Overheating Cylinder

Cpt_Kirk

Cpt_Kirk

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Ted Striker
I have a #6 on a big bore Lycoming that's at least 40 degrees hotter than the next hottest cylinder. I have to run extremely rich to keep it under 400f in the climb and in cruise. EGTs are normal are inline with the other 5 cylinders.

What would be your first steps in diagnosing something like this as a pilot? Ive stopped flying it until its resolved.

What are some common causes for a single overheating cylinder?
 
Look at your baffling. Sometimes the airflow around the back side of aft cylinders is completely blocked by baffling. You need airflow around the fins on the aft side of that cylinder.

Otherwise, perhaps you have an induction leak on that one or something is restricting fuel flow if you're injected.
 
I assume you have verified the baffling is in place and does not spring out due to air pressure. You can figure 112 mph equals one foot of water head and rising/falling by the square of the airspeed to get an idea of the baffle forces involved. It is necessary that air flow thru the fins and not just around the fins.

Consider any apparent restrictions to airflow thru the head or cylinder fins. It could be general contamination due to oil plus dust etc.

I have seen a poorly matched head casting in which the fins were offset slightly when the head casting mold pattern was assembled at the foundry creating air-blocking flash where they come together. There was an obvious air blockage where the foundry cores came together - and it was even obvious on a cylinder assembly at a cylinder manufacturer's display at Oshkosh! No fix of course except to replace with a good cylinder.
 
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Did it just start doing this, or has it always run hotter than the others.

My Nr 6's in the Baron run hotter than the others largely due to the fact that the oil cooler happens to be located right in front of the cylinder so it doesn't get as good of airflow as the others.
 
Swapping probes and checking the baffling were two things that immediately came to my mind. I just wasn't sure if there were other obvious issues that could cause something like this.

It just started happening. Before the annual, everything ran smoothly, within limits, and with an even spread. No specific work was done on #6.

I posted pictures of this particular engine not too long ago. The baffling was some of the best that I've seen on an airplane and other than getting caught up on the cowling when installed, I don't see it being an issue.
 
Fearless Tower said:
My Nr 6's in the Baron run hotter than the others largely due to the fact that the oil cooler happens to be located right in front of the cylinder so it doesn't get as good of airflow as the others.
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Isn't the oil cooler in front of #5?

Also, I can't tell if you're suggesting that that the OP has the same problem or not but I'd just like to point out that Lycoming numbers their cylinders differently than Continental. :)
 
mondtster said:
Isn't the oil cooler in front of #5?

Also, I can't tell if you're suggesting that that the OP has the same problem or not but I'd just like to point out that Lycoming numbers their cylinders differently than Continental. :)
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Speaking of which, isn't #6 on a Lycoming the right rear as looking from the pilot's seat?
 
mondtster said:
Isn't the oil cooler in front of #5?

Also, I can't tell if you're suggesting that that the OP has the same problem or not but I'd just like to point out that Lycoming numbers their cylinders differently than Continental. :)
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I don't fly Lycs. Just throwing it out as an idea.

As far as NR5 or NR6, I'd have to look. It is possible my probes on the JPI are wired to the wrong cylinders.
 
Cpt_Kirk said:
Swapping probes and checking the baffling were two things that immediately came to my mind. I just wasn't sure if there were other obvious issues that could cause something like this.

It just started happening. Before the annual, everything ran smoothly, within limits, and with an even spread. No specific work was done on #6.

I posted pictures of this particular engine not too long ago. The baffling was some of the best that I've seen on an airplane and other than getting caught up on the cowling when installed, I don't see it being an issue.
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I'd start with checking that probe. Might have been disturbed and is giving a bum reading.
 
If it isn't the probe or the baffling.....you're probably looking at a broken compression ring, clogged fuel injector, bad plug.....ignition lead, or magneto...

Next step....get yourself a one of those cheap USB dental cameras....and have a look at the cylinder walls and see if it's scored. If so, then you're looking at a new cylinder and piston in your future....or those other items listed above.:goofy:

a lean mag check at altitude at 65% power will show the ignition/plug/mag issue for that cylinder.
 
