Cylinder Temperature Issue

[Brandontwalker]

I was flying on a 2.5 hour cross country a few weeks back (before the apocalypse) and, seeing that it was a CAVU day and I was cleared direct to destination immediately after contacting departure, I had plenty of time to pay close attention to the gauges.  I noticed an anomaly in cylinder 3 in that the temperature would rapidly rise 25-30 degrees hotter than normal, stay there fore a few minutes, and then cool back to normal.  It did this for four or five waves during the flight.  My senses were heightened due to the issue and it appeared to be accompanied by a very slight roughness and change in sound.  However, I cannot confirm this to be true as the roughness could have just been a false perception based on what I was seeing on the gauges.  During the flight, I performed a couple of mag checks and all was normal.  EGT's were also all normal and showed no signs of change during the the temperature events.  I have done all I can do to diagnose the issue.  The fuel injector sleeve was clear of debris.  Spark plugs were removed and looked normal.  No visible signs of exhaust or intake leaks.  Baffling looks perfect.  I am guessing the next step is for me to take it to the shop for a compression check.  Has anyone experienced this, or a similar, issue before?  Suggestions as to the cause?

[jaylw314]

Hard to imagine a compression check will tell you anything.  If your EGT isn't changing, it also seems unlikely to be a fuel or ignition problem.  That CHT is fluctuating up and down pretty fast, it seems possible it's a sensor problem--do you have a piggyback probe or spark plug gasket probe?  It's possible you're having intermittent light detonation, borescoping the cylinder should show signs of that pretty easily.  That seems unlikely in an IO-360.  I'm sure others will chime in with better ideas...

[Brandontwalker]

I forgot to mention that one of my first suspicions was a failing CHT probe.  I swapped the probes for cylinders 1 and 3.  The problem stayed with cylinder 3, so, unfortunately, not a probe problem...

[Austintatious]

another for a bad sensor... my number 6 is doing that too, but more drastic.  I suspect a connection issue though as it is a new sensor.

[Brandontwalker]

9 minutes ago, Austintatious said:

another for a bad sensor... my number 6 is doing that too, but more drastic.  I suspect a connection issue though as it is a new sensor.

I guess I could wire the #3 probe to #1 readout on the EDM to rule out a problem with the wiring to the EDM.

[EricJ]

Can you download the engine data from your monitor?    It could be an aliased representation of a burned exhaust valve.    A borescope inspection would be informative.

[kmyfm20s]

I know you said you checked for exhaust leaks but I would take a harder look around the exhaust gasket and flange. This happened to me and it only takes a small steam of exhaust gases to hit the probe area to do this. 

[M20S Driver]

15 minutes ago, kmyfm20s said:

I know you said you checked for exhaust leaks but I would take a harder look around the exhaust gasket and flange. This happened to me and it only takes a small steam of exhaust gases to hit the probe area to do this. 

Agreed.  I had a post on my case.  We could not see any evidence of exhaust leak initially since it was so minor.

[Brandontwalker]

9 minutes ago, M20S Driver said:

Agreed.  I had a post on my case.  We could not see any evidence of exhaust leak since it was so minor.

I will check the gasket.  A $10 fix would be the cheapest outcome possible.

[M20S Driver]

6 minutes ago, Brandontwalker said:

I will check the gasket.  A $10 fix would be the cheapest outcome possible.

I would check the torque first.  That was all my mechanic had to do

[carusoam]

1) What is causing the big red X with the JPI fuel level? Related/unrelated...  (new installation?) 

2) data swinging visually is great...  takes more memory than I have to do anything with...

2.1) EGT and CHT both seem to be swinging for that same cylinder...   most likely, not an individual sensor issue...

3) Next steps... download data off the JPI... Upload data to Savvy... enable sharing....

4) Copy link from Savvy to here...

5) this technique allows visualization of scads of data and shows interactions very easily...
 

6) exhaust leaks have a tendency to do things like this... do you have a CO monitor? Any unusual CO levels to report?

 

PP thoughts only, not a mechanic...

Best regards,

-a-

 

[jlunseth]

Well, I noticed that the EGT is actually changing.  It is not a big change relative to EGT total temp.  The EGT appears to roll down from around 1312 to somewhere in the 1290's. The CHT increase lags behind that, which makes sense because the metal of the cylinder needs to warm up for the change to show on the CHT probe.  Then the EGT falls again, and the CHT does also but lagging the EGT.  Since it is showing up on one cylinder, wouldn't an injector clog of some kind be likely, something that is moving or flipping around inside the injector, making the fuel flow lean out, then go back to rich, etc.?

Edited April 10, 2020 by jlunseth

[jlunseth]

Also, it is worth noting that EGT is not an actual temperature, but more of an average of the very rapid up and down puffs of temp that come out of the exhaust valve every time it opens and closes.  It is a measure of the temperature to which the EGT probe is heated by those puffs of exhaust gas, not the temp of the gas itself.  So the actual gas temp rise and fall may actually be more than what is showing on the read-out, because the probe lags the gas temp.

Could be something in the spider also, that is giving cylinder 3 and uneven flow of fuel.

