High CHT on Cessna 172

C

Cmercado

Pre-takeoff checklist
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Jan 16, 2012
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San Juan, Puerto Rico
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Charlie M
Hi guys,

I know this topic is been around forever. But I want to check a few tricks and rule out some other issues. I just installed a new JPI 730 (BTW, very nice toy....) and Cylinder # 3 is reading 455 Deg :mad2::mad2: in full power climb. The plane is a 1974 C172 M O-320

1. Rest of the cylinders are between 370 to 390 in climb
2. EGT in number 3 is about 1490-1530
3. Outside air temp is 85 Deg

Level in cruise the # 3 temp will drop to 410-415. the others around 350-360. I am replacing baffle seals on Monday. Do you guys have any experience with the exhaust fairing that is STC'd for the 172 (I think from Maple Leaf). They claim a 20 deg reduction in CHT temps. That is on schedule if the baffle seal replacement fails...

Any advice?

Charlie
 
Blanche (Murphey) found rusty cylinder walls after noting high cylinder temp on one of four. Borescope was easy way to see problem after checking baffles and probes.
 
I will check if my AP owns a boroscope. If he does we will check it on Monday, I will redo the baffle seals anyway.

Any experience with the exhaust fairing??
 
Cmercado said:
I will check if my AP owns a boroscope. If he does we will check it on Monday, I will redo the baffle seals anyway.

Any experience with the exhaust fairing??
Click to expand...

No experience with exhaust fairing at all. Not sure what is meant. Have heat shields on the exhaust system so inspect those but no fairings.

Baffle check should include seals and that all baffles are in place. I found one baffle missing from the aft baffle assembly after careful inspection (A&P IA missed it). I only found it by comparing parts manual picture with actual assembly.
 
This one. It is supposed to help cool your engine...
 

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You might look critically at each of the fin openings by looking from the top and shining a flashlight up from below (preferably in a dark room) & imagine/consider how smoothly air will pass through. I've seen a couple of cylinder heads where the original casting molds were poorly matched when the head was made creating a considerable air dam.
 
What do the plugs in that cylinder look like compared to the other cylinders?

Is that cylinder running closer to Peak than the others while at full open throttle?
 
Tom-D said:
What do the plugs in that cylinder look like compared to the other cylinders?

Is that cylinder running closer to Peak than the others while at full open throttle?
Click to expand...

Tom,

The plugs looked the same in all 4. EGTs are about the 75 deg from each other..... I really have no clue on this one...
 
Nate Duehr said it best when he said "An engine monitor will give you more information than you ever want to know."

I had the same issue in my 172 - I solved it by buying a Mooney ;) In my case, it was also cylinder #3 - it would run about the same temp (455-460) never did figure out what it was.
 
DavidWhite said:
Nate Duehr said it best when he said "An engine monitor will give you more information than you ever want to know."

I had the same issue in my 172 - I solved it by buying a Mooney ;) In my case, it was also cylinder #3 - it would run about the same temp (455-460) never did figure out what it was.
Click to expand...

Did you change baffle seals?? Boroscope?? Probably I will follow your advice... There is a very nice Trinidad for sale at my airport:rofl::rofl::rofl:
 
I have been chasing this same issue in my Cherokee, since I installed an engine monitor. I have done the borescope and had the baffles fully gone through and looked at them myself. Very frustrating. It is #3 for me as well.
 
Don't forget the inter-cylinder baffle as well, it's often overlooked.
 
John221us said:
I have been chasing this same issue in my Cherokee, since I installed an engine monitor. I have done the borescope and had the baffles fully gone through and looked at them myself. Very frustrating. It is #3 for me as well.
Click to expand...

Concensus among a number of Lycoming/Piper specialists (private emails, local shops) is that #3 is always running hotter than the others. After the borescope, re-hone all 4 cylinders & new rings, and swapping the cylinders around, the temps on mine are more reasonable, but I accept that #3 position will run warm. Because the new work happened in December, I haven't had a chance to see what summer heat will do. But in 60F weather, I'm seeing higher temps on #3 (400-420F) only during take-offs. In cruise all 4 are 340-360.
 
Cmercado said:
Did you change baffle seals?? Boroscope?? Probably I will follow your advice... There is a very nice Trinidad for sale at my airport:rofl::rofl::rofl:
Click to expand...

I changed the baffle seals to silicon ones and it didn't make a difference. Changed oil types, tried making a blood sacrifice to the engine gods, but to no avail.
 
murphey said:
Concensus among a number of Lycoming/Piper specialists (private emails, local shops) is that #3 is always running hotter than the others. After the borescope, re-hone all 4 cylinders & new rings, and swapping the cylinders around, the temps on mine are more reasonable, but I accept that #3 position will run warm. Because the new work happened in December, I haven't had a chance to see what summer heat will do. But in 60F weather, I'm seeing higher temps on #3 (400-420F) only during take-offs. In cruise all 4 are 340-360.
Click to expand...