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Cpt_Kirk said:
Speaking of which, isn't #6 on a Lycoming the right rear as looking from the pilot's seat?
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I didn't know this until now, but it looks like some Lycomings may be configured as you're describing, and I believe you might have one set up this way. All the 540s I've worked on however have #5 in the right rear. I thought they were all that way. See the attached picture.
 

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mondtster said:
I didn't know this until now, but it looks like some Lycomings may be configured as you're describing, and I believe you might have one set up this way. All the 540s I've worked on however have #5 in the right rear. I thought they were all that way. See the attached picture.
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I saved that picture. Thanks.
 
Cpt_Kirk said:
I have a #6 on a big bore Lycoming that's at least 40 degrees hotter than the next hottest cylinder. I have to run extremely rich to keep it under 400f in the climb and in cruise. EGTs are normal are inline with the other 5 cylinders.

What would be your first steps in diagnosing something like this as a pilot? Ive stopped flying it until its resolved.

What are some common causes for a single overheating cylinder?
Click to expand...

Injected?
 
Ted, since you're looking for any info... Check the #6 bottom plug for tightness, and the #4 and #6 exhaust risers for tightness. If hot exhaust is hitting the CHT probe, it could cause a bad indication, even if you swap probes with another cylinder (but you should see soot).
 
Tom-D said:
Are they in the right hole?

Is this a sudden change?

When were they last cleaned?
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I'd assume so, but I don't know.

Yes.

It may have been done during the annual, but I'm not sure. It's been out of the annual a little over a week.
 
Cpt_Kirk said:
I'd assume so, but I don't know.

Look at each one, they have a number on them. #1 should be in #1 cylinder and so on.

Yes.

Ask what your annual inspector did to the nozzles

It may have been done during the annual, but I'm not sure. It's been out of the annual a little over a week.
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take it back and ***** like crazy.
 
Doesn't Lycoming recommend CHT under 420 in normal ops and isn't the redline 500*? I'd want to identify why the change in temp but the temp itself isn't cause for grounding. At least from where I sit. :)
 
and another thing regarding the CHT temp limits.....the temperature is not uniform while the cylinder is operating. So, if the probe is the bayonet type and screwed into the side of the cylinder vs. the spark plug ring type....they will read 50-100 deg F different. The spark plug ring type sensor will read hotter....cause it's hotter at that location.

Any guesses why 380, 400, 420 are the values given for limits?....cause some where else on the cylinder it's getting hotter and close to material limits.
 
The initial post's reference to "big bore" threw me at first. I've never heard anyone call any Lycoming a big bore. I guess an 0-360 would qualify too? If so, what's a 390 or a 580 called? ;)
 
Stewartb said:
Doesn't Lycoming recommend CHT under 420 in normal ops and isn't the redline 500*? I'd want to identify why the change in temp but the temp itself isn't cause for grounding. At least from where I sit. :)
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I will never run my engines that hot. Run your engine hot and you're seriously degrading the strength of the metal. Run your engine that hot and you may just "shock cool" the engine when pulling the power off. Run your engine that hot and you're playing with a great chance of a thermal runway with an impending engine failure. It's most definitely a cause for grounding.

When only one fire breather is keeping me in the air, I do everything I can to take care of it.

This chart references P&W, but it should give you an idea.

pp18n.jpg


Checkout_my_Six said:
and another thing regarding the CHT temp limits.....the temperature is not uniform while the cylinder is operating. So, if the probe is the bayonet type and screwed into the side of the cylinder vs. the spark plug ring type....they will read 50-100 deg F different. The spark plug ring type sensor will read hotter....cause it's hotter at that location.

Any guesses why 380, 400, 420 are the values given for limits?....cause some where else on the cylinder it's getting hotter and close to material limits.
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I don't know which one is installed on this airplane. I'll look when I have the opportunity.

The problem is getting fixed. I just wanted to run it around on to see what everyone else thought could be the problem.
 
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If EGT's are all level it is not an induction leak or fuel delivery problem. Most likely probe or baffle seal. Sometimes they get a kink or fold the wrong way when you put the cowl on and you can't see it.
 
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