Poll on individual CHTs in carb'd planes

[DXB]

I'm asking because I'm puzzling why my #2 consistently runs 30 degrees hotter in cruise than everything else.  All my other temps are great, but #2 will make me waste 1-2gph and presumably also increase lead deposits because I often can't keep it under 390 otherwise!  Takeoff fuel flow is just fine. Timing is fine. Oil temps are perfect. No exhaust leak blowing on a probe. So it's gotta be the baffle! I just IRAN'd #2 (burnt exhaust valve - no mystery why in this scenario), then sealed up the front baffle around it very carefully.  I've finished breaking it in, and now the engine behaves EXACTLY the same as before the work was done.  Importantly #2 is never my leanest - it's usually #3, which I can at peak or 10 degrees lean of peak just fine, but doing that leaves #2 just rich of stoichiometric, with its CHT shooting past 400 in warm conditions.  BTW this is read off a EDM900 primary gauge with all the probes in the factory slot, so I'm convinced it's accurate. And #2 also seemed to be the problem child on the old EI monitor that my EDM900 replaced.

All this leaves me feeling like what is going on is intrinsic to the doghouse design and not a defect in mine or an idiosyncrasy of my carb'd engine's mixture distribution.  But then the factory probe is generally on #3 per my understanding.  I'm curious if other people's experiences would support this hypothesis - hence the survey.  

[Oscar Avalle]

Welcome to the club! There are several threads on this issue. What surprises me is that your #2 CHT is the hottest one. Normally #3 is the one that is acting up. I personally did everything I could to keep the CHTs low, I was able to reduce them a bit, but I know that I have to manage them to keep them in line around 380 to 400.


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[Marauder]

Dev - a couple of things to consider. If you upgraded to a 900, did you re-use the probes from another JPI? In my case I did. If you did, I would swap the CHT probe with another and see if you get the same thing. The probes can be non-linear and this may be the problem.

Also, how does the EGT on that cylinder compare to the rest? Has any worked been done on the induction system?


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[DXB]

44 minutes ago, Marauder said:

Dev - a couple of things to consider. If you upgraded to a 900, did you re-use the probes from another JPI? In my case I did. If you did, I would swap the CHT probe with another and see if you get the same thing. The probes can be non-linear and this may be the problem.

Also, how does the EGT on that cylinder compare to the rest? Has any worked been done on the induction system?


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Thanks Chris - actually all new probes for the JPI, with #2 temps in complete agreement with the primitive old EI monitor I had. Induction system seems fine now - oddly when the cylinder work was done, the A&P found that all 4 intake tubes were from the wrong engine model (an O-320) and replaced them with correct ones. So everything past the carb has been snugged up recently, and doing this made zero difference in CHTs after the break in period. EGTs on #2 peak in cruise the mid-high 1400s, like on #3. 

[Hank]

Check your doghouse closely--how well do the top plates seal to the rest when put together? What shape is the baffling in at the rear of the doghouse? I spent two annuals resuscitating my doghouse, and went from LOP unable [despite playing with throttle position and variable carb heat] to being able to run >25º LOP without even playing with carb heat. But I only have the single factory gage, so I cant' contribute meaningfully to that part.

There are numerous threads here about doghouse issues--search and there are many posted photos, including my own before and after shots.

Good luck!

[Shadrach]

 

Hi Dev,

Sorry to learn that you're still sorting through this. If you are absolutely, positively sure that there is no intake leak causing this cylinder to run leaner, then it must be a baffle issue.   If it were me, I'd consider affixing temp test strips to the barrel and head. This should enable you to see where the greatest amount of heat is accumulating so you can start working the baffling to ensure air flow is reaching the affected area.

