Abnormal CHT?

[par]

Gents,

here is a picture I took today on a flight back from NY. This is in a carbeurated C and as you guys can see, the #4 CHT is significantly higher than the rest. Usually, #2 and #4 are pretty well matched and #1 and #3 are 30-50 degrees lower. This is with the engine leaned of course. When full rich, #3 is the hotter cylinder with the other 3 relatively well matched.

So, what do you guys think I should do? I know the cylinder is not being harmed at that temperature but I would like it to better matched. 

Edited November 27, 2016 by par

[Mooneymite]

Check the baffling on the left side of the engine.

 

[par]

55 minutes ago, Mooneymite said:

Check the baffling on the left side of the engine.

 

My IA looked at all of this and made improvements just a year ago. What exactly am I looking for? This issue only exists when the engine is leaned out. Everything is well within limits during climbout on #4.

[Cruiser]

Does your M20C have cowl flaps? From what I hear some do and some don't.

Note that the cowl flaps are supposed to be adjusted so that they are open about 1 inch when the cowl flap control is in the closed position. This is per the maintenance manual.

[par]

It does and I keep mine open all the time. If I close the, all CHT's go up.

[Cruiser]

Ok then, when you lean which cylinder peaks first and which cylinder peak last?

[Hector]

I assume you have a doghouse like my C and I would definitely check to see that you have no leaks. Cover up any hole in the doghouse you can find and pay attention at any gaps around the starter and alternator. That being said I have a couple of questions. At 23 inches and 2440 rpm your JPI says you are making 63% horsepower? That seems low to me. You sure the %HP is adjusted correctly for a C in your JPI? Also what are you leaned to? At 8.4 GPH and that power setting I would think you are pretty close to peak? I typically operate at 65% power (22 inches and 2400 rpm) and leaned 20 degrees rich of peak my fuel flow is just a bit over 9 GPH at 7-9k feet. My temps are in the 360 range in cruise but during climb even at 120 mph they get up to 400. I have resigned myself that is normal for a C and do the best I can during climb.

[par]

16 hours ago, Hector said:

I assume you have a doghouse like my C and I would definitely check to see that you have no leaks. Cover up any hole in the doghouse you can find and pay attention at any gaps around the starter and alternator. That being said I have a couple of questions. At 23 inches and 2440 rpm your JPI says you are making 63% horsepower? That seems low to me. You sure the %HP is adjusted correctly for a C in your JPI? Also what are you leaned to? At 8.4 GPH and that power setting I would think you are pretty close to peak? I typically operate at 65% power (22 inches and 2400 rpm) and leaned 20 degrees rich of peak my fuel flow is just a bit over 9 GPH at 7-9k feet. My temps are in the 360 range in cruise but during climb even at 120 mph they get up to 400. I have resigned myself that is normal for a C and do the best I can during climb.

Yes, it is the factory setup for the doghouse (everything at right angles to optimize airflow, NOT). I will take a look for any holes during the upcoming annual but I did have my mechanic seal everything up last year the best he could.

I do not know if the HP rating is completely accurate but I never take it to be. I'll call JPI and go through the programming again to make sure it is set correctly. I can tell you that the fuel flow is reading a little lower than actual based on the last couple of fill-ups. After a full tank, the JPI reads 2-4 gallons lower than what I actually use. So, the fuel flow displayed is lower than reality. I normally lean the engine to the point of roughness and refine it from there, rather than leaning to peak. Also, much like your take-off's, my #3 is usually the troublemaker that breaks 400 easily on hot days. I can usually manage to keep it below 400 or thereabouts in winter weather. I don't lose too much sleep over it though because several people, to include D. Maxwell, have told me not to worry even if I'm looking at 430 during take off as long as it is cooling back down during cruise. Generally speaking, even on the hottest of days, #3 will come back down below 400 within 3-5 mins of taking off.

[Cyril Gibb]

It would be interesting to post a graph of your CHTs in relation to EGTs (GAMI spread) while you're leaning to see the peaking sequence.  Additionally try doing a test for induction leaks (from the Savvy site).  What's the fuel flow at full throttle?  If it's got one, is the carb enrichment function working?

People who know much more about engine management than me and have studied these things consider >400F to be very bad for cylinders with even a short period having cumulative damage.  Note that at 400F the tensile strength of your aluminum cylinder heads is 50% of that at room temperature.  The strength curve drops sharply more after that, so 430F should be of a concern.

[par]

28 minutes ago, Cyril Gibb said:

It would be interesting to post a graph of your CHTs in relation to EGTs (GAMI spread) while you're leaning to see the peaking sequence.  Additionally try doing a test for induction leaks (from the Savvy site).  What's the fuel flow at full throttle?  If it's got one, is the carb enrichment function working?

People who know much more about engine management than me and have studied these things consider >400F to be very bad for cylinders with even a short period having cumulative damage.  Note that at 400F the tensile strength of your aluminum cylinder heads is 50% of that at room temperature.  The strength curve drops sharply more after that, so 430F should be of a concern.

