High climb CHT on cylinder #4

[Shadrach]

1967 F with stock cowl. This setup has traditionally been very cool with #1 and #4 being the coolest cylinders in both climb and cruise. For #1 and #4, Climb temps are usually <335° even at Vy and <300° in cruise.  In the winter I except cruise CHTs in the mid 280° to low 290° range.

Several weeks ago on a local flight I noticed #1 was pushing 340° and #4 was above 360° before reaching pattern altitude. I thought perhaps it was the warm OAT so I dropped the nose for cruise climb of 130mph. Passing through 5k I was struggling to keep #4 under 370°. I returned to base immediately thinking maybe the baffle seal was flipped in the wrong direction.

On the ground, I determined that everything was installed as it should be. I second-guessed myself and departed again. Once again, I aborted the flight due to climb temps and returned to base.

After decowling the airplane I found that an oily piece of Scotch-Brite pad had been ingested into the cowl and had wedged between the #4 cylinder barrel and the rear baffle wall. 

I took off again and found #1 was back to normal (odd) but #4 was still running hotter than normal in cruise climb but less so 355-360. In cruise it settles down into the 320s.

#4 EGT is in the mid to low 1200s which is higher than I’d like but should be rich enough and is close to where it’s always been. We verified the injector was clean but soaked it in Hoppes for 10 mins just to be sure.

All internal baffle seals are installed as they should be and everything looks normal.

Subsequent flights continue to produce higher than normal climb cht on #4.

I know that none of these temperatures are concerning. However, something has changed and I don’t like that.  I have always appreciated that I was able to conduct sustained, maximum performance climbs without worry of overheating. A luxury that I do not have under the current circumstances.

Does anyone have any idea about what might be cause high climb CHT on a single cylinder? I’m at a loss.

[Echo]

I do not, but I am looking forward to seeing what resulted in the outcome. Good catch on the scotch-brite pad!

[Andy95W]

Induction leak?

[Shadrach]

14 minutes ago, Echo said:

I do not, but I am looking forward to seeing what resulted in the outcome. Good catch on the scotch-brite pad!

If I did not have an engine monitor, it would likely still be there

[PT20J]

Hmmm. Let’s see.

1. This is an airplane you have been flying for many years and know well.

2. #1 and #4 traditionally have the coolest climb CHTs

3. Suddenly, and for no apparent reason, #1 and #4 CHTs got significantly hotter.

4. You investigated and removed a small obstruction from the cooling fins of #4.

5. On a subsequent flight, #1 was cooler but #4 was still running hot.

The symptoms don’t make sense, which is why you posted. Just a guess, but I’d assume that the scotchbrite was a red herring and look into perhaps an issue with the engine monitor. 

[takair]

Ross…might take a look at the bottom of the cylinder near the thermocouple.  Would look at things like exhaust leak, the inter cylinder baffle on the bottom between cylinders, and the wire/springs that pull the front and rear baffles together.  Broken wire might allow the baffles to not wrap around bottom of the jug.  Flow in climb may just be different enough to cause issue in climb and not cruise.

Edited July 5 by takair
Changed wording to match described symptom

[Shadrach]

1 hour ago, PT20J said:

Hmmm. Let’s see.

1. This is an airplane you have been flying for many years and know well.

2. #1 and #4 traditionally have the coolest climb CHTs

3. Suddenly, and for no apparent reason, #1 and #4 CHTs got significantly hotter.

4. You investigated and removed a small obstruction from the cooling fins of #4.

5. On a subsequent flight, #1 was cooler but #4 was still running hot.

The symptoms don’t make sense, which is why you posted. Just a guess, but I’d assume that the scotchbrite was a red herring and look into perhaps an issue with the engine monitor. 

That is a reasoned response. I installed a new JPI in between flights so it’s not the box.  I will investigate further.

[PT20J]

2 minutes ago, Shadrach said:

That is a reasoned response. I installed a new JPI in between flights so it’s not the box.  I will investigate further.

Let us know. It’s a puzzler. 

[AndreiC]

Have you confirmed that what is listed as #1, #2, etc on your monitor corresponds to the actual cylinder numbers? I had an issue at some point suggesting that the #2 EGT sensor had failed, when in fact what had happened was that the #1 sensor had just come out of the mounting spot, but the wires were connected funny. Upon further inspection it turned out that the EGT sensors for 1, 2, 3, 4 correspond to display numbers 2, 4, 3, 1! No idea how 3 of them got switched. 
 

Reason I am suggesting to look at this is that if the CHT’s for 1 and 4 got switched around, that would explain why the improvement did not happen on 4 but on 1 instead. 

[Shadrach]

12 minutes ago, AndreiC said:

Have you confirmed that what is listed as #1, #2, etc on your monitor corresponds to the actual cylinder numbers? I had an issue at some point suggesting that the #2 EGT sensor had failed, when in fact what had happened was that the #1 sensor had just come out of the mounting spot, but the wires were connected funny. Upon further inspection it turned out that the EGT sensors for 1, 2, 3, 4 correspond to display numbers 2, 4, 3, 1! No idea how 3 of them got switched. 
 

