Cylinder Head Temperatures

Pablo Canales

Pablo Canales

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Pablo
Hey guys! I’ve been having a question lately, but no one seems to have a clear answer.

I have a JPI EDM-700 installed on my Cessna 205
With a Continental IO-550

The thing is, that it shows the head temperatures digitally, but it doesn’t have a Green or Red arc.

On climbs temperatures would normally go above 415°F on Cylinders 1,3 and 6

And during cruise flight around 350°-380°

How Hot is TOO HOT?

The original Cessna manual says never go above 450°F
But some pilots and the Continental Website recommend always below 380°F

It seems almost impossible to stay below 400°F even with 50% power


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Multiple instances of this thread have been consolidated into a single thread.

Nauga,
and a big plunger
 
Pablo Canales said:
Hey guys! I’ve been having a question lately, but no one seems to have a clear answer.

I have a JPI EDM-700 installed on my Cessna 205
With a Continental IO-550

The thing is, that it shows the head temperatures digitally, but it doesn’t have a Green or Red arc.

On climbs temperatures would normally go above 415°F on Cylinders 1,3 and 6

And during cruise flight around 350°-380°

How Hot is TOO HOT?

The original Cessna manual says never go above 450°F
But some pilots and the Continental Website recommend always below 380°F

It seems almost impossible to stay below 400°F even with 50% power


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Click to expand...

Been to a few mtx seminars on this. I’m currently at one now and there was discussion on this today. Like all big bore Continentals, I believe the IO-550 is also limited to 460F. The 470, 520, and 550’s get hot on TO. A CHT of 380 is the cruise temp. My 470 gets to 415-420 on take off. I keep it below 380 in cruise.

The myth is to remove MP before RPM after take off. That is a myth. What is taught by the engine experts such as Mike Bush and others is to keep MP full forward and only reduce RPM after TO. Lean the mixture as you climb but keep MP at full power until you need to reduce it for descent and landing. This allows the engine to maintain power, efficiency and cooling.

The CHT of 400-420 is only a couple minutes before RPM reduction. The airplane begins to accelerate which also creates cooling. Reducing the RPM to a climb RPM setting with full MP, and a rich mixture climb will greatly reduce the CHT from the 400’s to below 390.

Continental has published an ops and mtx manual on these engines with limitations. It’s a good read. Getting the manual based on which 550 you have is another issue.


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Fearless Tower said:
Depends on the engine.

Big bore Continentals hate heat. I would be very concerned with a Continental running 400F or more on climb out.
Click to expand...

I’ll agree to disagree. I would not be concerned seeing 400-425 on take off, especially if it begins to reduce as you accelerate and reduce RPM. If the CHT continued to increase above 425 as you increase speed and reduce RPM, then I would definitely be concerned.


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Maybe you should check your baffling to make sure it is good?

Also check with Cessna forums to see if this is common for your model.

My CHT alarm is set for 400° and I rarely hit it, but I don’t climb at Vy either.
 
Fracpilot said:
The myth is to remove MP before RPM after take off. That is a myth. What is taught by the engine experts such as Mike Bush and others is to keep MP full forward and only reduce RPM after TO. Lean the mixture as you climb but keep MP at full power until you need to reduce it for descent and landing. This allows the engine to maintain power, efficiency and cooling.
Click to expand...

I agree, but didn’t know it was such a common myth. I’ve never made practice of pulling MP back after takeoff. Full MP all the way up. Depending on altitude and objective I might not ever pull the MP back until top of descent. More common than not for the typical xc flight.
 
Jdm said:
I agree, but didn’t know it was such a common myth. I’ve never made practice of pulling MP back after takeoff. Full MP all the way up. Depending on altitude and objective I might not ever pull the MP back until top of descent. More common than not for the typical xc flight.
Click to expand...

I guess it depends how old you are and when you learned to fly airplanes with CS props. I lot of older pilots like me have had this engrained in their head that you must pull MP before RPM or you’ll damage the engine.

I recently flew with a very experienced and highly respected test pilot. He told me the same thing that you must pull MP before RPM and I just sighed while shaking my head.

I too was taught the same thing over 30 years ago, only to learn throughout years of research and experience that it’s just some old wives tale. I am curious of the origin of it. I’m told Doolittle flew his B25’s also at full MP and controlled power with RPM and CHTs with mixture.


