Jump to content

High CHT


Recommended Posts

So I have a JPI EDM 700 engine monitor on my C model and I am seeing extremely high CHT on I know the #2 cylinder during climb out.  Around 450 degrees.  I climb at 26 squared and 120 mph.  I end up lowering the nose to bring the values down. This started last summer, then stoped over the winter and now it seems to be making another visit.  Any ideas? Wondering if it’s a probe problem or maybe baffling?

Link to comment
Share on other sites

11 minutes ago, wings_level said:

So I have a JPI EDM 700 engine monitor on my C model and I am seeing extremely high CHT on I know the #2 cylinder during climb out.  Around 450 degrees.  I climb at 26 squared and 120 mph.  I end up lowering the nose to bring the values down. This started last summer, then stoped over the winter and now it seems to be making another visit.  Any ideas? Wondering if it’s a probe problem or maybe baffling?

Aside from the single hot cylinder problem, don’t climb anything squared. Full power climb has been proven to be cooler and more effective.

  • Like 1
Link to comment
Share on other sites

While not quite as high, I'm fighting the same issue on #2.  Climbing at WOT, 2500, and 120 mph keeps mine under 400.  I was seeing 415-420 before.  I've looked at the baffles but probably not carefully enough.  Not happy about it, but living with it for the time being.  Good luck and please post if you end up finding the answer.

Link to comment
Share on other sites

As Don mentioned, probes are the starting point.  Do you have bayonet style or a spark plug gasket style?  Before anything else confirm that the indication is correct?  A leaking exhaust gasket can artificially raise CHT if it is aimed at the cylinder head or CHT probe.

Clarence

Edited by M20Doc
Link to comment
Share on other sites

I hear you and I feel your pain. Since I got my plane more than 10 years ago I have been battling high CHTs. I worked on every possible angle. Got a new doghouse, looked at the baffles, fuelhoses and pump to increase fuel flow, ignition to adjust timing, installed new ARI cowling and opened the cowlflaps.

From all these things what helped was to increase the fuel flow (I am up from 15.3 to 16.3) and adjusting the cowlflaps.

Of course technique also helped a lot. Let the plane accelerate until 120 mph and then push the nose up.

Overall I brought the CHTs down by 30 degrees and all are now acceptable with the exception of #3 that still rises to 450 during take off and initial climb.

I am now working on the carburetor as my last chance to get the issue resolved... otherwise I am out of ideas...

I am happy to share data and experiences if somebody needs and wants it. But please if you have any additional ideas please let me know.

Oscar




Sent from my iPhone using Tapatalk Pro

  • Like 1
Link to comment
Share on other sites

23 hours ago, MikeOH said:

While not quite as high, I'm fighting the same issue on #2.  Climbing at WOT, 2500, and 120 mph keeps mine under 400.  I was seeing 415-420 before.  I've looked at the baffles but probably not carefully enough.  Not happy about it, but living with it for the time being.  Good luck and please post if you end up finding the answer.

Yeah,

My ‘67F is similar… CHT #2 is the highest at 380+ and can touch 400F in the prolonged climb on a warmer PNW day, measured on EI CGR-30. I always climb WOT and full RPM at 120mph.

In cruse engine runs cool, all CHTs are low 300s with #2 being highest 330-340. At standard or cooler air temps and LOP, some CHTs are below 300.

On last annual my IA run a “Coke bottle flow test” and all injectors flow good and are clean. I have yet to swap #2 and #4 probes and check for that.

 

While baffle seals do not look bad, they are getting old and somewhat warn. No obvious tears or leaks but I think I might replace them on next Annual or during winter when I’ll fly less.

I’d be interested to hear about possible resolution of the issue.

Regards,

Link to comment
Share on other sites

23 hours ago, MikeOH said:

While not quite as high, I'm fighting the same issue on #2.  Climbing at WOT, 2500, and 120 mph keeps mine under 400.  I was seeing 415-420 before.  I've looked at the baffles but probably not carefully enough.  Not happy about it, but living with it for the time being.  Good luck and please post if you end up finding the answer.

My suggestion would be to shine a flashlight in the cowl and look for holes in the baffling..  you can easily do this if you take the top cowl off and then shine the light in the doghouse if your mooney has that setup.  If not maybe the oil door on the cowling

Link to comment
Share on other sites

Good news is that you have an excellent engine monitor to help exclude a number of things. 