Reason I am suggesting to look at this is that if the CHT’s for 1 and 4 got switched around, that would explain why the improvement did not happen on 4 but on 1 instead. 

I have, but even if they were, the high cht is definitely new regardless of whether the cylinder numbers are incorrect. Although it might explain why removing debris from #3 resulted caused #1 to return to normal. I’ll double check the next time I’m at the drome

[AndreiC]

I was just suggesting to look closer to the *other* cylinder whose temps have gone higher earlier. If the wires got swapped, and somehow whatever was ingested blocked the airflow on two cylinders, clearing one would have shown as improving the other one.  

[tony]

I found if I made a small space between the baffle and the back of cylinder number 4, it dropped the CHT significantly.  I just used a washer to create the gap.  Using all that high temp silicone to seal it all up just made it worse.  

Edited July 5 by tony

[Shadrach]

37 minutes ago, tony said:

I found if I made a small space between the baffle and the back of cylinder number 4, it dropped the CHT significantly.  I just used a washer to create the gap.  Using all that high temp silicone to seal it all up just made it worse.  

I did that on #3 where the barrel doesn’t have fins.

[PT20J]

11 hours ago, Shadrach said:

I have, but even if they were, the high cht is definitely new regardless of whether the cylinder numbers are incorrect. Although it might explain why removing debris from #3 resulted caused #1 to return to normal. I’ll double check the next time I’m at the drome

Ross, easiest way to do this is to aim a heat gun at each cylinder near the probe and see which rises on the monitor.

BTW, are you using bayonet probes or spark plug gasket probes?

[Shadrach]

Bayonet. I was planning on using a hairdryer.

My partner has the plane right now. The most plausible explanation is that the exhaust stack is leaking and blowing hot gases around the other side of the cylinder. However, the fact that it’s only manifesting in climb is the head scratcher. Cruise CHT in the typical 300-315° range. The issue is only manifesting itself in climb. I don’t think we could climb at Vy and keep #4 CHT under 400°. VX is out of the question. prior to this issue I could climb with the gear down and full flaps at 80 miles an hour and keep it below 350° now it’s at 350° before lift off. The only thing I can think of is that in Cruise, there’s enough airflow to redirect the exhaust leak away from the thermocouple. I’ll know more when I can put eyes on the engine. It’s only been doing this for a few hours, so probably not a lot of exhaust residue to act as a witness mark

[PT20J]

42 minutes ago, Shadrach said:

Bayonet. I was planning on using a hairdryer.

My partner has the plane right now. The most plausible explanation is that the exhaust stack is leaking and blowing hot gases around the other side of the cylinder. However, the fact that it’s only manifesting in climb is the head scratcher. Cruise CHT in the typical 300-315° range. The issue is only manifesting itself in climb. I don’t think we could climb at Vy and keep #4 CHT under 400°. VX is out of the question. prior to this issue I could climb with the gear down and full flaps at 80 miles an hour and keep it below 350° now it’s at 350° before lift off. The only thing I can think of is that in Cruise, there’s enough airflow to redirect the exhaust leak away from the thermocouple. I’ll know more when I can put eyes on the engine. It’s only been doing this for a few hours, so probably not a lot of exhaust residue to act as a witness mark

That makes sense. Cooling airflow is different in climb: more volume, but less pressure differential I would think. Also, exhaust back pressure decreases at higher altitudes.

I would try pressure testing the exhaust with a clean shop vac and a spray bottle of soapy water. 

[M20F]

My cylinder temps parallel yours.  How hot is OAT?  I am solo with 50 gallons and I have to climb at 130+ to keep #2 around 375-380 down here in ATL these days  

KBWI looks hotter than here?

[Andy95W]

Exhaust leak also explains why the temp is 350° even before takeoff, with practically no airflow.  Good luck, Ross.

[Shadrach]

3 hours ago, M20F said:

My cylinder temps parallel yours.  How hot is OAT?  I am solo with 50 gallons and I have to climb at 130+ to keep #2 around 375-380 down here in ATL these days  

KBWI looks hotter than here?

OAT is in the 80s. While these temps are not in the range of what is considered concerning. I know that something has changed #1 and #4 have traditionally been my coolest cylinders. #4 is now the hottest.

[Shadrach]

On 7/6/2024 at 12:00 PM, PT20J said:

That makes sense. Cooling airflow is different in climb: more volume, but less pressure differential I would think. Also, exhaust back pressure decreases at higher altitudes.

I would try pressure testing the exhaust with a clean shop vac and a spray bottle of soapy water. 

I found the issue. The slip joint on the #3 stack is obviously leaking. My partner put nine hours on the airplane and there is now exhaust staining on the exhaust stack and the fire sleeve of the fuel supply line going to the servo. The lower slip joint was not fully recessed in the muffler. This caused the upper slip join to be angled out slightly creating a gap. The lower slip joint was just slightly hung up in the non-recessed position. I was able to easily push it into place and square everything up. This most certainly happened post annual after lubing all of the joints with mouse milk. In the past, I have used anti-seize to lubricate the slip joints. The stack moves freely in the slip joints when the engine is cold. My question surrounds the U shaped clamp on the upper number slip joint. I’ve never really understood its purpose. I always thought it was there to Add structural integrity to the outer sleeve. I haven’t poured through the maintenance manual yet for guidance. It would be helpful if you or anyone else has some advice. I asked the local IA And he thought the clamp was there to hold the joint in place. That seems unlikely to me as the pipe is not slotted, and therefore Not really compressible.

muffler is the rib type similar to the one on the J I believe.