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We’re pretty close, I got my pp in 1987. Didn’t fly anything large or cs props until 2000ish though. It does seem like I remember hearing something about over or under squared being mentioned.
 
Fracpilot said:
I guess it depends how old you are and when you learned to fly airplanes with CS props. I lot of older pilots like me have had this engrained in their head that you must pull MP before RPM or you’ll damage the engine.

I recently flew with a very experienced and highly respected test pilot. He told me the same thing that you must pull MP before RPM and I just sighed while shaking my head.

I too was taught the same thing over 30 years ago, only to learn throughout years of research and experience that it’s just some old wives tale. I am curious of the origin of it. I’m told Doolittle flew his B25’s also at full MP and controlled power with RPM and CHTs with mixture.


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Click to expand...


I’m much more concerned with pushing in RPM while under power. Mine will overspeed very quickly.
 
If you are getting CHTs above 400 you need more fuel flow....should have something in the +32 gph range.
 
I’m not Busch nor do I disagree or agree with everything he says, and I’m no A&P. I’m here to learn, not argue....and not sure if this is the right page or time to derail this thread, but it’s only the internet, so what the heck:

To me, pulling RPM in an airplane is akin to putting a brake or a load on the crank. It’s not really reducing RPM by lessening fuel and air, its turning the prop blades to get more bite - flattening and increasing air resistance so the crank can’t turn as fast as the burning mixture is forcing the pistons and rods to. This puts more load (force) on the rotating assembly. And the heads also see more load, but I think temps go down, because of less combustion cycles per time. So RPM controls temp, not load. I would not think that looking at CHT and EGT tells you the whole story of what the crank and rods “feel”.

Yeah, taken to the other extreme, you could remove the prop angle altogether (its finest setting) and redline the engine and fail the rotating assembly due to over speed and the rods or crank not being able to withstand the energy of high speed motion. But we’re talking operation under redline and I just wanted to get it out there that the other extreme doesn’t make sense either.

So lower RPM lowers head temps, but increases engine load, if all else is staying equal. True? Or not? I think true.

Reducing both load and temp are good. But pulling RPM using propeller angle increases load while decreasing temp due to less combustion cycles per time. I think we need to think about both.

Stress leads to fatigue which leads to failure. Stress is high temperature and high load. I’d rather fail a valve than a rod, but high temps don’t just impact the cylinder head exhaust valve, heat is bad for a lot of other reasons to the head and other components. Heat is wear & tear.

I don’t want to lose an engine, no one does. My life and my wallet get hurt. But I’d rather it not break on climb out if given a choice of when to blow.

I’m going to keep pulling black first and then the blue, in that order, but pretty much within 5-10 seconds of each other. IO-470.
 
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Capt. Geoffrey Thorpe said:
That's how you save fuel.
Click to expand...

Pulling MP would also save fuel. especially while reducing mixture. But they left it full forward.

I fly my 310 the same way. It works great. TAS Aviation, Saavy, and many other experts recommend the same procedure of MP full forward, reduce RPM and lean as necessary.


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I would normally use 25inches of Manifold and 2500rpm’s for takeoff

And for climbing and cruise I will pull back both to
22inches and 2300rpm’s
Or 21inches and 2200rpm’s


What do you guys think?


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Pablo Canales said:
I would normally use 25inches of Manifold and 2500rpm’s for takeoff

And for climbing and cruise I will pull back both to
22inches and 2300rpm’s
Or 21inches and 2200rpm’s


What do you guys think?


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Click to expand...

[mention]455 Bravo Uniform [/mention]


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455 Bravo Uniform said:
I’m not Busch nor do I disagree or agree with everything he says, and I’m no A&P. I’m here to learn, not argue....and not sure if this is the right page or time to derail this thread, but it’s only the internet, so what the heck:

To me, pulling RPM in an airplane is akin to putting a brake or a load on the crank. It’s not really reducing RPM by lessening fuel and air, its turning the prop blades to get more bite - flattening and increasing air resistance so the crank can’t turn as fast as the burning mixture is forcing the pistons and rods to. This puts more load (force) on the rotating assembly. And the heads also see more load, but I think temps go down, because of less combustion cycles per time. So RPM controls temp, not load. I would not think that looking at CHT and EGT tells you the whole story of what the crank and rods “feel”..... IO-470.
Click to expand...

