Winter Flying - Adjust CHT Target?

[WDD]

I have a Continental 0470R, and manage the mixture to be LOP and hit 380 CHT.

In colder temps like yesterday when OAT was around 0 C at 7000 feet, it was hard to get it up to 380. I kept it around 370 because I didn't want to inadvertently get into the dreaded Red Box of death and instant engine destruction.

What do the wise people here do in colder months with their target CHT?

 

[GeorgeC]

I have a Continental 0470R, and manage the mixture to be LOP and hit 380 CHT.

In colder temps like yesterday when OAT was around 0 C at 7000 feet, it was hard to get it up to 380. I kept it around 370 because I didn't want to inadvertently get into the dreaded Red Box of death and instant engine destruction.

What do the wise people here do in colder months with their target CHT?

Hwhat is a "target CHT" ?

"Limits are not goals" - Ted

 

[WDD]

Hwhat is a "target CHT" ?

"Limits are not goals" - Ted

Continental from what I can figure out likes to have a cylinder head temp CHT no more than 400, and for longer engine life and a margin of safety, keep the CHT at 380.

A Mike Busch video offered that that overall CHT is a proxy for cylinder combustion pressure and likelihood for engine knock/detonation. Keeping it around 380 and never above 400 is the target for a Continental. That should keep you out of the red box of death, or something like that.

In this video he mentioned that in lower OAT's you should drop your target CHT.

 

[GeorgeC]

And I spent all that time fixing up my baffling to get my CHTs lower than 380...

"Effects are not causes" - me

 

[WDD]

Ah - it was the POA where I also read about 380 target. In the great sticky on how to make your engine last …

At no point do I want to see CHTs exceed 380F. Continental recommends 380F as their maximum. Lycoming recommends 400F in cruise and 425F in climb as their maximum CHT. The limits are much higher, but these are goals. Remember, the goal here is more longevity.

 

[Ed Haywood]

CHT targets and limits are based on metallurgy. OAT should have no effect.

 

[WDD]

CHT targets and limits are based on metallurgy. OAT should have no effect.

The angle isn't overheating of the metal, but rather that the CHT is a proxy for internal pressure and detonation likelihood. If I have CHT's cooled much more than usual because of cooler than usual air temps, I could theoretically run a mixture closer to peak than would be suggested by the CHT, and thus be closer to / in the re box and creating detonations.

Thus, solely focused on using CHT to help prevent engine detonation, does anyone run lower CHT in the colder winter months?

OPTION 2: Mike Busch and his AOPA videos are addled fiction made of feeble babble. Stop overthinking this, bothering the POA on a Sunday, and go fly.

 

[Rick A]

In the winter when the OAT gets below freezing my Lyc IO-360 cruising CHT's can't get out of the 200's. Not producing adequate cabin heat is the biggest hassle.

Keeping the CHT's as cool as you can while remaining below the red line is probably all I believe you should aim to do. For a normally aspirated engine flying at 7000' MSL (or higher) the dreaded red box doesn't exist at peak, or LOP. Don't sweat it...

 

[455 Bravo Uniform]

So barring any cylinder temp & OAT info, was the back in the ol’ days “lean until stumble, then 3 turns-in” different in the Houston/Miami summer vs the great white north in the winter? It all ended up at the same A/F ratio more or less w/r/t D.A., no consideration for CHT. Food for thought.

 

[WDD]

Doing it that way probably got you 90% of the way there and and engine that ran for 4000 hours

 

[Hang 4]

Thus, solely focused on using CHT to help prevent engine detonation, does anyone run lower CHT in the colder winter months?

The limit numbers that Conti and Lycoming publish are about the metallurgy, not detonation. If you have aluminum cylinders in the mid to high 400's, you will damage them. While CHT is a proxy for cylinder pressure, I'd be looking at %power, lean or rich of peak EGT's (not absolute) and fuel flow. Know your engine.
TL/DR - Don't worry about a 10 degree difference

 

[WDD]

Copy that. Yes, it’s a BOGO. Keep it at 380 to protect metal, but that’s apparently where you’re good for detonation at as well.