Fuel flow at T/O is over 18gph, which is normal. I'll download the data and take a look.

The temperature issue comes from Don Maxwell...not something I made up. I think its safe to assume he knows what he is talking about. I too have read all about how bad it is to see temps above 400 degrees but the only way that will happen in the heat is by taking off at a very low throttle setting. This plane had been around for well over 50 years and i'm sure this "problem" has always existed and yet here it is. A lot of things are still a mystery with these engines and it seems there is no clear answer or consensus on some topics.

[carusoam]

The good news is the EGTs are relatively close.  This means the heat being supplied to the cylinders is just about even.  Can they get a tighter spread using a carb?

The CHTs are not close.  One is 80°F away from the coldest.  It could be the airflow through that one cylinder's fins is being allowed to escape, or there is something not right about it's sensor.

Is that a ring shaped sensor sitting under a spark plug?  This is a way to introduce a 50°F gauge error.  It is OK for other planes like Brand C or P...

Mooney pilots put really nice JPI equipment on their carbed engines. They typically find a better sensor location to minimize this error type.  The ship's gauge is sitting in the well.  This CHT gauge is sitting somewhere else.

Best regards,

-a-

[Marauder]

Just a comment on your %HP and fuel discrepancy on fill ups. It looks you will need to adjust the HP constant and the k factor for the fuel flow. Both are useable settable and the procedure can be found in the operator's manual.

For the k factor, I would try to get a few trips in where you use at least 15 gallons on a flight. Just track how much you use versus what the 830 says it used. There is a nice formula in the book to recalculate the k factor. I have fine tuned mine that I am usually only off a few tenths of a gallon.




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[Oscar Avalle]

Yes, it is the factory setup for the doghouse (everything at right angles to optimize airflow, NOT). I will take a look for any holes during the upcoming annual but I did have my mechanic seal everything up last year the best he could.
I do not know if the HP rating is completely accurate but I never take it to be. I'll call JPI and go through the programming again to make sure it is set correctly. I can tell you that the fuel flow is reading a little lower than actual based on the last couple of fill-ups. After a full tank, the JPI reads 2-4 gallons lower than what I actually use. So, the fuel flow displayed is lower than reality. I normally lean the engine to the point of roughness and refine it from there, rather than leaning to peak. Also, much like your take-off's, my #3 is usually the troublemaker that breaks 400 easily on hot days. I can usually manage to keep it below 400 or thereabouts in winter weather. I don't lose too much sleep over it though because several people, to include D. Maxwell, have told me not to worry even if I'm looking at 430 during take off as long as it is cooling back down during cruise. Generally speaking, even on the hottest of days, #3 will come back down below 400 within 3-5 mins of taking off.

I had a long fight with my CHTs. They were high and did not come down. I got a new doghouse, carburetor, adjusted timing and got a new cowling. I am now down to your figures...so as long as they come down in cruise... they are fine.

I just got myself a JPI 900. How do you like yours?

Oscar


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[par]

On 12/22/2016 at 9:37 AM, Oscar Avalle said:

I had a long fight with my CHTs. They were high and did not come down. I got a new doghouse, carburetor, adjusted timing and got a new cowling. I am now down to your figures...so as long as they come down in cruise... they are fine.

I just got myself a JPI 900. How do you like yours?

Oscar


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 I think I'm finishing fighting the CHT issue. The plane is almost twice my age and seems to have done fine so far and I'm starting to think we often end up chasing ghosts with these mic century machinery. I'm just going to live with the high CHT's on TO as long compressions are good and nothing else is amiss.

the JPI is great and a must have in my opinion. This is especially important when we are dealing with engines that do not run to modern standards. The ability to monitor every aspect of the engine is vital for us. 

[Oscar Avalle]

Yes, I agree there are fights worth fighting until you get to a point were the result seems acceptable. That is where I am now. I know that my CHTs trend to be on the high side and I just manage it as well as I can. 

One www side that I use to upload my JPI data is www.savvyanalysis.com. It is much better and more intuitive than JPI software...

Oscar

[carusoam]

For ease of use...

https://www.savvyanalysis.com/home

we have an MS member that works there.  Very helpful.

Best regards,

-a-

[Oscar Avalle]

For ease of use...
https://www.savvyanalysis.com/home
we have an MS member that works there.  Very helpful.
Best regards,
-a-

Who?


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[cnoe]

Kortopates (Paul) at Savvy looks out for all us Mooney drivers (paid subscribers). He's been a big help to me with chasing down small anomalies, etc.


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[Oscar Avalle]

Kortopates (Paul) at Savvy looks out for all us Mooney drivers (paid subscribers). He's been a big help to me with chasing down small anomalies, etc.


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Indeed, I did not know that he was a dedicated Mooney guy! He helped me with my CHT issue! Great service


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