High CHT on one cylinder?

[DaV8or]

My number 3 cylinder runs the hottest on my Mooney. This makes sense to me because it is in the back and does not have the benefit of airflow through the oil cooler. However, on my last flight, it set off my engine monitoring alarm for the first time because it briefly rose to over 100 degrees hotter than the coldest cylinder and that is the threshold for the alarm. All is still well because my cylinders run really cold and at the time this happened, number three had only reached 360.

 

I couldn't think of any situations that would cause just one CHT to raise and yet the EGTs are all normal and relatively even except a cooling issue. I keep my plane in a hangar, so a bird's nest isn't likely, but you never know. When I got home I pulled the cowling to do an inspection. Before I pulled the top cowl off, I checked with a flashlight to see that the rubber seal was proper against the cowl and it was. I found no obstructions, no parts missing and no defects. Looked as good as ever.

 

Can anybody think of a reason that one cylinder CHT goes up without a change in EGT other than cooling?

 

I don't know about you other vintage guys, but I have found my cowl flaps to be pretty much worthless. Open, closed, not much difference. I have my flaps adjusted to be as flush as I can get them when closed. I guess I could adjust my right one to be a bit more open, but given they don't do much anyhow, I'd rather not add the drag. I suppose modding the baffles is verboten, so any ideas on how to cool a cylinder down?

[mooniac15u]

I'm curious about your other CHT readings.  When your #3 CHT hit 360 deg your other CHTs were around 260 deg?  In a J the bottom of the green arc for CHT is 300 deg.  What phase of flight were you in when #3 hit 360?

[kmyfm20s]

360 not bad but 260 seem very low. How rich or lean where you running at the time? Even though you had even EGT's what where they?

[sellis]

Check the fuel injection nozzle at that cylinder. Possible it could be partially clogged. Clean the nozzle.

[MooneyMitch]

Dave, you might also switch probes with cylinder #1 in order to verify integrity of the probe/wiring, etc. 

[Bob - S50]

One other possibility is a small exhaust leak from the #1 or #3 cylinder with the exhaust blowing onto the CHT probe, giving a false reading.

 

Bob

[mooniac15u]

Check the fuel injection nozzle at that cylinder. Possible it could be partially clogged. Clean the nozzle.

 

A clogged injector nozzle usually results in a higher than normal EGT because the cylinder is running leaner than normal.  CHT isn't impacted as much.

[DaV8or]

I'm curious about your other CHT readings.  When your #3 CHT hit 360 deg your other CHTs were around 260 deg?  In a J the bottom of the green arc for CHT is 300 deg.  What phase of flight were you in when #3 hit 360?

 

I was in cruise and trying to go LOP once again. I utilize the big pull method. Somewhere in there it alerted me to the CHT issue. It ran like crap as usual and the alert sealed the deal, so returned to ROP. My front cylinders never go above 300 except in the heat of summer and on climb out.

[DaV8or]

One other possibility is a small exhaust leak from the #1 or #3 cylinder with the exhaust blowing onto the CHT probe, giving a false reading.

 

Bob

 

I saw no evidence of this, but I wasn't looking for it either. I'll check out. Seems kind of a remote possibility, but I'll check that. Ever heard of this happening before?

[DaV8or]

360 not bad but 260 seem very low. How rich or lean where you running at the time? Even though you had even EGT's what where they?

 

Not rich at all. I was pretty dang lean. I try to run LOP (but is less and less workable), but when I go ROP I go peak at 65% usually. I am occasionally known to go fight a headwind, or get home quickly with 75% ROP + 125 degrees, but not this day.

[DaV8or]

Dave, you might also switch probes with cylinder #1 in order to verify integrity of the probe/wiring, etc. 

