High CHT temp on #6

[Casey]

Ok so lately my #6 CHT has been running about 12 to 15 degrees hotter than the rest of the cylinders. In order for me to keep #6 under 400 degrees I have to keep the cowl flaps about 1/2 way open. Has anyone else had this problem? IVestas always been told if you run a cylinder over 400 you're doing damage to it. I have ano 89 bravo for what it's worth. Any ideas what could cause it? I'm going to run up to the airport and pull the cowling off today and see if there is something that could be ubstructing the airflow but I just had it off for an oil change and didn't notice anything. I was having the problem before the oil change so it's nothing I did durring that process. Also the EGT for that cylinder is the same as the rest so the fuel burn seems to be the same.

[Brian Scranton]

Three things I did to help correct my high CHT problem last week: fixed the baffles (they were bent and not directing airflow correctly, plugged a random old hose hole that was no longer in use and I cleaned and gapped my plugs, which made the engine run SO much smoother). Hope this helps! 

[Casey]

Thanks I'll take a closer look at the baffles tonight but I don't think I'll have time to do the plugs. 

[moxfox]

Here a chart for you to look at, this my help??

[kevinw]

Interesting you should post this. I was flying over the weekend in my J and I have a similar issue. The #4 cylinder in my A3B6 is always running hotter than the others. I thought of baffles also but I'm replacing my plugs with Tempest fine wire in the next week so I'm hoping that takes care of some of it. I talked to a mechanic about it and suggested switching CHT probes but he didn't think the difference was enough to warrant that. I've read not to let the temps get above 380df so 371 is starting to make me nervous.

[carqwik]

My #6 runs hotter than the rest by about 20-30 degrees.  In the summer, I just keep the cowl flaps open a little bit to keep it under 400 degrees.

[LANCECASPER]

I just ordered a set of new pre-cut baffle seals from GEE-BEE. On the last oil change a MSC had not laid the baffle seal correctly before cowling up the airplane - it was running hotter than usual. I discovered that before my annual and ordered a set. The material that GEE-BEE uses will make it much easier to make sure they are leaning forward when the cowl is put back. Anxious to finish up the annual so I can see what difference it made.

http://www.n252q.com/2007/09/baffled-about-baffling.html

[LANCECASPER]

The old ones were in rough shape.

Here's one piece - Old Baffle Seal and New Baffle Seal

My temps weren't bad but looking forward what kind of difference this makes.

[DVA]

On 8/1/2016 at 0:30 PM, Casey said:

Ok so lately my #6 CHT has been running about 12 to 15 degrees hotter than the rest of the cylinders. In order for me to keep #6 under 400 degrees I have to keep the cowl flaps about 1/2 way open.

Have you seen this #6 cyl temp rise over a certain period of time in relation to the others? Is the trend continuing?

The reason I ask is that there are myriad reasons why this could be occurring. From the simple: when the cowling was last taken off and upon reinstall part of the flexible baffling was inadvertently not sealing well - to the complex: a piston ring has broken and there is additional friction causing heat and eventual failure  - to everything in between.

I’m also curious... at what power settings / altitude are you seeing the temp go past 400dF where you have to open the cowls?

[DVA]

On 8/1/2016 at 0:30 PM, Casey said:

 IVestas always been told if you run a cylinder over 400 you're doing damage to it.

I disagree with the totality of this statement. A better way to say it would be “As often as practicable and when able, keep CHT’s below 400dF to promote maximum cylinder life and respect the maximum CHT of the POH”

400dF is not a hard and magic number; it is a reference based loosely on some metallurgy changes that begin to occur at a more rapid rate after about 400dF. There are tons of references you can find on this and by all measures it is a rather conservative number - but not a bad number to shoot for! 

That said, I (and many others) do not routinely run CHT above 400dF for all the good reasons. But to say that you are definitely doing damage to the cylinder at 400dF and implying you are not doing damage to it at 399dF is as ridicules as the theory that there is no Santa Claus.

Lycoming will and has vehemently defended that their engines can be run up to redline CHT (in the M20M that 500dF) when required without damaging the engine ... while at the same time they will say that its better to keep them under 400 in cruse for longevity. It’s all about care and balance in my view.

If I were on a climb-out and I wanted to get the most performance I would not hesitate to moderately exceed 400dF for the entire climb out period of time. Sometimes in hot summer cruise when I want to go fast I will see my #3 (my hottest) run at 410dF while the others are under 400dF cowls closed and I don’t blink an eye. I would start to take corrective action if they were heading much higher but I would not declare a CHT emergency and land for a borescope look if it happened. 10-15df one way or the other is just not enough swing to make a difference, and the accuracy of the measuring system is nowhere near exact either.

That said, my habit however is to treat this engine (any engine for that matter) with TLC. I mostly run LOP, accept the slight reduction in speed and see CHT’s well below 400df 90% of the time.

Let the flames begin :-)

 

[carqwik]

What the Mooney M20M POH says for engine operations and what's best for the engine aren't always aligned properly....just because you can doesn't mean you should do so.

I agree, no magic to 400 degrees...just more of a guideline than anything else.