But as posted, at 7000 feet not making the power so I shouldn’t worry about red box. Makes sense.

Fuel flow? Yep - got to get that engine monitor.

 

[Racerx]

Mike Busch isn't an oracle. Most of his info is repurposed from someone else. I don't like his leaning technique, it seems a little too arbitrary. I also don't like his reasoning for not leaning to peak egt.

 

[WDD]

If at altitude and power output where I don’t have a red box, and OAT is cool enough I won’t overheat, what do I get for running at peak?

 

[cowman]

I can barely get my CHTs up to 380 in the summer. In the winter I often get cylinders below 300- doesn't matter where I move the mixture knob that's as hot as it will get.

Piper Lance with a Lycoming IO-540 in case anyone is wondering.

 

[Daleandee]

In the winter when the OAT gets below freezing my Lyc IO-360 cruising CHT's can't get out of the 200's. Not producing adequate cabin heat is the biggest hassle.

I fly with an experimental air-cooled engine (Corvair conversion) and CHTs are always quite cool (mid 200's). After thirteen years it still has great compressions, uses no oil between changes, and has been extremely reliable.

As for Lycoming ... I read somewhere that they give 150ºF as the minimum temperature at which a cylinder is ready for full power. As for detonation ... generally the cooler you can keep the cylinders the less concerns you will have with detonation. Personally I believe 380ºF is too hot but that's what Lycoming gives.

As for cabin heat ... I recently added new memory foam to my seats and I'm considering adding some seat heaters too ...

 

[Ed Haywood]

Personally I believe 380ºF is too hot

Not picking on you or being argumentative, but ... what empirical data is your belief based on?

 

[Daleandee]

Not picking on you or being argumentative, but ... what empirical data is your belief based on?

In my very limited experience with air-cooled aircraft conversions (VW, Corvair, Jabiru) when temps get to 380-400 range the aluminum becomes softer and head warping, loosening valve seats, and cracking are found. There are thousands of hours on converted engines flying at much lower temps without issue.

Lycoming uses a 200 series alloy (IIRC) that begins to soften at temps in the upper 300's (392º is cited). So it seems that keeping a bit further from those temps would give longevity to the heads. I would be aiming at 325-350ºF. One reason for the high temps is because of using the 100LL fuel. Higher temps are needed to keep the cylinders clean. Better fuel would eliminate the need to run the engine so hot.

 

[Ed Haywood]

In my very limited experience with air-cooled aircraft conversions (VW, Corvair, Jabiru) when temps get to 380-400 range the aluminum becomes softer and head warping, loosening valve seats, and cracking are found. There are thousands of hours on converted engines flying at much lower temps without issue.

Lycoming uses a 200 series alloy (IIRC) that begins to soften at temps in the upper 300's (392º is cited). So it seems that keeping a bit further from those temps would give longevity to the heads. I would be aiming at 325-350ºF. One reason for the high temps is because of using the 100LL fuel. Higher temps are needed to keep the cylinders clean. Better fuel would eliminate the need to run the engine so hot.

Thanks, that is more empirical than I expected.

 

[MRC01]

If at altitude and power output where I don’t have a red box, and OAT is cool enough I won’t overheat, what do I get for running at peak?

Lycoming uses a 200 series alloy (IIRC) that begins to soften at temps in the upper 300's (392º is cited). So it seems that keeping a bit further from those temps would give longevity to the heads. I would be aiming at 325-350ºF. One reason for the high temps is because of using the 100LL fuel. Higher temps are needed to keep the cylinders clean. Better fuel would eliminate the need to run the engine so hot.

Yep, ideal operation is a tradeoff between too hot and cooking exhaust valves, versus too cold and gunking them up with deposits. Conti guidance runs on the cool side, Lyco on the hot side. Choose your poison.

