High CHT temps and Baffle seal M20C

[Heloman]

20 hours ago, Shadrach said:

I would say that "one" of the reasons to experience high CHT's in a 180hp Mooney is because of poorly maintained baffles. It's certainly not the only reason.  Anecdotally speaking I have to say that I see far more in the way of elevated CHT complaints about the carburetted birds than their injected brethren.  I believe that many of the carburetted birds run too lean at max power.  The fact that they heat up so quickly tends to indicate a mixture issue to my way of thinking.  The fact that many are seeing CHTs near 400df or more on initial climb out suggests they are building heat rapidly during the takeoff run.  Even when a piece of baffle seal had detached, my F never saw anything like that. I would have to hang it on the prop on a hot day for quite a while to build the kind of heat that many of my carburetted friends are seeing during initial climb and long before reaching so much as pattern altitude.

I've also been trying to get takeoff temps under control in my C, all the regular things have helped incrementally, and this has become my theory as well. One thing I've noticed is when I takeoff full rich and start seeing high temps, I tend to start turning my mixture in out of habit, I'll immediately see EGTs come down a little . I've checked to be sure the mixture arm on the carburetor is fully on its stop when I push the mixture in normally and it is, it seems putting pressure on it by screwing it in a little is enough to add just a little more fuel; makes me think temps would be allot better if I could keep going with more fuel. I do have a powerflow and I talked with them about this issue because I've heard some people have had to make carb adjustments, they're adamant that I don't have this issue as long as I get the little RPM rise when the mixture's pulled on shut down. But I don't really believe Idle mixture has anything to do with it.

Edited October 4, 2017 by Heloman

[DXB]

52 minutes ago, Heloman said:

 I do have a powerflow and I talked with them about this issue because I've heard some people have had to make carb adjustments, they're adamant that I don't have this issue as long as I get the little RPM rise when the mixture's pulled on shut down. But I don't really believe Idle mixture has anything to do with it.

Yeah the idle mixture is irrelevant here - disappointingly, what the Powerflow people are saying is hogwash.  Just make sure you have the richer carb model # or the leaner one that's been modified - I forget the #s but I've posted on here somewhere before when I was trying to figure out the same, and ideally are getting fuel flows >17gph on takeoff at lower DAs if you have the instrumentation.  

As for the folks saying that meticulously sealing the doghouse is enough to control temps on the O-360 even in hot climates, I'm not doubting their experience, but I certainly do not share it. I've expended a couple years of very close attention to baffle rehab (and $$) with limited improvement. In summer, I've learned to live with temps initially hitting 420s on 2-3 cylinders during climbout at 110-120mph.   

What's more frustrating is that #2 always runs 30 degrees hotter than the others in cruise, often forcing me to burn an extra gph just to keep it in the 380s. No induction leak to explain it. Clearly there's a special airflow problem around my #2 - the rest do great in cruise.   My physics and engineering knowledge is clearly inadequate to figure out why this is the case, as is that of most A&Ps. I would love for a real expert in airflow dynamics to take a look sometime.  i suspect it just needs a small tweak to make a big difference.

[Shadrach]

55 minutes ago, DXB said:

Yeah the idle mixture is irrelevant here - disappointingly, what the Powerflow people are saying is hogwash.  Just make sure you have the richer carb model # or the leaner one that's been modified - I forget the #s but I've posted on here somewhere before when I was trying to figure out the same, and ideally are getting fuel flows >17gph on takeoff at lower DAs if you have the instrumentation.  

As for the folks saying that meticulously sealing the doghouse is enough to control temps on the O-360 even in hot climates, I'm not doubting their experience, but I certainly do not share it. I've expended a couple years of very close attention to baffle rehab (and $$) with limited improvement. In summer, I've learned to live with temps initially hitting 420s on 2-3 cylinders during climbout at 110-120mph.   

What's more frustrating is that #2 always runs 30 degrees hotter than the others in cruise, often forcing me to burn an extra gph just to keep it in the 380s. No induction leak to explain it. Clearly there's a special airflow problem around my #2 - the rest do great in cruise.   My physics and engineering knowledge is clearly inadequate to figure out why this is the case, as is that of most A&Ps. I would love for a real expert in airflow dynamics to take a look sometime.  i suspect it just needs a small tweak to make a big difference.

Dev,

Three thoughts:

1) Have you ever evaluated the mixture setting on #2 in cruise?  If #2 CHT is 405 and everthing else is <380 how far is #2 EGT from its peak?  

2) Have you ever added a touch of carb heat after leaning in cruise?