We fly the Caribbean so we are expecting higher temps anyway. But 460 at climb really worries me....... That is why I am trying to get some info on the exhaust fairing before I bite the bullet.....
 
Cmercado said:
We fly the Caribbean so we are expecting higher temps anyway. But 460 at climb really worries me....... That is why I am trying to get some info on the exhaust fairing before I bite the bullet.....
Click to expand...
Have you verified it was an accurate reading yet?
 
One cylinder's CHT that is too hot in climb can indicate at least three kinds of problems.

1 the one to worry about is preignition and detonation, which can melt a piston and ruin the cylinder. That is why some suggested an immediate borescope, which is what I would do.

If this is what is happening to you, the CHT probe indication will climb gradually at about 1 degree F per second or even more. This rise happens over the course of about 30 sec, reaching a dangerously high level well over 400 F. It is most likely during takeoff and climbout, so this is the time to monitor CHT. This is perhaps the most urgent indication of problems that you can identify with the engine analyzer. Action to take while still airborne: Reduce power immediately, improve cooling by lowering nose (and adjusting mixture richer if ROP or leaner if LOP), and land as soon as possible. Have the cylinder borescoped.

2 If the borescope shows no problem, I would ask the mechanic to swap two probes, to see if the problem moves with the probe the next time I fly. That would indicate a faulty probe.

3 If the high CHT indication is sporadic and the CHT seems to jump up and down 50 or 100 degrees in a matter of a few seconds, that would indicate a faulty connector on a probe. I have experienced that problem, and it happened most often during climb out, when stuff in the engine compartment is most stressed, mechanically. This situation (high CHT in one cylinder during climb) could cause one to wrongly suspect preignition. The giveaway that it's an unrealistic rapid CHT change, much faster than 1 deg F per sec -- the metal in a cylinder can't actually heat that fast.

Mike Busch webinar here: http://www.eaavideo.org/video.aspx?v=1778564324001
 
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murphey said:
Concensus among a number of Lycoming/Piper specialists (private emails, local shops) is that #3 is always running hotter than the others. After the borescope, re-hone all 4 cylinders & new rings, and swapping the cylinders around, the temps on mine are more reasonable, but I accept that #3 position will run warm. Because the new work happened in December, I haven't had a chance to see what summer heat will do. But in 60F weather, I'm seeing higher temps on #3 (400-420F) only during take-offs. In cruise all 4 are 340-360.
Click to expand...

I can keep it under 420 if I baby it after initial climb (pattern altitude) and can keep it under 400 (barely) in cruise as long as I pull back a bit. It just doesn't seem right. If I don't baby it, it will climb close to 450 on #3. I am going to calibrate the probes next, but they are brand new.
 
NoHeat said:
One cylinder's CHT that is too hot in climb can indicate at least three kinds of problems.

1 the one to worry about is preignition and detonation, which can melt a piston and ruin the cylinder. That is why some suggested an immediate borescope, which is what I would do.

If this is what is happening to you, the CHT probe indication will climb gradually at about 1 degree F per second or even more. This rise happens over the course of about 30 sec, reaching a dangerously high level well over 400 F. It is most likely during takeoff and climbout, so this is the time to monitor CHT. This is perhaps the most urgent indication of problems that you can identify with the engine analyzer. Action to take while still airborne: Reduce power immediately, improve cooling by lowering nose (and adjusting mixture richer if ROP or leaner if LOP), and land as soon as possible. Have the cylinder borescoped.


Mike Busch webinar here: http://www.eaavideo.org/video.aspx?v=1778564324001
Click to expand...
That is exactly what is happening to my Cessna.
 
Cmercado, can you download from your monitor to a flash drive and then upload to savvy analysis?

That will make a timeline graph that will allow you to really see what is happening best.

Is you post a screenshot of the graph, you might get some better interpretation here.
 
NoHeat said:
One cylinder's CHT that is too hot in climb can indicate at least three kinds of problems.

1 the one to worry about is preignition and detonation, which can melt a piston and ruin the cylinder. That is why some suggested an immediate borescope, which is what I would do.

If this is what is happening to you, the CHT probe indication will climb gradually at about 1 degree F per second or even more. This rise happens over the course of about 30 sec, reaching a dangerously high level well over 400 F. It is most likely during takeoff and climbout, so this is the time to monitor CHT. This is perhaps the most urgent indication of problems that you can identify with the engine analyzer. Action to take while still airborne: Reduce power immediately, improve cooling by lowering nose (and adjusting mixture richer if ROP or leaner if LOP), and land as soon as possible. Have the cylinder borescoped.

2 If the borescope shows no problem, I would ask the mechanic to swap two probes, to see if the problem moves with the probe the next time I fly. That would indicate a faulty probe.