 

[Racerx]

Yep, ideal operation is a tradeoff between too hot and cooking exhaust valves, versus too cold and gunking them up with deposits. Conti guidance runs on the cool side, Lyco on the hot side. Choose your poison.

Lycoming valves are sodium filled and tend to run cooler.

 

[Rick A]

There are thousands of hours on converted engines flying at much lower temps without issue.
Higher temps are needed to keep the cylinders clean. Better fuel would eliminate the need to run the engine so hot.

Yep, ideal operation is a tradeoff between too hot and cooking exhaust valves, versus too cold and gunking them up with deposits. Conti guidance runs on the cool side, Lyco on the hot side. Choose your poison.

I may have found the balance between cooking and gunk. Zero cylinder problems during the last 15+ years of operating LOP (except in climbs) on a Lyc IO-360 with GAMI's and an instrument monitor. After installing GAMI's around 1200 hours since new, the last engine ran LOP nearly 1500 more hours more before an overhaul was needed (at 1674 hours) when a cam follower started spalling. Upon teardown, the engine was clean as a whistle.

Following leaning past peak, cylinder head temps go lower. Always. Enrich back to peak then ROP and beyond and temps go higher. Always.

On a very hot day with a load the highest cylinder may hit 365F in an ROP climb (good baffling and an aftermarket cowling with large cowl flaps help). On very cold days the highest CHT is in the upper 200's during LOP cruise at altitude. In very hot summer weather flying LOP at altitude, in cruise, the highest CHT is in the 315 to 325 range.

These lower than average cylinder temps don't create gunk. Since flying mostly LOP (except for climbs), the engine remains super clean. That was not the case when operating ROP in accordance with Lycoming's recommendations, and deposits were mostly carbon. Following nearly 1000 hours on the current rebuild (by Zephyr in FL) the oil is still a little yellow after 40 to 50 hours when changed, and only burning a quart every 12 to 14 hours, which in this particular engine is excellent.

IMO, the lower the cylinder temps remain, the better it is for the life of the engine and related accessories. Pushing 400 degrees of CHT (IMO) is kind of high, regardless of what redline CHT the manufacturer declares is maximum. Running higher temperatures to eliminate the creation of gunk may be an unpleasant side effect of running ROP, I don't know. But I do know clean, and (so far) have experienced excellent cylinder life.

No need to mess with anything. The mechanic who installed the GAMI's over 15 years ago said I was crazy, and would be requiring cylinder work in 500 hours or less. He was wrong.

Maybe this engine will once again approach or possibly exceed 3000 hours without anything major happening... which should easily outlive me.

 

[MRC01]

I may have found the balance between cooking and gunk.
...
IMO, the lower the cylinder temps remain, the better it is for the life of the engine and related accessories. Pushing 400 degrees of CHT (IMO) is kind of high, regardless of what redline CHT the manufacturer declares is maximum. Running higher temperatures to eliminate the creation of gunk may be an unpleasant side effect of running ROP, I don't know. But I do know clean, and (so far) have experienced excellent cylinder life.

Running lean of peak can give the best of both sides: cool temps to save the valves, and lean mixtures to avoid gunking them up. Not all engines can do this. Your IO-360 with balanced injectors and advanced engine monitor can - my simple carbureted O-360 cannot.

I still lean as much as I can when under 70% power. Just rich of rough drops about 25 RPM below peak RPM and gives 8 gph at 120 kts in my 172. So far, approaching 900 hours it's burning about 1 qt. of oil every 15 hours, the spark plugs stay clean and the compressions and borescopes are OK. Fingers crossed.

 

[flyingcheesehead]

I have a Continental 0470R, and manage the mixture to be LOP and hit 380 CHT.

In colder temps like yesterday when OAT was around 0 C at 7000 feet, it was hard to get it up to 380. I kept it around 370 because I didn't want to inadvertently get into the dreaded Red Box of death and instant engine destruction.

What do the wise people here do in colder months with their target CHT?