[CharlesHuddleston]

Old thread, revisited. I just got my K back from a full overhaul. Everything is running great, including the temps.... until I fully close the cowl flaps. When fully closed, the #6 CHT will begin a stead climb to over 425 while the rest of them remain in the 360-380 range. I understand there are a lot of variables involved (RPM, fuel flow, mix, MP), but I’ve experimented with all of the above. The one consistent is the the #6 will begin an immediate climb. I would have thought with it being in front, that it would stay coolest. My first thought after reading and researching goes back to the baffles. They were not replaced. While they don’t look to be in bad shape, they are a little wavy. Also wondered if there could be an outflow issue with the flaps closed? But it seems if this were the case, the rest of the cylinders on that side would climb as well. Appreciate any and all thoughts and input. Going to call Gee-Bee on Monday and price a new set of seals. Also, have about 15-20 hrs since the overhaul. ‘82 K model, LB engine, intercooler and Merlin wastegate. JPI 800. Fixing to download the JPI data and review that as well. 

[larryb]

From what I read here and on beechtalk it is hard to make sense of airflow. I would just say don’t do that. I never fully close mine, prefer about 1/4 open in cruise for best temps.

 

[JohnB]

That’s fascinating you post this now, my M is in maintenance now checking out the exact same issue, #6 running hotter than the others. Also discovered that my cowl flap motor needs repair or replacing , which is a separate but related issue. My guess is that it’s the baffling on mine, but I’ll keep you posted, also curious what others are finding. 

[alextstone]

My Bravo is in for annual.  The #3 cylinder failed the compression check - exhaust valve leak was suspected.  That cylinder was running 20 degrees hotter CHT's (not sure if this is related).  The borescope of the valve looks like this:

I have a spare cylinder...just for this occurrence.  My question (to stay on topic with this thread) is:  

Could the increased CHT be a symptom of this valve issue?

[carusoam]

Hey Alex,

That type of valve issue usually comes with two quirks in the data...

1) Higher EGT on that cylinder as more burning fuel is escaping past the valve...

2) Lower CHT on that cylinder as some of the heat usually generated inside the cylinder is now getting out before it can be absorbed by the cylinder...

3) wondering if the Bravo would start showing higher oilT as the wet head may be working a bit of overtime...?

Looks like you have caught it early on compared to other valves pictured on MS...

Great catch!   Thanks for posting pics.

Got any engine data to share using Savvy?

Best regards,

-a-

[alextstone]

22 minutes ago, carusoam said:

Hey Alex,

That type of valve issue usually comes with two quirks in the data...

1) Higher EGT on that cylinder as more burning fuel is escaping past the valve...

2) Lower CHT on that cylinder as some of the heat usually generated inside the cylinder is now getting out before it can be absorbed by the cylinder...

3) wondering if the Bravo would start showing higher oilT as the wet head may be working a bit of overtime...?

Looks like you have caught it early on compared to other valves pictured on MS...

Great catch!   Thanks for posting pics.

Got any engine data to share using Savvy?

Best regards,

-a-

I did not see the two quirks you mentioned and as a matter of fact, I recently worked with GAMI to tune my injectors....

I wonder if tuning injectors can mask problems to some degree...

Interestingly, I was seeing oil temps just a bit higher than last summer (205 - 208 degrees F vs 200 degrees last year)

My AI wants to pull the cylinder and have a better look at the valve.  He seems to thing that profiling might not be out of the question rather than a cylinder swap....what are your thoughts on this?

Alex

 

[carusoam]

It could be a simple valve, and seat job... or plumbing check for the wet head...

Being only a PP, I would defer the question to somebody like @M20Doc who has the real experience...

 

The usual cause of the hot spot on the valve is its rotation has gotten stuck....

something to consider... The Gami spread will be changing with the changes of the valve sealing...

it is possible the Gami injector selection process would accidentally take this into consideration.... getting a new valve / seat would reset everything back to essentially new conditions...  and changing the Gami spread that was used...

If the valve got sticky before the gamis got added... there may be room for improvement...

It may be a challenge to know when the stickiness began...  but there are well known fingerprints in the engine monitor data that can be found just by looking... starts by reviewing EGT for that cylinder and looking for a sawtooth pattern... got a JPI 900?

A good review of engine data may be in order as other cylinders may be showing a similar pattern...

see if Paul is around... @kortopates

Checking Gami spread before and after the cylinder work will give some data to review, in the event more questions arise... having a JPI 900 is great because it tracks a ton of other data points with the CHT and EGT... 

Best regards,

-a-

[kortopates]

The valve looks pretty badly burnt. We have had some success lapping a valve in situ early in the burning stage with a hot spot rather than actual burnt spot. We've  actually saved some that way. That valve looks too far gone, but you would also want to look at it raised up (open) as well as the seat with the valve raised for damage and guide for excessive wobble. If it still looks good, it wouldn't hurt to try lapping it, and if successful you'll get compression back with a valve that should resume normal rotation. But to my eyes that valve looks too far gone and I expect you'll want to replace the valve, grind the seat and check the valve guide. An engine shop can turn that around in a day or at least inspect the cyl to tell you if you want to repair the existing one or replace it with another or OH. 

Gami spread isn't affected by exhaust valve leakage, only induction system leakage and a leak of any significant size can't be masked by a leaner injector in a turbo or richer injector in a NA aircraft. Plus it should be pretty obvious at idle. This why our Savvy Test profile calls for performing gami sweeps at WOT in NA aircraft and for turbo's using a MAP = ambient atmospheric pressure; that will pretty much eliminate symptoms for induction leaks.

[JohnB]

Mechanic done, with mine he cleaned my #6 fuel injectors and problem solved, #6 is now just like all of the others. My baffles were ok this time. 

[carusoam]

Great follow-up John!

Best regards,

-a-