 

https://www.grainger.com/category/temperature-test-strips/temperature-and-humidity-measuring/test-instruments/ecatalog/N-bf1?refineSearchString=350&searchString=Temperature%2BTest%2BStrips&ts_optout=true#nav=%2Fcategory%2Ftemperature-test-strips%2Ftemperature-and-humidity-measuring%2Ftest-instruments%2Fecatalog%2FN-bf1Z1z061k0Z1z061k4Z1z061ku%2FNtt-350%3F_%3D1488313826706%26sst%3DAll%26ts_optout%3Dtrue

 

 

 

 

[jamesm]

I would be more interested in in the climb out phase CHT results .... My  2 hottest Cylinder   are  usually Cylinder #2 and Cylinder #4 in can happen in winter or any other season.

I haven't paid  too close attention  in the cruise phase of flight lately.  Is there data mining  software out there where you upload your data in CSV format ? I wonder what difference would be among CHT temps engine monitors for the same or similar  flight profile

Unfortunately  most of us are unable to experiment to see  what can do to fix a "certified /FAA approved problem"  without going through mound of paper work which should fixed be before the airplane were delivered.  I am hopping that FAR part 23 re-write and other FAA changes will allow us to at least investigate and make minor changes to the Type Certificate for evaluation purposes. So if we have the data test set  before  the changes and the data  test set after the changes that could be used as approval for minor changes/alteration for things CHT cooling on climb out , fuel tank sending units. flap position indicators, stab trim position indicators and other changes . Without cost being so high.  

James '67C

[DXB]

7 hours ago, Shadrach said:

 

Hi Dev,

Sorry to learn that you're still sorting through this. If you are absolutely, positively sure that there is no intake leak causing this cylinder to be run leaner then it must be a baffle issue.   If it were me, I'd consider affixing temp test strips to the barrel and head. This should enable you to see where the greatest amount of heat is accumulating so you can start working the baffling to ensure air flow is reaching the affected area.

 

https://www.grainger.com/category/temperature-test-strips/temperature-and-humidity-measuring/test-instruments/ecatalog/N-bf1?refineSearchString=350&searchString=Temperature%2BTest%2BStrips&ts_optout=true#nav=%2Fcategory%2Ftemperature-test-strips%2Ftemperature-and-humidity-measuring%2Ftest-instruments%2Fecatalog%2FN-bf1Z1z061k0Z1z061k4Z1z061ku%2FNtt-350%3F_%3D1488313826706%26sst%3DAll%26ts_optout%3Dtrue

 

 

 

 

Thanks that looks like an interesting idea -  there's just something thats peculiar about the airflow in my doghouse that wants to make #2 hot alone. I can't imagine its an intake leak because (1) it never peaks first upon leaning (2) it acts the same whether cruising down low at 23-squared or high at 2500/WOT.  Hopefully my reasoning is ok there?

[Shadrach]

36 minutes ago, DXB said:

Thanks that looks like an interesting idea -  there's just something thats peculiar about the airflow in my doghouse that wants to make #2 hot alone. I can't imagine its an intake leak because (1) it never peaks first upon leaning (2) it acts the same whether cruising down low at 23-squared or high at 2500/WOT.  Hopefully my reasoning is ok there?

Seems like sound reasoning. Do they typically peak in the same order? The internal baffling between cylinder #2 and #4 would be a good place to start. 

[tigers2007]

I want to amend my vote from just #2 to #2 and #4

[Shadrach]

1 minute ago, tigers2007 said:

I want to amend my vote from just #2 to #2 and #4

I think most C and G owners would be envious of those temps

[Ned Gravel]

27 minutes ago, Shadrach said:

I think most C and G owners would be envious of those temps

I cannot respond to the poll because I fly an E model, but I get temps like that too.  Clarence rebuilt my doghouse and it makes a big difference from what I was getting before.

[Shadrach]

Just now, Ned Gravel said:

I cannot respond to the poll because I fly an E model, but I get temps like that too.  Clarence rebuilt my doghouse and it is makes a big difference from what I was getting before.

I fly an F that has no dog house but my CHTs range between 285-330 in cruise.

[neonbjb]

Count me as another guy having issues with the #2 and #4 bank. For the other guys who have the issue - do you have the cowl enclosure mod?