Whoa... Target CHT? As Ted said and @GeorgeC quoted: Limits are not goals!!!

Keep it *BELOW* 380. You should NOT be trying to get to 380! The strength of the metals falls off dramatically above 400. Don't set mixture with CHT.

Ah - it was the POA where I also read about 380 target. In the great sticky on how to make your engine last …

At no point do I want to see CHTs exceed 380F. Continental recommends 380F as their maximum. Lycoming recommends 400F in cruise and 425F in climb as their maximum CHT. The limits are much higher, but these are goals.

I'll let @Ted jump in and verify (or contradict) what I say here, and hopefully edit the sticky post too, but I believe what he meant by this is that your *goal* should be to use 380F as your *limit* in spite of the fact that both Conti's and Lycoming's CHT *limits* are much higher (460 for Conti, 475-500 for Lyc!). As he's also the guy who says "Limits are not goals", I do NOT think he meant that you should try to get your CHT up to 380.

The angle isn't overheating of the metal, but rather that the CHT is a proxy for internal pressure and detonation likelihood. If I have CHT's cooled much more than usual because of cooler than usual air temps, I could theoretically run a mixture closer to peak than would be suggested by the CHT, and thus be closer to / in the re box and creating detonations.

Right, which is why you shouldn't be trying to get your CHT up to 380 in the first place. You want your CHTs to all be below 380.

Thus, solely focused on using CHT to help prevent engine detonation, does anyone run lower CHT in the colder winter months?

CHTs do run lower in the winter... And you shouldn't be running your engine harder in an attempt to get up to 380, ever. FWIW, in the summer my CHTs run 300-350 in cruise. In the dead of winter, sometimes I don't even get up to 300 in cruise. Climb is maybe 30-40 degrees warmer than cruise, though I tend to climb at pretty high airspeeds.

Mike Busch isn't an oracle. Most of his info is repurposed from someone else.

... Most of it from George Braly, John Deakin, and Walter Atkinson, who ran Advanced Pilot Seminars and brought this stuff to the masses.

Deakin's columns on AvWeb are pure gold, and should be required reading for anyone who owns an airplane or flies something other than a trainer. https://avweb.com/features/pelicans-perch-index/

If at altitude and power output where I don’t have a red box, and OAT is cool enough I won’t overheat, what do I get for running at peak?

In theory, at peak is the most efficient mixture, as it is the perfect stoichiometric fuel/air ratio and (again in theory) you won't have any unburned fuel or unused oxygen coming out of the exhaust.

That said, each cylinder's mixture is slightly different, so "at peak" still isn't. Also, there are more variables involved than just how much oxygen and fuel get used, such as the speed of flame propagation vs spark timing which affects the angle at which the connecting rod transfers the linear motion of the piston to the crankshaft.

Being a Mooney owner and thus going for peak efficiency, here's what I do:
1) No more than 65% power in cruise.
2) All else being equal, lower RPM (= lower friction losses and thus more power to the prop) and higher MP (= lower pumping losses and thus more power to the prop). My engine is supposed to run no lower than 2300 RPM, so I run it at 2300 RPM except in the climb, and I run it WOT above about 6500 feet.
3) At altitudes up to about 9,000 I lean up until my richest cylinder is about 10ºF LOP. When I let it settle out that cylinder will end up about 25ºF LOP. As I climb higher and make less power, I'll transition to running it closer to peak. If I have 3 cylinders LOP and 3 ROP that's as close to "at peak" as I'll get. If I'm above about 13,000 I'll be closer to best power mixture, 100 ROP. I've had my plane to FL190 (despite being normally aspirated) but I generally don't go that high unless terrain, weather, or glide to shore is an issue - Like any normally aspirated plane, it's happiest around 9,000 give or take a couple thousand.

 

[Racerx]

Whoa... Target CHT? As Ted said and [

... Most of it from George Braly, John Deakin, and Walter Atkinson, who ran Advanced Pilot Seminars and brought this stuff to the masses.