3 If the high CHT indication is sporadic and the CHT seems to jump up and down 50 or 100 degrees in a matter of a few seconds, that would indicate a faulty connector on a probe. I have experienced that problem, and it happened most often during climb out, when stuff in the engine compartment is most stressed, mechanically. This situation (high CHT in one cylinder during climb) could cause one to wrongly suspect preignition. The giveaway that it's an unrealistic rapid CHT change, much faster than 1 deg F per sec -- the metal in a cylinder can't actually heat that fast.

Mike Busch webinar here: http://www.eaavideo.org/video.aspx?v=1778564324001
Click to expand...

Swap probes first - fastest, easiest & cheapest.

Next - Mike B has great information but remember most of his articles and research relates to his fuel-injected, big HP engines, not the little carb O-360/320 in the cherokees.
 
NoHeat said:
Cmercado, can you download from your monitor to a flash drive and then upload to savvy analysis?

That will make a timeline graph that will allow you to really see what is happening best.

Is you post a screenshot of the graph, you might get some better interpretation here.
Click to expand...

Will do that....
 
Sorry to open an old thread, but I'm curious whether any resolution ever came of these high CHTs on #3. I have the same issue and am trying to figure out if it's a real problem or just the nature of older model 172s.
 
nremmes said:
Sorry to open an old thread, but I'm curious whether any resolution ever came of these high CHTs on #3. I have the same issue and am trying to figure out if it's a real problem or just the nature of older model 172s.
Click to expand...
Same here.
 
I'm guessing you guys are climing around 80 MPH IAS?


O-320 177

Starting altitude of 1,200 MSL with Outside Air Temp 98F Climbing at 90-95 MPH IAS

Full Power 15 minute climb (Full Rich or slightly leaned until I get out of the heat at low altitude)

#3 is hottest with highest I've seen being 420F

In cruise #4 is the usually hottest being around 380F turning 2,500 RPM leaned as much as possible.
 
bnt83 said:
I'm guessing you guys are climing around 80 MPH IAS?


O-320 177

Starting altitude of 1,200 MSL with Outside Air Temp 98F Climbing at 90-95 MPH IAS

Full Power 15 minute climb (Full Rich or slightly leaned until I get out of the heat at low altitude)

#3 is hottest with highest I've seen being 420F

In cruise #4 is the usually hottest being around 380F turning 2,500 RPM leaned as much as possible.
Click to expand...
Many of Cessna's cowlings from a cooling perspective just never seem to be that impressive.
 
jesse said:
Many of Cessna's cowlings from a cooling perspective just never seem to be that impressive.
Click to expand...

Its many 4 banger lycoming powered planes. Just how it is. Grumman's, Cessna's, Mooneys. 500 is redline. When it's hot out, I'd expect and aircooled engine to sweat too.

This airplane does well, 400-420 CHT in climbs only when it's hot outside.

98+, with the humidity to boot, is just damn hot with that giant windshield (greenhouse effect) in it.
 
At 98F at full power 90 mph climb, the front cylinders #1 and #2 are running just under 400 so I don't see a problem
 
bnt83 said:
Its many 4 banger lycoming powered planes. Just how it is. Grumman's, Cessna's, Mooneys. 500 is redline. When it's hot out, I'd expect and aircooled engine to sweat too.

This airplane does well, 400-420 CHT in climbs only when it's hot outside.

98+, with the humidity to boot, is just damn hot with that giant windshield (greenhouse effect) in it.
Click to expand...
David's mooney cools VERY well compared to what I see in 172s.
 
Compromise,


You want more cooling drag to go on an already draggy Cessna 172 just to get a few degrees cooler on a hot day or just climb at a higher IAS on those days?
 
bnt83 said:
Compromise,

You want more cooling drag to go on an already draggy Cessna 172 just to get a few degrees cooler on a hot day or just climb at a higher IAS on those days?
Click to expand...

I want my Cessna to run cooler so I can get a little more cruise speed and a lower fuel burn rate without compromising the longevity of my engine. One engine replacement was enough. But this is not my thread.
 
JOhnH said:
I want my Cessna to run cooler so I can get a little more cruise speed and a lower fuel burn rate without compromising the longevity of my engine. One engine replacement was enough. But this is not my thread.
Click to expand...


More cooling drag = slower in cruise

If you're overheating in cruise there's something wrong.
 
bnt83 said:
If you're overheating in cruise there's something wrong.
Click to expand...

And that is exactly why I have spent thousands of dollars over the past few years trying to find out. I have had two A&Ps and two IAs look at it and it still runs hotter than other similarly configured 172Ns
 
JOhnH said:
And that is exactly why I have spent thousands of dollars over the past few years trying to find out. I have had two A&Ps and two IAs look at it and it still runs hotter than other similarly configured 172Ns
Click to expand...


Is it indication problems or real cooling problems? Lycoming's induction setup sucks, way too many places to leak that go undetected. When did the problems start and what carburetor is installed?
 
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