 

Cylinders #1 and #3 are on a slightly higher plane than #2 and #4, I wonder if the cowl enclosure is blanking some of the airflow that was intended to flow over these cylinders. If this was the case the fuel injected guys would be seeing the same thing though.

Edited March 2, 2017 by neonbjb

[DXB]

15 minutes ago, neonbjb said:

Count me as another guy having issues with the #2 and #4 bank. For the other guys who have the issue - do you have the cowl enclosure mod?

 

Cylinders #1 and #3 are on a slightly higher plane than #2 and #4, I wonder if the cowl enclosure is blanking some of the airflow that was intended to flow over these cylinders. If this was the case the fuel injected guys would be seeing the same thing though.

That is truly an interesting idea.  I do have the cowl enclosure.  

[Hank]

2 hours ago, DXB said:

That is truly an interesting idea.  I do have the cowl enclosure.  

Planes with the original guppy mouth have reverse airflow coming out the guppy mouth instead of going in, so that's not a good option. Restricting the opening was easier than enlarging the exit area, but maybe you could create some data and convince your FSDO to sign off on double- or triple-sized flaps

[DXB]

So the limited poll results at least suggest that some other folks have #2 run hot in cruise, primarily due to airflow and not mixture distribution.  For most others it's #3.  My #3 is second hottest and the leanest, but runs 30 degrees cooler than 2.  At the same time 1&4 rarely, if ever, seem to be a problem for folks in cruise.  My #4 runs very cool.  

So I'm wondering if there's a way to adjust the doghouse to send more airflow over #2 rather than #4.  I wonder if #2 is the stasis point in the pressure gradient where flow is prone to reverse. Unfortunately I've no clue what I'm talking about.  I need an engineer.

[Andy95W]

1 hour ago, DXB said:

So I'm wondering if there's a way to adjust the doghouse to send more airflow over #2 rather than #4.  I wonder if #2 is the stasis point in the pressure gradient where flow is prone to reverse. Unfortunately I've no clue what I'm talking about.  I need an engineer.

Dev- no, there is not an adjustment to the doghouse, just patching holes.

And it really isn't about airflow, but about air pressure.  High pressure inside the doghouse, low pressure below it and the air moves through the cooling fins to equalize it and be ejected out of the cowl flap area.  If there are leaks, you decrease the high pressure and increase the low pressure, so less air moves through the fins.  

2 & 4 being hotter than 1&3 is not uncommon, due to the "pulse" of air from the downward moving prop blade on the 1&3 side of the engine.  This means higher pressure on that side and slightly lower pressure on the left side.

Perhaps you could add an internal baffle to direct some of that higher pressure to the left side of the engine- but it could be an exercise in futility and add different problems.

[Shadrach]

Andy,

Are you saying that there is no potential for turbulence and or stagnation within the plenum?  I am asking because I don't know.  It seem if that were the case, there would be no need for any internal baffling.

[Andy95W]

Uh... probably?

[Andy95W]

I do think in the case of the doghouse, part of the issue is the inverted-v design of the top that tends to focus the air pressure on the right side of the engine (1&3), along with the downward prop blade movement on that side. 

Beyond that, I'm guessing.

[Guest]

You might consider removing the Lycoming inner cylinder baffle and trimming 1/4"-1/2" off the side with the hottest cylinder.

Clarence

[Supercop0184]

Holy moly I NEVER SEE ANY TEMPERATURES below 350 even in CRUISE


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[par]

I took a picture yesterday at 4500' on a relatively cool day. Keep in mind this picture shows the power pulled back to maintain 75% or less to lean out the engine. I find the ROT to lean once above 3000' without reducing throttle to be highly inaccurate. This is especially true in the winter on a nice cool day.

 

 

[bonal]

174 oil temp that's really cool but at 23 degrees OAT probably helps quite a bit. I run about 200 on a 40 degree day. I wonder though how one can cook the water (condensation) out of the oil if you run that cool.