Hottest cylinder CHT at cruise

[Wildhorsetrail]

Which cylinder on IO-360 is hotter at cruise settings? And what's the hottest number you've seen?

[Marauder]

Which cylinder on IO-360 is hotter at cruise settings? And what's the hottest number you've seen?

I’m not sure which IO-360 you have and which Mooney it is installed in, but I will typically see either #1 or #3 as the hottest cylinder. It seems that #1 will run hotter in cooler OATs while in warmer OATs (above 15°C), #3 runs hotter.

Depending on the outside OAT, I will see temps in the low 300s up to around 340° on warmer days in cruise. I usually run ROP.

On climb outs, I will adjust the climb rate to keep the cylinders below 380°. But that is rare that it will get close to 380° unless it is really hot out.

I climb at Vy+10 and I have an F model with the lower cowl enclosure.


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[Shadrach]

 Correct baffle/baffle seal alignment is crucial for number cylinder #3. If not properly aligned, there is little to no pathway for air around the backside of the cylinder.

Edited August 5, 2023 by Shadrach

[Ragsf15e]

7 hours ago, Marauder said:

I’m not sure which IO-360 you have and which Mooney it is installed in, but I will typically see either #1 or #3 as the hottest cylinder. It seems that #1 will run hotter in cooler OATs while in warmer OATs (above 15°C), #3 runs hotter.

Depending on the outside OAT, I will see temps in the low 300s up to around 340° on warmer days in cruise. I usually run ROP.

On climb outs, I will adjust the climb rate to keep the cylinders below 380°. But that is rare that it will get close to 380° unless it is really hot out.

I climb at Vy+10 and I have an F model with the lower cowl enclosure.


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Weird that you see #1 warm too.  My #3 is always hottest and my #1 always coolest.  I thought they were all like that?

[Ragsf15e]

3 hours ago, Shadrach said:

 Correct baffle seal alignment is crucial for number cylinder #3. If not properly aligned, there is little to know pathway for air around the backside of the cylinder.

I wish that little bump in the back of the cylinder was bigger and could let more air around the back.

[Shadrach]

19 minutes ago, Ragsf15e said:

I wish that little bump in the back of the cylinder was bigger and could let more air around the back.

Mine has a thin piece of baffle seal wedged between the cylinder and the baffle wall. Number 3 is still warmest, but warm for my set up in level flight is ~340°, but that’s only on hot days.

[Ragsf15e]

1 hour ago, Shadrach said:

Mine has a thin piece of baffle seal wedged between the cylinder and the baffle wall. Number 3 is still warmest, but warm for my set up in level flight is ~340°, but that’s only on hot days.

Yeah I read one of our threads on that.  It’s not overly hot so I haven’t tried it, but on really hot days in climb it’s between 380-400.  In cruise ((ROP) it’s ~370 so I don’t really worry about it.

A little more even airflow would be nice because my #1 can be at 290-300 while 3 is at 370.  I even swapped the probes once just to see if they were wrong, but no.  Baffles are newish and pretty good seal, maybe a little wrinkle behind #3 by the oil dipstick door, but I can usually smooth it out.

[Marauder]

Yeah I read one of our threads on that.  It’s not overly hot so I haven’t tried it, but on really hot days in climb it’s between 380-400.  In cruise ((ROP) it’s ~370 so I don’t really worry about it.
A little more even airflow would be nice because my #1 can be at 290-300 while 3 is at 370.  I even swapped the probes once just to see if they were wrong, but no.  Baffles are newish and pretty good seal, maybe a little wrinkle behind #3 by the oil dipstick door, but I can usually smooth it out.

That’s a huge difference between 1 &3. Are the cylinders the same age? When I see the difference between them, it usually pretty close.




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[Shadrach]

27 minutes ago, Ragsf15e said:

Yeah I read one of our threads on that.  It’s not overly hot so I haven’t tried it, but on really hot days in climb it’s between 380-400.  In cruise ((ROP) it’s ~370 so I don’t really worry about it.

A little more even airflow would be nice because my #1 can be at 290-300 while 3 is at 370.  I even swapped the probes once just to see if they were wrong, but no.  Baffles are newish and pretty good seal, maybe a little wrinkle behind #3 by the oil dipstick door, but I can usually smooth it out.

This was my impetus for tweaking. The two coolest jugs, #1 and #4 run 300° +/-10 in the summer and track pretty close together. It takes work to get them up to 300° in winter.  Prior to tweaking the delta in temp during climb between #1 (coolest) and #3 (hottest) was >60°, now it’s more like 35° and tracks so close to #2 in cruise that they trade places as hottest cyl depending on mixture setting.

[Shadrach]

15 minutes ago, Marauder said:

That’s a huge difference between 1 &3. Are the cylinders the same age? When I see the difference between them, it usually pretty close.




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That looks like a healthy running engine. Given the temps and fuel flow, I’m betting it’s timed to 20° BTDC.

[Marauder]

It is timed at 20° and it runs well.


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[Ragsf15e]

5 hours ago, Shadrach said:

This was my impetus for tweaking. The two coolest jugs, #1 and #4 run 300° +/-10 in the summer and track pretty close together. It takes work to get them up to 300° in winter.  Prior to tweaking the delta in temp during climb between #1 (coolest) and #3 (hottest) was >60°, now it’s more like 35° and tracks so close to #2 in cruise that they trade places as hottest cyl depending on mixture setting.

Yes, I probably have 65 degrees between 1-3. The cylinders are same type and age (relatively new).  I think it’s just the standard cooling issue on 3.