Deakin's columns on AvWeb are pure gold, and should be required reading for anyone who owns an airplane or flies something other than a trainer. https://avweb.com/features/pelicans-perch-index/

And Busch even admits to departing how APS describes leaning. But to me he's never really been able to coherently explain why he doesn't use egt.

Deakins articles are fantastic. Specifically "manifold pressure sucks", "those marvelous props", and "mixture magic"

 

[WDD]

You want your CHTs to all be below 380.

What then is your lower temp limit?

 

[Rick A]

Being a Mooney owner and thus going for peak efficiency, here's what I do:
1) No more than 65% power in cruise.
2) All else being equal, lower RPM (= lower friction losses and thus more power to the prop) and higher MP (= lower pumping losses and thus more power to the prop). My engine is supposed to run no lower than 2300 RPM, so I run it at 2300 RPM except in the climb, and I run it WOT above about 6500 feet.
3) At altitudes up to about 9,000 I lean up until my richest cylinder is about 10ºF LOP. When I let it settle out that cylinder will end up about 25ºF LOP. As I climb higher and make less power, I'll transition to running it closer to peak. If I have 3 cylinders LOP and 3 ROP that's as close to "at peak" as I'll get. If I'm above about 13,000 I'll be closer to best power mixture, 100 ROP. I've had my plane to FL190 (despite being normally aspirated) but I generally don't go that high unless terrain, weather, or glide to shore is an issue - Like any normally aspirated plane, it's happiest around 9,000 give or take a couple thousand.

Been running my 200hp Lyc a little differently, but close to your methods. I believe you have one of the higher hp models (Ovation?) which is LOP friendly per engine manufacturer consent, so maybe you have some official guidelines beyond any unofficial recommendations from the gurus at Advanced Pilot Seminars.

I run WOT from takeoff to slowing down approaching the airport environment to land. Climbs are done at 2450 - 2500 rpm above the Red Zone at around 130 to 160 degrees ROP. Cruise at or below 65% power LOP at 2300 to 2350 RPM's at whatever (depending upon altitude) negative LOP value runs smoothly with the lowest fuel flow, generally 10 degrees F to 60 degrees F LOP (resulting in 7.2 to 8.5 gallons per hour depending upon altitude). This results in a TAS loss of 8 to 12 kts.

One big advantage enjoyed while running cool is that I no longer bother (as compared to the old days of ROP operations) to slowly cool the engine down on descents by reducing MP an inch or two at a time. Now, I just remove a couple of handfuls of throttle (like a turbine) when needed to slow down to gear extension speed. Figuring the engine is running cool already, and shock cooling is no longer a concern. So far, so good...

 

[Rick A]

And Busch even admits to departing how APS describes leaning. But to me he's never really been able to coherently explain why he doesn't use egt.

IMO the only importance of EGT is finding one or all temperatures higher than normal. Indicating the likelihood of a magneto failure, exhaust valve or exhaust gas plumbing irregularity. Certainly nothing of value for setting power.

 

[GeorgeC]

What then is your lower temp limit?

There isn't one. I don't remember what I'd get in the 182, but in my 140, in the summer I'll get 330 in cruise. In the winter, you get what you get...

 

[WDD]

There isn't one. I don't remember what I'd get in the 182, but in my 140, in the summer I'll get 330 in cruise. In the winter, you get what you get...

Interesting. Food for thought. The engine needs to be a certain temperature for it to work as designed. Not only the oil to flow, but the metals need to get hot enough to expand and fit as designed.

I'll toss out for discussion that an engine can be too cold for longevity, too cold to work efficiently, not sealing, etc.

So maybe running my Continental between 360 and 380 on the hottest cylinder would give me good engine operation as well as long life. Yeah or Nah? Thoughts?

BTW - I am picking up great info from this thread. Appreciate the comments, hope others getting something out of this as well.

