that doesn't mean anything as you don't know how different are these probes installed on the exhaust.

well, if your EGT's change because of altered ignition timing... that's a complete seperate topic.
 
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FWIW, quick experiment today...set 2400, throttled for 65% at 3000 ft, leaned to peak EGT. Shutting down one ignition was all it took to push EGT from roughly 1450 to 1550.

Someone with SDS ignition could easily dial 2.5 less degrees in flight and see how much it changes EGT
 
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At my next oil change I’ll likely time my PMAG’s 1/2 tooth aft of TDC, and see what effect that has. Currently I can climb at Vy of 90 kts to 10,000’ on a 70 degree day and keep the hottest CHT at 395. Which is nice, but likely unnecessarily cool. If I can take back 1.5 degrees of timing and keep CHT’s under 400 with a 120kt climb that would suit me fine as well.
 
Inflight (P) Mag Check

Hi Evan,

On my angle valve (mags), 2 or 3 degrees change in timing does not cause that much change in EGT. Also, unless your probes are literally right at the exhaust flanges, 1550 EGT seems pretty high to me. Have you tried doing an in-flight (P)Mag check when in your low altitude high EGT operational mode to ensure both PMag's are functioning? As Dan stated, the loss of 1 ignition system will create a pretty large increase in EGT's.

Skylor
 
Skylor,

I did an in-flight mag check, and the EGT's rise from 1550 or so with each ignition off.

I'm 99% sure that it's a timing thing, because as I climb in altitude up to 8000-10000 feet where the PMAG's start advancing significantly, the peak EGT comes down to around 1450, and I end up cruising around 1400-1425 at 25-50 LOP.

I wonder if my EGT probes are closer to the cylinders than others are? I'll take a measure next time the cowl is off.

Hope all is well in socal! We need to do some flying soon!
 
Normal

I think what you are seeing is pretty normal. On my dual p-mag (no jumper) IO-375 I see EGT's on takeoff on a standard day that are around 1550. My CHT's are generally below 350. Timed about 1 degree after TDC. To get the EGT probes all the same distance they are about 1.7inches from the exhaust flange. 350 hrs and no burned probes.
 
I think what you are seeing is pretty normal. On my dual p-mag (no jumper) IO-375 I see EGT's on takeoff on a standard day that are around 1550. My CHT's are generally below 350. Timed about 1 degree after TDC. To get the EGT probes all the same distance they are about 1.7inches from the exhaust flange. 350 hrs and no burned probes.

That sounds really high, curious what your fuel flow is as I see about 1250 at TO pwr full rich with Bendix mags.
 
Data point Walt...probes how far down from the gasket?

Did that around oh around 18 yrs ago, but to the best of my recollection, I followed the EI install manual and put them at the recommended 1.5".
(still running the original EI EGT probes)
 
Hi Evan,

Also, unless your probes are literally right at the exhaust flanges, 1550 EGT seems pretty high to me.

Skylor

Do you have any empirical evidence to support this statement or is it just a guess. I do not have any data on the placement of EGT probes and resultant temperatures but I would be very interested if someone else does.
Intuitively I am inclined to imagine that at temperatures approaching 1500 degrees F just very small incremental movement of the probe up or down the exhaust pipe would have a significant effect on the EGT readings. In a previous thread someone claimed that Vetterman told him that just 1/16" movement of the EGT probe could cause a 50 degree F change in EGT.

Typically Vans builders tend to place their EGT probes about 3" down from the flange. The problem there is that 3" down puts you into different bends in different pipes. This also probably tends to produce significant variations in EGT temperatures from one cylinder to another.

Interesting topic.
 
Did that around oh around 18 yrs ago, but to the best of my recollection, I followed the EI install manual and put them at the recommended 1.5".
(still running the original EI EGT probes)

Most manufacturers recommend 2" to 4". Common theory says closer to the port should be hotter, but it appears to be untrue in your case. As you stated EGT with mags, that pretty much leaves mixture as the only variable.

Here's an old Busch column on EGT. There are a few things with which I disagree, but the overall theme appears solid...initially EGT systems didn't have any sort of absolute temperature readout. They were intended to simply reference peak. Fixation on absolute temperatures was a later development driven mostly by marketing.

I also like a memorable analogy:

The temperature you report to the pilot is not exhaust gas temperature (which is gyrating crazily 20 times a second), but rather exhaust probe temperature (which is stable but related to actual exhaust gas temperature in roughly the same fashion as mean sea level is to high tide).
 
Most manufacturers recommend 2" to 4". Common theory says closer to the port should be hotter, but it appears to be untrue in your case. As you stated EGT with mags, that pretty much leaves mixture as the only variable.


[/I]

EI (Electronics International) still recommends 1.5" and I consider them to be one of the premier manufacturers of engine monitoring equip.. My impression is other manuf probes are not as robust hence the lower temps (further away) will make them last a bit longer. I know Garmin and I think JPI as well both use the thinner fast response Alcor probes.
 
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EI (Electronics International) still recommends 1.5" and I consider them to be one of the premier manufacturers of engine monitoring equip..

So do I. However, they may have changed their recommendation...
 

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Returning to the OP's interest...

I know why the EGT is at 1550. The PMAG’s are timed 1.4 degrees before TDC which equates to a base timing of 23.6 degrees BTDC vice Lycoming’s recommended 25 degrees.

Nope. Reducing advance by 1.4 or 2.5, or even 5 doesn't appear to make a big difference.

Had a quick run down to Mobile this AM, so I flew two tests, one each way, leaning to a stable peak at 65%, then switching ignition timing from 23 BTDC to 28 BTDC. The goal was to determine the resulting EGT change. Note this is a 5 degree shift, a bit more than the OP's reset, and (caveat) it's a 390 angle valve. The OP had specified low altitude, so I captured both 8500 ft and 3500 ft. Timing change appears to drive EGT approximately 5 to 6 degrees F per degree of timing.

First 8500. The average EGT change is about 24F.

8500%20ft%20-%2023%20vs%2028.JPG


Then later, at 3500. The average EGT change was 31F

3500%20ft%20-%2023%20vs%2028.JPG
 
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