3) I theorize that the carburetted birds were certified before buyer much cared about or knew what was optimal and were willing to settle for adequate.  Folks used to be perfectly happy using a single cylinder as an proxy for what the other three or five or seven (for Clarence) we're doing.  1gph for every 10hp is a nice goal to shoot for in an injected engine where that fuel is evenly divided amoung all cylinders.  In a carbed engine, it's conceivable that more margin would be ideal to to ensure the leanest (hottest) get's adequate fuel.

[DXB]

42 minutes ago, Shadrach said:

Dev,

Three thoughts:

1) Have you ever evaluated the mixture setting on #2 in cruise?  If #2 CHT is 405 and everthing else is <380 how far is #2 EGT from its peak?  

2) Have you ever added a touch of carb heat after leaning in cruise?

3) I theorize that the carburetted birds were certified before buyer much cared about or knew what was optimal and were willing to settle for adequate.  Folks used to be perfectly happy using a single cylinder as an proxy for what the other three or five or seven (for Clarence) we're doing.  1gph for every 10hp is a nice goal to shoot for in an injected engine where that fuel is evenly divided amoung all cylinders.  In a carbed engine, it's conceivable that more margin would be ideal to to ensure the leanest (hottest) get's adequate fuel.

Thanks Ross certainly relevant points.

1) Yes I've experimented considerably with mixture vs EGTs.  #2 never peaks first or even second if I insist on leaning  aggressively as possible.  Right now I can't run more than one cylinder LOP  (max by 15 degrees) without roughness, and #2's CHTs won't let me go that far even, so I know in current use #2 is running well ROP even as I struggle to limit temps to 380s.   

2) I've heard this can help the mixture distribution and continue to do it, but it makes no obvious difference for me -   nor does pulling the throttle out slightly to angle the plate when running wide open.

3) I agree completely. My fuel flows always run in the 17-18gph range at takeoff and I have the richer carb, so may not be much room for improvement there.  In  the old days, I would have had  a single EGT, and CHT  on #3 only.  I would likely be happy as a clam with my temps in cruise and routinely lean to about 9.5gph at WOT/2500rpm/7500ft - the leanest I can go before it turns rough. Then one fine day my #2 exhaust valve would snap off and create a lot of drama. 

But as a denizen of the modern world, I installed a JPI900 after buying the bird 3 years ago, which forces me run at about 10.5 gph while fidgeting with the mixture knob to keep  #2 temps in the 380s.  And I borescope my own cylinders 2x/year, which has led to IRANs of 2 cylinders (#1, #2) for burnt exhaust valves, likely from damage from previous owner who didn't have a monitor.  I really think it's a crappy cowl/baffle design.  Someone with an engineering background should fix it.  I would pay $$.

[Shadrach]

6 minutes ago, DXB said:

Thanks Ross certainly relevant points.

1) Yes I've experimented considerably with mixture vs EGTs.  #2 never peaks first or even second if I insist on leaning  aggressively as possible.  Right now I can't run more than one cylinder LOP  (max by 15 degrees) without roughness, and #2's CHTs won't let me go that far even, so I know in current use #2 is running well ROP even as a struggle to limit temps to 380s.   

2) I've heard this can help the mixture distribution and continue to do it, but it makes no obvious difference for me -   nor does pulling the throttle out slightly to angle the plate when running wide open.

3) I agree completely. My fuel flows always run in the 17-18gph at takeoff and I have the richer carb, so may not be much room for improvement there.  In in the old days, I would have had  a single EGT, and CHT  on #3 only.  I would likely be happy as a clam with my temps in cruise and routinely lean to about 9.5gph at WOT/2500rpm/7500ft - the leanest I can go before it turns rough. Then one fine day my #2 exhaust valve would snap off and create a lot of drama. 

But as a denizen of the modern world, I installed a JPI900 after buying the bird 3 years ago, which forces me run at about 10.5 gph while fidgeting with the mixture knob to keep  #2 temps in the 380s.  And I borescope my own cylinders 2x/year, which has led to IRANs of 2 cylinders (#1, #2) for burnt exhaust valves, likely from damage from previous owner who didn't have a monitor.  I really think it's a crappy cowl/baffle design.  Someone with an engineering background should fix it.  I would pay $$.

There are E models with the dog house as well, but I don't get the sense that CHTs are as much of an issue.  I have made very minor and non structural changes to a section baffle seal that made a significant difference to #3.  Without seeing your engine, it's hard to say why #2 is so troublesome.  My guess is that having the "short fins" faced forward and sheet metal covering a fair amount of the front of the cylinder is preventing a large section of that cylinder from getting any cooling air.  The Lancair guys have a similar issue with Continental applications and they cut an elongated oval in front of the cylinder.

[HRM]

11 hours ago, DXB said:

What's more frustrating is that #2 always runs 30 degrees hotter than the others in cruise, often forcing me to burn an extra gph just to keep it in the 380s. No induction leak to explain it. Clearly there's a special airflow problem around my #2 - the rest do great in cruise. 

