High EGT Advice

[zehutiman]

I’ve been flying my airplane (Missile) with a new GI275 for about 1 1/2 months and during the last couple flights, the #4 cylinder EGT has been running about 130 deg hotter than the rest.  The CHT is a bit higher, too.  I can’t find an actual EGT limitation listed for my IO550A, but obviously the 130 deg difference shows something isn’t right.  My research shows that if it was a valve problem, the CHT would probably be lower?  Any thoughts?

PS: during descent, the EGT increased quite a bit — high 1500’s — so I increased the mixture to keep the temps down.  I’ve never paid a lot of attention to the EGT’s and CHT’s during descent, but I’m reminded of Mike Bush’s comments that he leaves the mixture alone after he’s finished leaning at cruise, so it stays the same all the way to landing.

 

 

[N201MKTurbo]

Three things that can cause that (that I know of). 

1.   That cylinder is running leaner than the others.

        Do a lean test and see if that cylinder peaks at the same FF as the rest.

2.   One plug isn't firing in that cylinder.

        Do an in flight mag check and see what the EGTs are on the individual mags.

3.   The sensor is bad.

        Swap the sensors between cylinders. or at least remove and inspect the sensors.

[EricJ]

2 hours ago, zehutiman said:

I’ve never paid a lot of attention to the EGT’s and CHT’s during descent, but I’m reminded of Mike Bush’s comments that he leaves the mixture alone after he’s finished leaning at cruise, so it stays the same all the way to landing.

Remember that Mike Busch flies a turbocharged airplane, and for a normally aspirated airplane you should be adjusting the mixture as you descend or it'll be going lean, especially if you maintain power during the descent.   Just keeping an eye on the EGTs during descent will let you know what's going on. 

[zehutiman]

2 hours ago, N201MKTurbo said:

Three things that can cause that (that I know of). 

1.   That cylinder is running leaner than the others.

        Do a lean test and see if that cylinder peaks at the same FF as the rest.

2.   One plug isn't firing in that cylinder.

        Do an in flight mag check and see what the EGTs are on the individual mags.

3.   The sensor is bad.

        Swap the sensors between cylinders. or at least remove and inspect the sensors.

I tried number 2. yesterday, but didn’t notice a change.  However, I wasn’t sure how long to let the engine run on each mag, so i only ran it that way for about 10 seconds — not much time for the temp to change.  How long should I run the engine on each mag?

[Marc_B]

@zehutiman Savvy has several flight profiles they recommend.  Every time I do this they always want even more time to see trends.  Short answer, at least 10 engine monitor cycles (I run mine for at least 30 seconds).

https://resources.savvyaviation.com/wp-content/uploads/savvy_pdf/SavvyAnalysisFlightTestProfiles.pdf

[Ragsf15e]

40 minutes ago, zehutiman said:

I tried number 2. yesterday, but didn’t notice a change.  However, I wasn’t sure how long to let the engine run on each mag, so i only ran it that way for about 10 seconds — not much time for the temp to change.  How long should I run the engine on each mag?

It will change quickly.  If a plug wasn’t firing you’d also feel roughness.  It would likely be pretty obvious.  Try #1, maybe you have a partially clogged injector.

[N201MKTurbo]

1 hour ago, zehutiman said:

I tried number 2. yesterday, but didn’t notice a change.  However, I wasn’t sure how long to let the engine run on each mag, so i only ran it that way for about 10 seconds — not much time for the temp to change.  How long should I run the engine on each mag?

In the event of a mag failure the engine is expected to run on one mag till the tanks are dry.

But if a plug wasn't firing, you would have felt it.

[zehutiman]

7 hours ago, Marc_B said:

@zehutiman Savvy has several flight profiles they recommend.  Every time I do this they always want even more time to see trends.  Short answer, at least 10 engine monitor cycles (I run mine for at least 30 seconds).

https://resources.savvyaviation.com/wp-content/uploads/savvy_pdf/SavvyAnalysisFlightTestProfiles.pdf

I’ll try that tomorrow.

[jlunseth]

Just asking to verify. Is this behavior a change from past observed temps, or is it possible it has always been going on and you just noticed it?

[zehutiman]

On 10/21/2023 at 9:18 AM, jlunseth said:

Just asking to verify. Is this behavior a change from past observed temps, or is it possible it has always been going on and you just noticed it?

No, it’s definitely new behavior.

[Shadrach]

I’m thinking it’s a sensor issue given the mags checked out in flight mag. Your engine has a CR of 8.5:1.  1573° is outside of the norm for which an engine unless there is an ignition problem. Would have been interesting to know the single mag EGT on the cylinder. I expect the reading was in excess of 1700° Would be highly suspect. You could try swapping probes, but removing exhaust probes can sometimes damage them. . I would replace the probe. It’s a low risk investment, and the most likely cause of the issue.

[Ragsf15e]

41 minutes ago, Shadrach said:

I’m thinking it’s a sensor issue given the mags checked out in flight mag. Your engine has a CR of 8.5:1.  1573° is outside of the norm for which an engine unless there is an ignition problem. Would have been interesting to know the single mag EGT on the cylinder. I expect the reading was in excess of 1700° Would be highly suspect. You could try swapping probes, but removing exhaust probes can sometimes damage them. . I would replace the probe. It’s a low risk investment, and the most likely cause of the issue.

I sometimes see egts that high after descending from lop cruise.  Say cruising at 10,000’, nose down, don’t touch anything else.  Egts start to climb slowly during decent.  Maybe around 4 or 5,000’ they set off the yellow “caution” on my jpi930 as they pass 1500.  I guess I’m saying maybe those egts could be possible at lower altitude near peak? I don’t think egt probes usually fail this way, but I agree it’s worth checking?

[Shadrach]

On 10/31/2023 at 10:49 PM, Ragsf15e said:

I sometimes see egts that high after descending from lop cruise.  Say cruising at 10,000’, nose down, don’t touch anything else.  Egts start to climb slowly during decent.  Maybe around 4 or 5,000’ they set off the yellow “caution” on my jpi930 as they pass 1500.  I guess I’m saying maybe those egts could be possible at lower altitude near peak? I don’t think egt probes usually fail this way, but I agree it’s worth checking?

He’s at 1573 in cruise. I do have one cylinder that will just break 1500° at low altitude at WOTRAO.   1573° at 21.5”x2520 seems unlikely.

[PT20J]

Easy to swap probes and see if the problem stays with the cylinder or follows the probe.

[EarthboundMisfit]

Are you running ROP or LOP in those photos? 

For comparison our IO-550G in cruise (9000ft, approx 20 deg LOP) last week:

[Shadrach]

15 hours ago, PT20J said:

Easy to swap probes and see if the problem stays with the cylinder or follows the probe.

On more than one occasion, I’ve had exhaust probes get flakey after being disturbed. I don’t know why exactly. I’d guess that they were marginal before removal and the process finished them off. It’s good idea to have a spare or two on hand just in case.