This is an insightful paragraph, but there are a couple of things to consider here. Reducing RPM does so by changing the governed speed. The blade angle does increase to reduce RPM but once the lower RPM is established the blade AOA is reduced again and constantly adjusted to keep the RPM at the new lower RPM setting. Yes, the overall angle will be more than at higher RPM at the same airspeed, but the tip losses will also be less because of reduced tip speed which also decreases noise. The engine torque output varies along the engine torque lug curve, which the prop governor will automatically follow to maintain RPM, and this is likely to vary some be about the same near max RPM. The piston ring friction, the highest internal friction load, will drop with the square of piston speed. Overall power will be reduced along with fuel and air consumption, and overall prop efficiency will improve slightly. Combining all the factors means that the engine pressure stress will not be increased by reducing RPM, unless torque also increases too.

If the advance engine management people are correct, then at any given constant power setting stress varies dramatically with fuel-air ratio. This is because flame propagation and burn time changes as the mixture setting changes. The fastest flame burn time occurs about 50degF ROP, and at maximum power this likely puts the timing of peak internal cylinder pressure too close to TDC to perform useful work, thus causing internal pressures to be higher without generating more torque. The Advance engine management people also teach that cylinder head temperatures can be used as a poor man's strain gauge to keep track of it all. CHT drops as the mixture is richened or leaned from peak CHT.

Because of all of this, if I was worried about high CHT during takeoff and climb, I would want to be sure my engine is running rich enough at maximum power to keep it cool. By my calculations 100F ROP is 13.6 HP per GPH, 150F ROP is 12.37 HP per GPH, and 200F ROP is 11.20 HP per GPH. I would want to be able to get to at least 150F ROP or richer. On my Mooney that is 200HP/12.37 = 16.16 GPH. That is close to what mine pulls, but I am a little light. I had a discussion with someone recently that is way too lean during the climb. We identified it because his EGT increases during the climb instead of decreasing.

Hope this helps
 
Fracpilot said:
Pulling MP would also save fuel.
Click to expand...
Pulling manifold pressure (closing the throttle) reduced the thermodynamic efficiency of the engine by causing the engine to do work during the intake stroke.
The following is from an auto engine, but the basic cycle is the same. (https://patents.google.com/patent/US8336521) At part throttle, the area B, (which is lost work) is larger. Some of the things the auto industry spends metric buttloads of money on, such as variable cam timing, are primarily intended to reduce the pumping losses (area B) to improve fuel economy. The random patent I grabbed the diagram from is for a "skip fire variable displacement" concept.
upload_2022-2-27_11-12-46.png
 
Pablo Canales said:
Hey guys! I’ve been having a question lately, but no one seems to have a clear answer.
I have a JPI EDM-700 installed on my Cessna 205
With a Continental IO-550
How Hot is TOO HOT?
The original Cessna manual says never go above 450°F
Click to expand...
Why don't we consult the authority on the whole thing instead of bantering CHT opinions about? From the Type Certificate Data Sheet (TCDS) for the IO-550 series:

upload_2022-2-27_11-2-35.png

https://rgl.faa.gov/Regulatory_and_...d92ef6be8625854300448770/$FILE/E3SO_Rev12.pdf
 
Capt. Geoffrey Thorpe said:
Pulling manifold pressure (closing the throttle) reduced the thermodynamic efficiency of the engine by causing the engine to do work during the intake stroke.
The following is from an auto engine, but the basic cycle is the same. (https://patents.google.com/patent/US8336521) At part throttle, the area B, (which is lost work) is larger. Some of the things the auto industry spends metric buttloads of money on, such as variable cam timing, are primarily intended to reduce the pumping losses (area B) to improve fuel economy. The random patent I grabbed the diagram from is for a "skip fire variable displacement" concept.
View attachment 104990
Click to expand...

I’m not sure what you’re getting at here. Auto engines also have computers that regulate a lot of the engine and completely different gearing changing engine loads.