Same on my E. Just baffling.

[Shadrach]

17 hours ago, DXB said:

Thanks Ross certainly relevant points.

1) Yes I've experimented considerably with mixture vs EGTs.  #2 never peaks first or even second if I insist on leaning  aggressively as possible.  Right now I can't run more than one cylinder LOP  (max by 15 degrees) without roughness, and #2's CHTs won't let me go that far even, so I know in current use #2 is running well ROP even as I struggle to limit temps to 380s.   

I've been thinking about this and it doesn't quite answer my question or completely rule out a mixture issue. 

It's conceivable that being 3rd to peak puts it right in the red box depending on the spread. A leaned scenario like the example below is what I'd like to rule out.

leaned in cruise to rough and enrichened until smooth

1st to peak leaned to 10 LOP 

2nd to peak leaned to 10 ROP

3rd to peak (#2) leaned to 50 ROP

4th to peak leaned to 90 ROP

This would indeed put #2 in the hottest mixture range.

I'm not suggesting that the baffle seal design isn't a problem, but it'd be good to know to what degree (bad pun). The only way to do this is to verify the actual value on that cylinder. For the purpose of this discussion  #2 is for all intents and purposes a single cylinder engine to be leaned relative to it's own peak. Does it run at acceptable temps leaned to 100ROP, 125ROP? What is the hot and cool (if there is one) mixture range for this cylinder relative to its own peak EGT. 

[Shadrach]

Harley's experience bolsters the idea that it's a baffle seal design flaw. Is there a way to temporarily remove the sheet metal in front of #2 without perminantly altering the doghouse?

Edited October 5, 2017 by Shadrach

[DXB]

1 hour ago, Shadrach said:

I've been thinking about this and it doesn't quite answer my question or completely rule out a mixture issue. 

It's conceivable that being 3rd to peak puts it right in the red box depending on the spread. A leaned scenario like the example below is what I'd like to rule out.

leaned in cruise to rough and enrichened until smooth

1st to peak leaned to 10 LOP 

2nd to peak leaned to 10 ROP

3rd to peak (#2) leaned to 50 ROP

4th to peak leaned to 90 ROP

This would indeed put #2 in the hottest mixture range.

I'm not suggesting that the baffle seal design isn't a problem, but it'd be good to know to what degree (bad pun). The only way to do this is to verify the actual value on that cylinder. For the purpose of this discussion  #2 is for all intents and purposes a single cylinder engine to be leaned relative to it's own peak. Does it run at acceptable temps leaned to 100ROP, 125ROP? What is the hot and cool (if there is one) mixture range for this cylinder relative to its own peak EGT. 

The scenario you describe is plausible- I could be putting #2 closest to the red box when I lean.  What argues against that being the dominant determinant of CHT here is that #2 CHT is hottest by far in every single power and mixture setting I've ever used in cruise, even at full rich - so the issue seems very intrinsic to the airflow to me.  Interestingly the situation is more variable in climb, with #3 usually being hottest.  I have no clue why -maybe something with the higher AOA altering how the air interfaces with the cowl.  

[HRM]

8 minutes ago, DXB said:

The scenario you describe is plausible- I could be putting #2 closest to the red box when I lean.  What argues against that being the dominant determinant of CHT here is that #2 CHT is hottest by far in every single power and mixture setting I've ever used in cruise, even at full rich - so the issue seems very intrinsic to the airflow to me.  Interestingly the situation is more variable in climb, with #3 usually being hottest.  I have no clue why -maybe something with the higher AOA altering how the air interfaces with the cowl.  

This now has me thinking that my oil issue (pushrod tube on exhaust) may have been detonation on #2.

[paulsmeds]

HRM, did you ever figure out why #2 is hotter? I'm having this exact problem.  I recently did a complete top overhaul and added a JPI engine monitor. I’m consistently showing #2 is much hotter than the rest. Climb will easily hit 400 while the next hottest is 350 as I lower the nose to keep it under 400 all full rich. Cruise 360ish while others low 300’s all while 40 degrees out. I’ve swapped sensors and verified sensors are good, checked for exhaust leaks blowing on the sensor and have the baffling in good shape.  Even on the ground just taxing #2 will be 50 degrees or more hotter than the rest.  I’m assuming this issue is there is no airflow pushing down past the fins on #2.

Interesting I had a small oil leak in the front seal and after a long flight, there would be oil up under the top cowl above #2 and was slowly wicking forward, up and out while totally dry above #1.  Suggests the airflow is not coming in past #2 but maybe stagnant due to back pressure on the pilot side.  #4 is also the next warmest (although okay) which also suggest I'm not getting much cooling air pushing down past #2 and #4.