 

[Hang 4]

The issue with running too cold is the potential to build up lead deposits on valve stems and other areas. That can lead to a stuck valve. The other one is the oil needs to be hot enough to vaporize the water that is a combustion by product.
The one other issue with using absolute CHT #'s is that every plane is different. Baffling for one example. Excessively high CHTs can be poor baffling, timing (bad mag).
Know your engine and play around a bit when you have time. Try leaning more/less and give the data time to stabilize. For my plane, I have an economy cruise setting that is based on fuel flow, % power and pressure altitude. I also have a fast cruise where I keep a closer eye on CHT as I get nearer the "red box" due to % power. I found a bad mag from those temperatures getting too high in spite of being right in a normal zone.

 

[GeorgeC]

The issue with running too cold is the potential to build up lead deposits on valve stems and other areas. That can lead to a stuck valve.

That's a ground ops EGT thing, not a cruise CHT thing...

The other one is the oil needs to be hot enough to vaporize the water that is a combustion by product.

That's a ground running/too short of a flight thing, not a cruise CHT thing...

So maybe running my Continental between 360 and 380 on the hottest cylinder would give me good engine operation as well as long life. Yeah or Nah? Thoughts?

"You know, I worry that my engine is running too cold in cruise."
-nobody ever

The bad news is that fixating on numbers will get worse when you get an engine monitor The good news is that it gets better when you start to see the forest for the trees.

PM me your address, I think I have an O470 operators manual I can drop in the mail to you.

 

[Hang 4]

Why then do they have winter block off plates to keep oil temps up? You can definitely have oil too cold in cruise.
And yes, you can run too cold in cruise to prevent lead bromide deposits from forming. Kind of an edge case and running pig rich also contributes.
That's why one absolute # for things really doesn't make sense. High and low limits yes, but there's a lot of room between those two. Too high and metal suffers, too low and other factors come into play.

 

[Ted]

Ah - it was the POA where I also read about 380 target. In the great sticky on how to make your engine last …

Appreciate that you liked my thread

The goal is to keep CHTs at or below 380F, as opposed to the limit of keeping them below some higher temperature (I forget the limit on Continentals, I want to say 450-465F?). The intent is NOT to adjust your mixture to potentially increase CHTs vs. your normal practices and to raise them to 380F.

There is, at some point, a lower limit, and a lower goal. Oil temp wise, you do want your oil to be around 180F, and that's more of a year round number. That keeps the oil hot enough that water will boil out. This is because you're at an altitude above sea level so boiling temperature decreases, and also because there are hot spots in the engine where the oil will get hotter than that 180F. Too much colder and you deal with condensation issues in the oil, too much hotter and eventually the oil gets too hot.

CHT wise, I forget where that lower goal ends up being. I've really never seen it become an issue in practice, and is probably the sort of thing that you'd run into more in Alaska or Canada. But even flying on days and temperatures well below freezing (and closer to/below 0F) it's never practically created a problem other than me keeping myself warm. Generally, it ends up being fairly hard to get CHTs below 300F, just because combustion is hot. I seem to recall something around 300F was generally considered to be the lowest you wanted to see, and that seems about right to me. Again, not something I ever saw in practice.

IMO the only importance of EGT is finding one or all temperatures higher than normal. Indicating the likelihood of a magneto failure, exhaust valve or exhaust gas plumbing irregularity. Certainly nothing of value for setting power.

This view is commonly stated regarding EGT, and goes back to Mike Busch and the APS folks. I disagree vehemently with it. Engines are made out of metal. It will eventually melt, and before that it will start to have issues, including burned valves (as in, actually burning them, not just seeing indications of a burning valve). This is often justified with saying things like "There's no published limit" or "EGT probes are inaccurate". Again, a limit does exist within the metal itself, regardless of whether it's put in a POH. And in my experience, which includes thousands of hours on fully instrumented dynos and flight stands (plus thousands of hours flying piston engines with engine monitors), my experience is that EGT probes are pretty accurate in absolutes, not just in relative numbers.