  • The probes are likely fine but its worth a quick swap of #2 for #4 to make sure. 
  • Make sure you are getting somewhere close to 18gph FF at full power under standard conditions. It's probably not the issue, but it's trivial to look. The carb can be the culprit. 
  •  Make sure doghouse is as tight as you can get it. Plug every hole. I think mine is made of more RTV than aluminum at this point.  Change the baffle seals at the front if needed. The areas around the starter and alternator can be a real pain because the bottom cowl has to be dropped.
  • Consider all other possible high CHT reading causes, including induction leaks, mag timing, exhaust leaks blowing on the probe. The engine monitor can provide a lot of info in this regard.  You may have to delve into it yourself however, as some A&Ps are not versed in looking at this type of data.  Savvy has a paid service that will help analyze if you're not experienced at looking at this stuff.

It's worth a try climbing at WOT instead of 26-squared because pulling the throttle back disengages the carb enrichment circuit.  However this benefit of WOT is questionable in the minds of many C model owners including this one. I can't tell the difference in my subjective experience. Pulling back to 25-squared after getting away from the ground may run cooler. There was a nice discussion on another recent thread about the enrichment circuit and how it works, when it helps, and when it doesn't.

I saw 450 in climb for the first time this winter after looking at all these issues, but it was after a long ground run pending an IFR release on a training flight. If you can't keep temps below 350ish on the ground, you're gonna have problems early in climb regardless, particularly in the summer.

You may go through all this troubleshooting only to throw your hands up and accept that C models have a crappy cowl design that makes them run hot. My #2 is the problem child in cruise - always running 20-30 hotter in cruise than the rest and preventing me from leaning to best economy.  The fuel injected, angled valve brethren do much better with this issue across the board.  In my mind, the only C model owners who don't have CHT issues are the ones who don't have an engine monitor to detect them :lol:

  • Like 3
Link to comment
Share on other sites

On 4/1/2018 at 4:29 PM, Oscar Avalle said:

I hear you and I feel your pain. Since I got my plane more than 10 years ago I have been battling high CHTs. I worked on every possible angle. Got a new doghouse, looked at the baffles, fuelhoses and pump to increase fuel flow, ignition to adjust timing, installed new ARI cowling and opened the cowlflaps.

From all these things what helped was to increase the fuel flow (I am up from 15.3 to 16.3) and adjusting the cowlflaps.
 

Oscar - what was the exact setting change that you made to the cowl flaps, how much did it help in climb vs cruise, and did opening them affect your cruise speed?  I have the same fixed cowl flaps as you I think.  The OP may have adjustable flaps to open if he's pre '68.

Link to comment
Share on other sites

Oscar - what was the exact setting change that you made to the cowl flaps, how much did it help in climb vs cruise, and did opening them affect your cruise speed?  I have the same fixed cowl flaps as you I think.  The OP may have adjustable flaps to open if he's pre '68.

Actually interestingly my Mooney has movable cowl flaps. I always wondered why and how... in any event I can open them a bit more and it made a huge difference. I would say about 20 to 30 degrees.


Sent from my iPhone using Tapatalk Pro
  • Like 2
Link to comment
Share on other sites

I have an issue on #2 but figured it was a spark plug sensor vs. the bayonet plug because the factory installed probe is hogging the hole. I found out I had at least two easy options: move the spark plug thermocoupler to the top spark plug, or purchase a “piggy back” sensor that shares the location with the factory probe. The latter was on $100 from Spruce.

JPI EDM 700 as well.

Link to comment
Share on other sites

12 hours ago, Igor_U said:

Yeah,

My ‘67F is similar… CHT #2 is the highest at 380+ and can touch 400F in the prolonged climb on a warmer PNW day, measured on EI CGR-30. I always climb WOT and full RPM at 120mph.

In cruse engine runs cool, all CHTs are low 300s with #2 being highest 330-340. At standard or cooler air temps and LOP, some CHTs are below 300.

On last annual my IA run a “Coke bottle flow test” and all injectors flow good and are clean. I have yet to swap #2 and #4 probes and check for that.

 

While baffle seals do not look bad, they are getting old and somewhat warn. No obvious tears or leaks but I think I might replace them on next Annual or during winter when I’ll fly less.

I’d be interested to hear about possible resolution of the issue.

Regards,

Thanks for you post!

Your details are a mirror of mine: when running cruise LOP #2 runs 330-340, and I've occasionally seen under 300 on the others, although they are usually around 310.

I too, did the "Coke bottle test" with the same results; all flowed the same.  A&P cleaned the injectors, too.  But, made no difference.

A couple of posters have indicated adjusting fuel flow at WOT; I'm at about 16.5 gph...maybe that should be higher an injected engine?

I really need to try swapping probes...