[Shadrach]

4 hours ago, Marauder said:

It is timed at 20° and it runs well.


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Have you ever heard Mike @201er  describe his experience going from 25° to 20° and then back to 25°?

[jaylw314]

7 hours ago, Shadrach said:

This was my impetus for tweaking. The two coolest jugs, #1 and #4 run 300° +/-10 in the summer and track pretty close together. It takes work to get them up to 300° in winter.  Prior to tweaking the delta in temp during climb between #1 (coolest) and #3 (hottest) was >60°, now it’s more like 35° and tracks so close to #2 in cruise that they trade places as hottest cyl depending on mixture setting.

LOL, #4 and #1 are my hottest cylinders.  Granted, they're all within 40degF of each other, and plenty cool, but it says a lot about the vagaries of any particular installation

Edit: I should also admit the #3 is a thermocouple ring sensor on the factory probe, so it might actually be 10-20 degF hotter?

Edited July 3, 2022 by jaylw314

[kortopates]

…
I should also admit the #3 is a thermocouple ring sensor on the factory probe, so it might actually be 10-20 degF hotter?

it could be significantly more if you don’t have the firesleeve in place allowing cooling air to hit it.


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[jaylw314]

38 minutes ago, kortopates said:

it could be significantly more if you don’t have the firesleeve in place allowing cooling air to hit it.


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I'll take a look next oil change, but it couldn't be any worse than the old spark plug gasket sensor before.  That was a good 75degF too cool.

 

[Shadrach]

On 7/2/2022 at 8:23 PM, jaylw314 said:

LOL, #4 and #1 are my hottest cylinders.  Granted, they're all within 40degF of each other, and plenty cool, but it says a lot about the vagaries of any particular installation

Edit: I should also admit the #3 is a thermocouple ring sensor on the factory probe, so it might actually be 10-20 degF hotter?

I think that like designs track pretty closely.  Your bird is 20 years newer. It has a different cowl with smaller intake openings, an oil cooler intake above cylinder #4 and 20° ignition timing. I would not expect it to mirror my installation. 

Edited August 5, 2023 by Shadrach

[Ragsf15e]

4 minutes ago, Shadrach said:

I think that like designs track pretty closely.  Your bird is 20 years newer. It has a different cowl with smaller intake openings, an oil cooler intake above cylinder #4 and 20° ignition timing. I would not expect it to mirror my installation. 

Are you using 25degrees?  How much hotter did the CHTs run when you switched to 25?

[Shadrach]

On 7/2/2022 at 10:38 PM, Ragsf15e said:

Are you using 25degrees?  How much hotter did the CHTs run when you switched to 25?

I never switched. Like yours, my bird was delivered from the factory with 25°. All IO360 A1As were delivered that way until some time in the 70s. My mags were once inadvertently timed to 20° by a mechanic. I noticed something was different but could not put my finger on it until I read read his log book entry. I had them advanced back to 25° ASAP. I’m sure it would run cooler if timed to 20° but it runs plenty cool as it is so there is no incentive to retard the timeimg.

Edited August 5, 2023 by Shadrach

[Marauder]

Have you ever heard Mike [mention=8223]201er[/mention]  describe his experience going from 25° to 20° and then back to 25°?

Nope. What happened?


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[Shadrach]

4 hours ago, Marauder said:

Nope. What happened?


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IIRC, he said that at 20° he lost a few hundred FPM in climb and in cruise was slower by 2-3krs ROP and 5Kts LOP.

[jaylw314]

11 hours ago, Shadrach said:

I think that like designs track pretty closely.  Your bird is 20 years newer. It has a different cowl with smaller intake openings, an oil cooler intake above cylinder #4 and 20° ignition timing. I would not expect it to mirror my installation. 

Oh wait, is the oil cooler in a different place on the F?  I didn't realize that

[Ragsf15e]

53 minutes ago, jaylw314 said:

Oh wait, is the oil cooler in a different place on the F?  I didn't realize that

Yes, the standard location on the F is in the front left of the lower cowling, right below the #2 cylinder.  Some people have an stc relocating it behind #4.  I also think the intake and cowling improved airflow significantly between the F/J.

[jaylw314]

9 minutes ago, Ragsf15e said:

Yes, the standard location on the F is in the front left of the lower cowling, right below the #2 cylinder.  Some people have an stc relocating it behind #4.  I also think the intake and cowling improved airflow significantly between the F/J.

oooohkay, yeah, that's REALLY different, I hadn't realized quite how different! 

[A64Pilot]

Increasing timing, you WILL increase HP, and should / may decrease BSFC some.

Increased HP WILL increase cyl head temp, and it WILL reduce detonation margin, on edit detonation is the limit for timing advance, hence modern automobiles have detonation sensors and will often run right at the limit of detonation. Cooling is also a limit of course.

Lycoming decreased timing because they learned they could still make the HP requirement and the engine ran cooler, and running cooler it would last longer. I don’t think you will find that in writing.

This is when the engine was operated IAW Lycoming recommendations, which is run pretty hard and either peak or ROP, don’t operate it that way and of course things may or may not change.

Ideal would be a timing switch so you could run 20 on takeoff and when climbing at TO power and a way to advance once in cruise, graduate level would be to do it based on manifold pressure.

I believe almost 100 years ago Buick figured this out and fitted a vacuum advance on their distributor that would advance timing when loads were low and significantly increase economy, our 1923 Model T your in charge of timing, the lever is under the steering wheel on the left side, retard to start, normal cruise full advance, hill climbing retard some or it will overheat.