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Fracpilot said:
I’m not sure what you’re getting at here. Auto engines also have computers that regulate a lot of the engine and completely different gearing changing engine loads.
Click to expand...
The thermodynamics are the same. Closing the throttle increases pumping work and reduces efficiency.
The computers and gizwaws on auto engines are (in part) doing what they can to avoid reducing manifold pressure. In an aircraft, the pilot can do the same by not pulling the black knob. Reducing MP does reduce fuel flow, but not in the most efficient manner.
 
I believe the IO-550 operating manual says 420° is the target limit for normal operations. Short durations to that in climb should be no issue, especially since cruise temps are pretty much ideal.

An approved replacement temp instrument should have some indicators for low and high temp limits. The high limit for CHT is 460° so hopefully you never see it. There is no low limit. You should see a low limit for oil temp. Usually a yellow or red light until 70°F and then it should be green. Again, with oil temp high limit at 240° you’ll likely never see it.
 
I've got two TCM TSIO520s to worry about. I have researched this A LOT. There is nothing good that can come running these engines over 400dF in any phase of flight. If yours are hotter than this, I would suspect your fuel flow is too low and/or your baffling could be improved. I have spent countless hours tweaking both, and it's paid off. I never see over 390dF, and at OATs around ISA 380 is the max. Yes, at one time Continental proved the engine doesn't blow up at 460. But do a little internet search for how the properties of aluminum start to change around 400. It's your engine. It's your money.
 
Check fuel flow (the old "SID97" which is now in M-0, for your engine...available on csob)
Verify timing
Close inspection of baffling
Pilot technique (climb airspeed/power settings)
Any time past 400F makes me imagine liquified aluminum (not true of course but I think those valve guides start to wear out, maybe contributes to head cracks.)
 
Last edited:
Pablo Canales said:
I would normally use 25inches of Manifold and 2500rpm’s for takeoff

And for climbing and cruise I will pull back both to
22inches and 2300rpm’s
Or 21inches and 2200rpm’s


What do you guys think?


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Click to expand...
Unless you're departing a high altitude airport, I'm pretty sure your POH says to take off with all three levers all the way forward. Your fuel controller, if set according to the TCM M-O service manual, is set up this way. Why would you do something differently (like 25", 2500rpm)?
 
Lance F said:
Unless you're departing a high altitude airport, I'm pretty sure your POH says to take off with all three levers all the way forward. Your fuel controller, if set according to the TCM M-O service manual, is set up this way. Why would you do something differently (like 25", 2500rpm)?
Click to expand...

Because anything higher than that would rocket the temperatures above 400°

Also, yesterday the mechanic said we could try Retarding the ignition timing to 20 instead of 22
To get lower CHT’s

What do you guys think?


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This is what I’m getting at full power 25.7gph

Mechanics say its fine, but i feel like its not enough to keep the temps down

ce52b174798f7808f499f4d00acfd4b9.jpg



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What's your setup for the engine monitor? Do have any data?

With good baffling and reasonable climb speed, it's possible to keep CHT way below 400 without messing with things like timing.

Here's a chart from savvyaviation.com of the "maximum CHT during flight" for a normally aspirated IO-550. Savvy provides several measures, this one "Measures the maximum CHT attained during each flight, most likely during climb phase." The data points are specifically for my engine for each flight. The percentile lines are for the entire fleet for my engine model, at least those that upload data to savvyaviation.com.

The green percentile line shows that 50% of IO-550 flights, by all owners, do not exceed a CHT of 362*F, not even briefly during climb.
CHT-graph.jpg
 
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NoHeat said:
What's your setup for the engine monitor? Do have any data?

With good baffling and reasonable climb speed, it's possible to keep CHT way below 400 without messing with things like timing.

Here's a chart from savvyaviation.com of the "maximum CHT during flight" for a normally aspirated IO-550. Savvy provides several measures, this one "Measures the maximum CHT attained during each flight, most likely during climb phase." The data points are specifically for my engine for each flight. The percentile lines are for the entire fleet for my engine model, at least those that upload data to savvyaviation.com.

The green percentile line shows that 50% of IO-550 flights, by all owners, do not exceed a CHT of 362*F, not even briefly during climb.
View attachment 105140
Click to expand...

What readings are you normally getting for the EGT’s?

Just to have some reference


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Pablo Canales said:
What readings are you normally getting for the EGT’s?