 

Might try that if it persists. I hate messing with those connections and it seems to be working OK, but who knows for sure, right? It's not super out of line because number 4 is only about 20 degrees colder, which I think makes sense because it has the oil cooler and more air flows through. In fact my left cylinders run colder than the right. In a perfect world, I wish I could be allowed to experiment. I would love to fabricate a variable opening in the back baffle over number 3, kind of like a Super Trap muffler on a motorcycle, to dial in the temps to match the left side without messing with the cowl flaps.

[kmyfm20s]

So this only happened during the leaning process going to LOP? After you went back to ROP and you where in cruise what was the CHT spread?

It sounds to be that you have a large GAMI spread with a baffling/shield problem. These engines should run LOP well. I would bet that your #3 cylinder is the richest and has the worst air flow for cooling around it. #1,2,&4 being more closely matched in both FF (leaner than #3) and having better air cooling. I suspect you are seeing cylinder #3 is cool enough on the ROP side because it's being cooled by fuel but is still running hot compared to the others because of the baffling/shield. When you go LOP it's the closet to peak so your CHT the hottest and the others are well LOP so are cool but giving the large CHT spread.

Ross has posted on wedging some silicone baffling in between the cylinder and the shield to increase airflow on the #3 cylinder. At that point it comes down to air, gas and spark. I would next go after the air first and check for any induction leaks by tighten up all the intake flanges and check where the intake tubes go into the plenium(sp?), I had to put silicone around mine. Tighten the exhaust flanges while you are there. See if this tighten up your GAMI spread and smooth out your LOP operation. Go for a flight check your GAMI spread and do an in air mag check that will let you know where to go next.

[Bob - S50]

I saw no evidence of this, but I wasn't looking for it either. I'll check out. Seems kind of a remote possibility, but I'll check that. Ever heard of this happening before?

I have not seen it personally, but here is something from the troubleshooting/diagnosic section of our engine monitor manual:

 

CHT more than 500°, EGT normal. Adjacent EGT may be low...

Leaking exhaust gasket blowing on CHT probe....

Look for white powder around cylinder to determine leak area....

[PTK]

My number 3 cylinder runs the hottest on my Mooney...

 

...I couldn't think of any situations that would cause just one CHT to raise and yet the EGTs are all normal and relatively even except a cooling issue. 

 

...Can anybody think of a reason that one cylinder CHT goes up without a change in EGT other than cooling?...

 

 

Dave, here is an article that sheds light into these issues and may be of help to you.

 

http://www.avweb.com/news/maint/egt_and_cht_interpretation_198791-1.html

[DaV8or]

Go for a flight check your GAMI spread and do an in air mag check that will let you know where to go next.

 

I would love to do a GAMI test, but if you watch the video, you'll see why I can't. I might try the mag check, but my understanding is that a faulty mag will cause a raise in EGT and I don't have that. However, My mags are very near 500 hours and I intend to rebuild them at annual this year. The spark plugs are new with about 12 hours on them. All my intake gaskets have been replaced about 12 hours ago.

 

Anyhow, your theory of unequalized cylinders combined with a baffling issue is the most likely cause of my high CHT spread. Finances are such that I really don't have spare money this year to chase LOP gremlins down a rabbit hole. These kinds of nebulous problems tend to cost a lot of time and money. The plane runs smooth just fine ROP. Likely, LOP ops is a "mod" I will throw money at and add to the plane in the future when I am more certain of income than now.

 

<edit> I wanted to embed a You Tube video here that I made illustrating my erratic fuel flow, but how to do that seems to be above my pay grade.   Lets just say this, the GAMI lean test is not possible.

[DaV8or]

Dave, here is an article that sheds light into these issues and may be of help to you.

 

http://www.avweb.com/news/maint/egt_and_cht_interpretation_198791-1.html

 

That article pretty much sums up what I had already deduced. Cooling issue. I will check for the "blow torch" effect, but I kind of doubt that one. The other possibility they offered up was "unusually high friction in that cylinder". I have no idea how you do a definitive test for that, but I will say that when I pull the prop through by hand, it seems quite normal and I hear no scraping, or grinding sounds. I also did pull the top spark plug out and looked in with a flashlight. I don't have a bore scope. What I did see looked perfectly healthy.