1550F is the number I try to stay below for both EGT and TIT. In low horsepower engines (parallel valve Lycomings, for instance) you pretty much won't get there. In higher powered engines and especially turbocharged engines, it's something to watch out for. It can also get influenced by things such as improper ignition timing, which happened to me on the 414 right before doing multiple hurricane relief flights to St. Croix after hurricane Maria. End result? 5 burned exhaust valves.

 

[Mtns2Skies]

Why then do they have winter block off plates to keep oil temps up?

Oil temp != CHT

This thread is just rage bait... right?

 

[Rick A]

1550F is the number I try to stay below for both EGT and TIT. In low horsepower engines (parallel valve Lycomings, for instance) you pretty much won't get there.

Agree 100%. Regardless of the power configuration and operating conditions, my IO-360's EGT's always seem to be registering somewhere in the 1300's, typically in the lower 1300's.

Hence my belief that EGT readings are only useful (to me and probably many other lower horsepower powered normally aspirated engines) when one or more cylinders shows an unusual increase (or in the case of a leaking exhaust seal or pipe, a decrease of EGT outside of the normal temperature range).

 

[Ed Haywood]

IMO EGT is far more useful than CHT.

 

[Martin Pauly]

What then is your lower temp limit?

As others have said, there isn't one. Realistically, when the oil is above its minimum temperature, the engine is warm enough.

A few years ago I discussed this with George Braly from GAMI. At the time, Mike Busch had just gone public with a recommendation to consider 350 deg F a minimum CHT to avoid deposit buildups. That was new information to me, and I wanted an expert opinion. George told me that Continental had worked on a liquid-cooled version of their IO-550 engine, and they were targeting to maintain a CHT around 250 deg F. That was all I needed to hear to dismiss Mike's recommendation for my Continental engine.

I do not consider CHT a target for anything. EGT can be a useful target; then CHT helps to make sure the engine is happy. Maybe a good analogy is the difference between control and performance instruments for instrument flying. Control the engine by reference to EGT; monitor its performance with CHT.

As was said earlier, CHT is a proxy for ICP (internal cylinder pressure). In the winter months, the same ICP is results in lower CHTs than in the summer months, due to better cooling. Naturally, during the winter months CHTs are usually colder anyway, so it's not really a practical issue AS LONG AS YOU DON'T AIM FOR A CONSTANT TARGET CHT (which would be hard to reach in the winter).

CHT trends are just as important than the absolute value. If you see a CHT rise unusually quickly and you don't know what pilot input let to this rise, it is possible you are experiencing detonation or (worse yet) pre-ignition. Lower the power, enrichen the mixture - do whatever it takes to stop the trend.

- Martin

 

[WDD]

IMO EGT is far more useful than CHT.

I do not consider CHT a target for anything. EGT can be a useful target; then CHT helps to make sure the engine is happy. Maybe a good analogy is the difference between control and performance instruments for instrument flying. Control the engine by reference to EGT; monitor its performance with CHT.

Interesting in that is 180 degrees - no pun intended - from those Mike Busch videos. CHT is everything, EGT is not meaningful.

 

[Daleandee]

As others have said, there isn't one. Realistically, when the oil is above its minimum temperature, the engine is warm enough.

Actually there is (for the 360 series) and it's listed here:

Operator’s Manual Lycoming O-360, HO-360, IO-360, AIO-360, HIO-360 & TIO-360 Series:

https://www.lycoming.com/sites/default/files/file/2025-11/60297-12%20-%20O-360%2C%20HO-360%2C%20IO-360%2C%20AIO-360%2C%20HIO-360%2C%20and%20TIO-360%20Series.pdf

Several places in this manual read:

"At Bayonet Location For maximum service life of the engine maintain cylinder head temperature between150°F and 400°F during continuous operation."

Obviously this is only for the engines listed but it does give guidance as to what Lycoming likes for lower CHT limit.