Just to have some reference


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Click to expand...
You can't compare EGT's between planes. Probes can be installed in very different positions from one plane to the next. It would be meaningless.
 
Checkout_my_Six said:
your fuel flow is too low.....needs to be 30-32 gph
Click to expand...
Where do you see that?


upload_2022-3-4_10-32-49.png

upload_2022-3-4_10-33-13.png

upload_2022-3-4_10-33-35.png

upload_2022-3-4_10-32-20.png

If he doesn't have an IO-550-A he might be a little low, and that could be part of the problem, for sure. But 30-32 would cause a bunch of other troubles.
 
455 Bravo Uniform said:
This puts more load (force) on the rotating assembly.
Click to expand...
More load? How so? An engine produces less power at the lower RPM. If peak power is 2,700 and you reduce RPM to 2,500, that sees a lower power. It's a psychological thing akin to shifting into the wrong gear on a bike and feeling a much harder push on your legs, but it's not at all the same. You want as much air and fuel going into the engine, so you keep throttle and mixture open, but you can make it spin slower and produce less power. You're not really 'lugging' the engine like you would in a car flooring it at 1,500 RPM. You may be getting closer to the torque peak, but torque <> power.

Cirrus has big Conti's that have a tendency to get hot, both CSIP courses I took taught to leave full power and full rich until cruise. If you're too hot, climb at a faster airspeed or step climb
 
Not sure which IO-550 you have. If it's the tune induction N or similar model the continental manual specifies cylinder head temps:
"Normal Operational Temperature (cruise) 420°F 215°C Maximum Allowable Operational Temperature 460°F 238°C Minimum Takeoff Temperature 240°F"
 
My max fuel flow is adjusted to the top end of the range allowed by the manufacturer, and the reason is to keep CHT reasonable during climb.

My engine management is like this: for the first 1000’ AGL, climb at Vy with max fuel flow, and full rich unless there’s density altitude. After climbing 1000’, for the remainder of the climb I pitch down to climb at about 115 kts indicated (that’s to keep the CHT down) and gradually lean the mixture keeping the EGT at about 1300. At the top of climb, pull back on the throttle to maybe 65-70% power while still ROP. Then a “big pull” of the mixture to go LOP and adjust to 50*F below peak for the remainder of cruise, at about 65% power. The engine loves it - it’s now well past TBO and making no metal.
 
Tantalum said:
More load? How so? An engine produces less power at the lower RPM. If peak power is 2,700 and you reduce RPM to 2,500, that sees a lower power. It's a psychological thing akin to shifting into the wrong gear on a bike and feeling a much harder push on your legs, but it's not at all the same. You want as much air and fuel going into the engine, so you keep throttle and mixture open, but you can make it spin slower and produce less power. You're not really 'lugging' the engine like you would in a car flooring it at 1,500 RPM. You may be getting closer to the torque peak, but torque <> power.

Cirrus has big Conti's that have a tendency to get hot, both CSIP courses I took taught to leave full power and full rich until cruise. If you're too hot, climb at a faster airspeed or step climb
Click to expand...

Because the RPM is reduced by increasing the work that the engine must do to move a flatter prop through air (fluid). Is a prop strike the most extreme case? Will my rotating assembly have a higher probability of becoming trash if I strike asphalt or a cat? At 2600 rpm or 800?

This is hangar flying and calls for a real or fake beer.
 
I have an IO-550B in my F33a Bonanza. I too had problems with high CHTs after takeoff in initial climb. If you go onto beechtalk - a forum where the owner base is flying behind big bore continentals, you will find that the general concensus and that has been blessed by GAMI is that the IO550 NEEDS 30-32GPH of fuel flow on takeoff at sea level. Yes this is higher than what is in the continental manual. Get your mechanic to adjust your takeoff fuel flow and verify your baffles are completely sealed. DO NOT reduce manifold pressure in climb. My CHTs now never even get close to 400. The guys at GAMI have come out with research that shows extremely accelerated wear starts occurring over 400. The 460 in the manual is the temp in which I would assume irreversible damage would almost instantly be taking place. Get your fuel flow adjusted, get GAMI injectors, and run LOP in cruise. Your CHTs will be lower than you've ever seen guaranteed.
 
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