[PT20J]

8 minutes ago, Shadrach said:

I found the issue. The slip joint on the #3 stack is obviously leaking. My partner put nine hours on the airplane and there is now exhaust staining on the exhaust stack and the fire sleeve of the fuel supply line going to the servo. The lower slip joint was not fully recessed in the muffler. This caused the upper slip join to be angled out slightly creating a gap. The lower slip joint was just slightly hung up in the non-recessed position. I was able to easily push it into place and square everything up. This most certainly happened post annual after lubing all of the joints with mouse milk. In the past, I have used anti-seize to lubricate the slip joints. The stack moves freely in the slip joints when the engine is cold. My question surrounds the U shaped clamp on the upper number slip joint. I’ve never really understood its purpose. I always thought it was there to Add structural integrity to the outer sleeve. I haven’t poured through the maintenance manual yet for guidance. It would be helpful if you or anyone else has some advice. I asked the local IA And he thought the clamp was there to hold the joint in place. That seems unlikely to me as the pipe is not slotted, and therefore Not really compressible.

muffler is the rib type similar to the one on the J I believe.

 

 

Ross, I'm pretty sure that is a clamp to hold the two pieces of pipe together. It looks just like a common saddle clamp used to connect parts of auto exhausts. There should only need to be one slip joint per exhaust pipe. On my airplane, the clamp is tight and that joint doesn't move. It sounds like yours is just loose. 

I don't think the Mouse Milk lasts past the first heat cycle. I've started using the McFarlane DAM exhaust lube because it will wick in without taking things apart.

[Shadrach]

22 minutes ago, PT20J said:

Ross, I'm pretty sure that is a clamp to hold the two pieces of pipe together. It looks just like a common saddle clamp used to connect parts of auto exhausts. There should only need to be one slip joint per exhaust pipe. On my airplane, the clamp is tight and that joint doesn't move. It sounds like yours is just loose. 

I don't think the Mouse Milk lasts past the first heat cycle. I've started using the McFarlane DAM exhaust lube because it will wick in without taking things apart.

This is where my limited understanding of metallurgy comes into play. How does one reduce the diameter of a steel pipe with a saddle clamp? I’ve used exhaust clamps in a number of automotive applications, but in those situations, the outer pipe is notched to allow the outer pipe compress around the inner pipe. The outer pipe is not notched in this application. It seems to me the threads on the clamp would strip before the pipe compressed in any significant way. Perhaps the clamp. is designed to deform the outer pipe?

FYI, while that clamp might look like a standard automotive part, it retails for about $300.

Grateful to have an extra one on the shelf.

[EricJ]

15 minutes ago, Shadrach said:

This is where my limited understanding of metallurgy comes into play. How does one reduce the diameter of a steel pipe with a saddle clamp? I’ve used exhaust clamps in a number of automotive applications, but in those situations, the outer pipe is notched to allow the outer pipe compress around the inner pipe. The outer pipe is not notched in this application. It seems to me the threads on the clamp would strip before the pipe compressed in any significant way. Perhaps the clamp. is designed to deform the outer pipe?

The other thing that happens with exhausts is that they expand under use.   The saddle clamp will restrict expansion when the exhaust heats during use and provide a more positive seal.   I don't know the rationale for why that particular clamp is on there, but they don't have to be super tight to provide some mechanical stability even when the system is cold.  The clamp can shrink the tube a bit even without slotting.

I was going to say that the little bit of exhaust soot on the firesleeve may have happened just during startup until the system got hot.   You might try cleaning those stains up and see whether they come back or not.     All of my exhaust slip joints leak until the pipes get hot, which is not unusual.

[Shadrach]

11 minutes ago, EricJ said:

The other thing that happens with exhausts is that they expand under use.   The saddle clamp will restrict expansion when the exhaust heats during use and provide a more positive seal.   I don't know the rationale for why that particular clamp is on there, but they don't have to be super tight to provide some mechanical stability even when the system is cold.  The clamp can shrink the tube a bit even without slotting.

I was going to say that the little bit of exhaust soot on the firesleeve may have happened just during startup until the system got hot.   You might try cleaning those stains up and see whether they come back or not.     All of my exhaust slip joints leak until the pipes get hot, which is not unusual.

My slip joints also exhibit a bit of staining from leakage but the the stains on the fire sleeve are new.  I am going to clean everything thoroughly. Exhaust stains are more tenacious on bare metal than on the painted belly skins. 

I am going to try to find some factory guidance on the clamp position and torque.  Stripping the threads would be an expensive mistake.

[Fly Boomer]

50 minutes ago, PT20J said:

McFarlane DAM exhaust lube

+1