[Brandontwalker]

1 hour ago, jlunseth said:

Also, it is worth noting that EGT is not an actual temperature, but more of an average of the very rapid up and down puffs of temp that come out of the exhaust valve every time it opens and closes.  It is a measure of the temperature to which the EGT probe is heated by those puffs of exhaust gas, not the temp of the gas itself.  So the actual gas temp rise and fall may actually be more than what is showing on the read-out, because the probe lags the gas temp.

Could be something in the spider also, that is giving cylinder 3 and uneven flow of fuel.

I checked the injector and it is good. However, I have not checked the spider. Will leave that task to my mechanic if needed. Thanks for the suggestions.  

[Ragsf15e]

Based on the thermal mass of cylinders, they generally can’t change temperature really quickly like the egt can. Saavy could probably tell you right away if it’s possibly real data or likely not.  

If we assumed that the cylinder didn’t actually heat up that quickly, the exhaust leak theory seems pretty plausible because it has the potential to change both cht and egt readings by blowing out some of the hot egt onto the cht probe.

[Guest]

Have you checked the instrument ground wire, the engine to airframe ground cable and the probe wiring?

Clarence

[Oscar Avalle]

Just saw a new post about carburetors, fuel flow and CHT you may want to have a look at it


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[larrynimmo]

Keep in mind that valves are designed to rotate and this could be an indication of an exhaust valve that is not sealing right half the time....mike bush from saavy teaches just this type of failure....send your monitor data and he will tell you what’s going on

[Warren]

Savvy has an article (mentioned by larrynimmo above) on predicting exhaust valve failure.  One of the predictors is a cyclic EGT.  If there is a bad spot on the valve and the seat, the valve rotator will rotate the valve to line up approx. every 1 min and create a higher EGT.  Search their site and read the article.  It is relatively easy to diagnose with a borescope and generally an educational and interesting article.

[Brandontwalker]

It has been a few weeks of testing and implementing your suggestions, all of which I appreciate. After many blanks, I took the plane to my IA on Saturday. He pulled the prop through by hand and advised compression is very low on the problematic cylinder. He requested that I order a new jug and piston (wrist pin, rings, assembly, etc...) from J&J Air Parts. He said to plan for around $1,400 in parts plus 2-3 days of labor for replacement. What are your thoughts regarding the fix and time budget? For reference, this is a 1350 hour engine.


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[gsxrpilot]

16 minutes ago, Brandontwalker said:

He pulled the prop through by hand and advised compression is very low on the problematic cylinder. He requested that I order a new jug and piston

I"m sure you've left out a lot of the details. But that statement sounds like a doctor putting his hand on your forehead and then saying, "yes, I think you need heart surgery."

Did he actually do a compression check? If so, what was the compression on that cylinder? Did he borescope to look at the valves? 

Maybe I missed this part of the conversation. But I would be hesitant to swap a cylinder out based on the feel of pulling the prop through by hand.

[StevenL757]

41 minutes ago, Brandontwalker said:

It has been a few weeks of testing and implementing your suggestions, all of which I appreciate. After many blanks, I took the plane to my IA on Saturday. He pulled the prop through by hand and advised compression is very low on the problematic cylinder. He requested that I order a new jug and piston (wrist pin, rings, assembly, etc...) from J&J Air Parts. He said to plan for around $1,400 in parts plus 2-3 days of labor for replacement. What are your thoughts regarding the fix and time budget? For reference, this is a 1350 hour engine.

 

18 minutes ago, gsxrpilot said:

I"m sure you've left out a lot of the details. But that statement sounds like a doctor putting his hand on your forehead and then saying, "yes, I think you need heart surgery."

Did he actually do a compression check? If so, what was the compression on that cylinder? Did he borescope to look at the valves? 

Maybe I missed this part of the conversation. But I would be hesitant to swap a cylinder out based on the feel of pulling the prop through by hand.

What @gsxrpilot said.

Sidebar questions...probably unrelated, but...

• How much oil are going through?  1 quart every_________hours?
• How often are you doing oil changes?  Every _______ hours?

Steve

[Brandontwalker]

21 minutes ago, gsxrpilot said:

I"m sure you've left out a lot of the details. But that statement sounds like a doctor putting his hand on your forehead and then saying, "yes, I think you need heart surgery."

Did he actually do a compression check? If so, what was the compression on that cylinder? Did he borescope to look at the valves? 

Maybe I missed this part of the conversation. But I would be hesitant to swap a cylinder out based on the feel of pulling the prop through by hand.

No details omitted. Yes, that is part of my hesitation. The other part of hesitation comes from the fact that he indicated the opposing cylinder also needs to be removed to ensure proper torquing of the bolts. I am admittedly uneducated on the subject, but the through case bolts seem to be accessible without removing the opposing cylinder. I am worried about opening more than necessary due to greater risk of maintenance induced failure. 

[Brandontwalker]

1 minute ago, StevenL757 said:

 

What @gsxrpilot said.

Sidebar questions...probably unrelated, but...

• How much oil are going through?  1 quart every_________hours?
• How often are you doing oil changes?  Every _______ hours?

Steve

Oil consumption is up and I am seeing oil from the breather. This seems to confirm a compression issue. Before, I was seeing 11 hours per quart. Now I am at 6-7 hours per quart. Oil changes have routinely been at, or before, 50 hours.

[skykrawler]

Get a second opinion.  Don't tell them what the first person said.