I almost feel like there should be a baffle above #2 that deflects air down and keep it from blowing back out the front of the cowling.

Very interested if you made any progress in getting #2 cooler. We have some hot weather coming and I don’t want to bake these overhauled cylinders.

1967 Mooney M20F

IO360A1A

[SheryLoewen]

Its necessary to keep the baffle seal tight to keep high pressure on he top of the cylinders.

 Side note: The LASAR cowl closure does give speed increase 5 MPH in cruise and much more in decent. Usually it doesn't affect cooling. Completely removing the entire cowl gives complete access.

Paul

[carusoam]

8 hours ago, paulsmeds said:

HRM, did you ever figure out why #2 is hotter? I'm having this exact problem.  I recently did a complete top overhaul and added a JPI engine monitor. I’m consistently showing #2 is much hotter than the rest. Climb will easily hit 400 while the next hottest is 350 as I lower the nose to keep it under 400 all full rich. Cruise 360ish while others low 300’s all while 40 degrees out. I’ve swapped sensors and verified sensors are good, checked for exhaust leaks blowing on the sensor and have the baffling in good shape.  Even on the ground just taxing #2 will be 50 degrees or more hotter than the rest.  I’m assuming this issue is there is no airflow pushing down past the fins on #2.

Interesting I had a small oil leak in the front seal and after a long flight, there would be oil up under the top cowl above #2 and was slowly wicking forward, up and out while totally dry above #1.  Suggests the airflow is not coming in past #2 but maybe stagnant due to back pressure on the pilot side.  #4 is also the next warmest (although okay) which also suggest I'm not getting much cooling air pushing down past #2 and #4.

I almost feel like there should be a baffle above #2 that deflects air down and keep it from blowing back out the front of the cowling.

Very interested if you made any progress in getting #2 cooler. We have some hot weather coming and I don’t want to bake these overhauled cylinders.

1967 Mooney M20F

IO360A1A

Let’s invite @HRM to stop by…

Its been a few months since we have seen him…

Best regards,

-a-

[Greg Ellis]

6 hours ago, carusoam said:

Let’s invite @HRM to stop by…

Its been a few months since we have seen him…

Best regards,

-a-

Harley sold his Mooney quite some time ago, retired and bought an Ekolat.  I think he dropped off the Mooney world when he sold his.

[HRM]

16 hours ago, paulsmeds said:

HRM, did you ever figure out why #2 is hotter?

It was baffling, in more ways than one 

The ol' doghouse (once a Mooniac, always a Mooniac) had just gotten so raggedy it was leaking. We tightened things up and temps improved, slightly. I found that if I didn't push the initial climb like a drag racer, which I dearly loved to do, I could keep the temps down.

Also, I did not run into high temps until I installed my EI MVP50. I think that cylinder always heated up, I just didn't know it until new technology revealed it.

Good luck, just back off the throttle a bit (I know, hard to do in a Mooney).

[Greg Ellis]

Glad to see Harley still lurks!!!!

[Shadrach]

16 hours ago, paulsmeds said:

HRM, did you ever figure out why #2 is hotter? I'm having this exact problem.  I recently did a complete top overhaul and added a JPI engine monitor. I’m consistently showing #2 is much hotter than the rest. Climb will easily hit 400 while the next hottest is 350 as I lower the nose to keep it under 400 all full rich. Cruise 360ish while others low 300’s all while 40 degrees out. I’ve swapped sensors and verified sensors are good, checked for exhaust leaks blowing on the sensor and have the baffling in good shape.  Even on the ground just taxing #2 will be 50 degrees or more hotter than the rest.  I’m assuming this issue is there is no airflow pushing down past the fins on #2.

Interesting I had a small oil leak in the front seal and after a long flight, there would be oil up under the top cowl above #2 and was slowly wicking forward, up and out while totally dry above #1.  Suggests the airflow is not coming in past #2 but maybe stagnant due to back pressure on the pilot side.  #4 is also the next warmest (although okay) which also suggest I'm not getting much cooling air pushing down past #2 and #4.

I almost feel like there should be a baffle above #2 that deflects air down and keep it from blowing back out the front of the cowling.

Very interested if you made any progress in getting #2 cooler. We have some hot weather coming and I don’t want to bake these overhauled cylinders.

1967 Mooney M20F

IO360A1A

You have a 67F.  It should not have a doghouse.  Your baffle seal system differs from Harley's previous E model which has a doghouse.   

Number 3 is typically the hot cylinder for F models. It will be a challenge to diagnose a hot cylinder without EGT/CHT data.

[HRM]

1 hour ago, Greg Ellis said:

Glad to see Harley still lurks!!!!

 

[HRM]

1 hour ago, Shadrach said:

You have a 67F.  It should not have a doghouse.

I wasn't sure, but there you have it. Just baffling!