[Marauder]

I would love to do a GAMI test, but if you watch the video, you'll see why I can't. I might try the mag check, but my understanding is that a faulty mag will cause a raise in EGT and I don't have that. However, My mags are very near 500 hours and I intend to rebuild them at annual this year. The spark plugs are new with about 12 hours on them. All my intake gaskets have been replaced about 12 hours ago.

 

Anyhow, your theory of unequalized cylinders combined with a baffling issue is the most likely cause of my high CHT spread. Finances are such that I really don't have spare money this year to chase LOP gremlins down a rabbit hole. These kinds of nebulous problems tend to cost a lot of time and money. The plane runs smooth just fine ROP. Likely, LOP ops is a "mod" I will throw money at and add to the plane in the future when I am more certain of income than now.

 

<edit> I wanted to embed a You Tube video here that I made illustrating my erratic fuel flow, but how to do that seems to be above my pay grade.   Lets just say this, the GAMI lean test is not possible.

 

 

If you have already uploaded the video to YouTube, there will be a "share" button that will allow you to copy the link. Just copy it and paste it in your thread here. What is the name of the video, I can do it for you.

[Marauder]

I'm curious to see it. I have been a ROPer and have not even tried to see if I can run LOP. Mostly because I want to "get there sooner" than "get there cheaper".

[carusoam]

Thus defining the "Mooney Conundrum"....

Best regards,

-a-

[PTK]

I'm curious to see it. I have been a ROPer and have not even tried to see if I can run LOP. Mostly because I want to "get there sooner" than "get there cheaper".

If you can run LOP you'll "get there sooner" by "getting there cheaper for longer!"  

[kmyfm20s]

Everything I mention you can do yourself as I understand. Exhaust bolts are 1/2", intake flanges are 7/16" and check the tubes. If those are effected that will tighten up your GAMI spread from induction leaks and any excessive CHT from exhaust leaks blow torching the probes.  The silicone peace between the cylinder and baffle shield is easily wedged into place and will help with airflow to cool the #3. 

[DaV8or]

If you have already uploaded the video to YouTube, there will be a "share" button that will allow you to copy the link. Just copy it and paste it in your thread here. What is the name of the video, I can do it for you.

 

OK. I thought it had something to do with the "embed" link that is on You Tube and here. Anyhow, here it goes-

 

[DaV8or]

I'm curious to see it. I have been a ROPer and have not even tried to see if I can run LOP. Mostly because I want to "get there sooner" than "get there cheaper".

 

Sorry to disappoint. My video has little to do with leaning techniques, or the result. It's just a demonstration of my crappy fuel flow indication.

[orionflt]

the jumpiness could be because of the FF transmitter installation. the transmitter has to be vertical with the fuel flowing up (hard to do in a mooney) or horizontal position lower then the fuel servo inlet. also the fuel line should be secured to limit vibration. I have the MVP-50 also and my FF is pretty steady but i do get the occasional jump.

 

brian 

[carusoam]

Dave,

Along with what Brian has stated above...

Is there an averaging feature with the AVP that would smooth out the jumpiness?

Has it always acted like this? If this is a new behavior, a cleaning of the transducer may be desired. Look fo leaks, such as air entering the system...

Fluid flow measurement prefers long straight entry and exit tubing of identical IDs as the transducer.

Any angles to the tube should be large radius curves. Avoid 90deg angles and differing tube sizes.

You do you have a fuel pressure gauge there as well. If the FP is fluctuating...

My FF is constant to .1gph. I don't have FP, but if it varied 1 psi, that would be worth identifying what's causing the variation...

Not trying to generate fear. But you have two independent instruments that are usually more stable than what are shown in that video.

Best regards,

-a-

Hope this helps....