Link to comment
Share on other sites

Same with my Mooney M20F from 1967:

My Mooney has the Lasar lower cowl enclosure installed and a Powerflow exhaust system. 

All CHTs are doing very fine. Except CHT2 during the climb. Shortly after takeoff my EDM930 shows CHT 2 rising   to about 380F. Then I  lower the nose and trade some of the climb rate for a speed of 110 to 120 KIAS to keep it at or below 380F. In Florida this is normally no problem due to no obstacles. Sometimes the engine monitor shows a temperature between 380 and 400 for about 2 minutes and then with the lowered nose,  CHT2 will go back to below 380F.  The other CHTs are about 30F less and  never hit 380F.

During cruise, I fly lean of peak and my CHT2 is the hottest, but always well below 380F. I usually see 320 to 340F for CHT2 and the others are 290 to 310F.

I will ask the shop to adjust the cowl flaps as follows: Open them more in the fully open position and keep the acual closed position or even close them more in the closed position. So the complete travel of the cowl flaps has to be extended.

Here are the datas from some of my last flights:

CHT2 below 380F:

https://www.savvyanalysis.com/flight/2377090/f2662206-c173-48b5-8853-f762d38a21e0

This flight departed after 15 minutes of taxitime with high grossweight (CHT2  was for 2 minutes above 380F):

https://www.savvyanalysis.com/flight/2377094/278e05d7-5212-4b39-984b-ca90a3245ebf

Link to comment
Share on other sites

On 2018-04-01 at 1:02 PM, wings_level said:

So I have a JPI EDM 700 engine monitor on my C model and I am seeing extremely high CHT on I know the #2 cylinder during climb out.  Around 450 degrees.  I climb at 26 squared and 120 mph.  I end up lowering the nose to bring the values down. This started last summer, then stoped over the winter and now it seems to be making another visit.  Any ideas? Wondering if it’s a probe problem or maybe baffling?

450F is well into the damaging temperature range.  As mentioned above, check the baffling, etc.

Keeping temperature down in the climb can also be helped by moving peak cylinder pressure to later in the power stroke.  Two ways to do that are: 1) keep your rpm high and 2) slow the mixture burn speed by keeping the mixture rich (and verify that the enrichment circuit is operating).  

Try WOT and 2700.

 

Edited by Cyril Gibb
Link to comment
Share on other sites

On ‎4‎/‎2‎/‎2018 at 8:49 PM, Bryan said:

I have an issue on #2 but figured it was a spark plug sensor vs. the bayonet plug because the factory installed probe is hogging the hole. I found out I had at least two easy options: move the spark plug thermocoupler to the top spark plug, or purchase a “piggy back” sensor that shares the location with the factory probe. The latter was on $100 from Spruce.

JPI EDM 700 as well.

The factory piggyback sensor seems to be more accurate, but still unsure how accurate.  I had a CHT that was wildly low (like 50-70 degF lower) than the other with a spark plug sensor.  When I switched to the piggyback, that CHT is now only about 20-30 degF lower, but still consistently so.  On the ground they all ready the same, so I don't really have a way to verify the temp in flight.

Link to comment
Share on other sites

So I have a JPI EDM 700 engine monitor on my C model and I am seeing extremely high CHT on I know the #2 cylinder during climb out.  Around 450 degrees.  I climb at 26 squared and 120 mph.  I end up lowering the nose to bring the values down. This started last summer, then stoped over the winter and now it seems to be making another visit.  Any ideas? Wondering if it’s a probe problem or maybe baffling?

What are the other cylinders showing?
Link to comment
Share on other sites

  • 2 weeks later...

So I'm not alone! Put in a JPI 830 and experience the same issue. Probe has been switched to no avail, the baffling is in good shape, timing checked and rechecked #2 RUNS TOO HOT! I back down when it reaches 400f although the owners manual says 500f is max. Run it full rich in the climb to let the gas cool it down oil psi is around 87 cowl flaps full open. Still not a fan of having MP higher than RPM. #2 runs hotter in cruse also. I wonder if it is an air burble behind prop on down side rotation?

Link to comment
Share on other sites

You may have left out...

Cruise climb at 120mphias...

There are airflow improvements for O360 cooling....

Cowl closure, doghouse improvements, and new cowling bits around here somewhere...

The old manual left out how important Airspeed is to cooling.  It didn’t tell the cost of running near the 500°F redline...

Without a full set of EGT sensors, you can’t tell how good your fuel distribution is or when you have improved it by moving the throttle butterfly plate...

PP thoughts,

-a-

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.