Low CHT in one cyllinder

[AdventureD]

Hi all,

Bought a Mooney Bravo in December and have about 75 hours on it.  Trained with Will Wobbe and Don Kaye after 15 years of not flying.  Highly recommend both.  Will helped me ferry the plane and get back into flying--tons of reeducation--and Don taught me more about landing airplanes and careful attention to detail than I learned through all my private and instrument training, by far.  But I still sometimes come in too fast and bounce em now and then (sorry guys).  :).  Love the airplane.

A couple months ago the CHT probe on #6 went bad.  After learning it was the probe and not the cylinder (only 350 hours since factory reman) I didn't worry much.  Compression in #6 was high 70s and #6 EGT was good, so all seemed fine.  Then I had the CHT probe replaced.  Now it shows about 100 degrees cool, still with a EGT in the right range (see photo).  #6 was not cool before the probe went bad.  Instrument is an Insight G2.  Engine seems smooth enough, EGTs seem fine, and power and smoothness seem fine.  Replaced the spark plugs a couple months ago--new champions.  Mag drop seems a little steep unless I do the run up with ground leaning, in which case it seems normal.  Nothing weird in flying.  Very slight roughness?  Maybe, but I'm probably paranoid.  I'm on a trip now (2500 miles from home!).  Mechanic says low CHT is not a critical indicator of poor cyllinder health; EGT is a better indicator of health; should check when I return.  

Agree?  Any thoughts?

[carusoam]

A quick test for a probe that may need some attention... is to swap it with the cylinder next to it...

You might find that something can use some cleaning, it may be just a measurement challenge, not an actual engine challenge....
 

All the CHTs should be as close together as possible... 

Having 100°F of instrument error, won’t make you feel any better...

If the CHT was actually 100°F lower... you would want the other five to do the same....   
 

Do you see any similar offset when the engine is cold, before starting?

 

What would really help to see... have you sent your engine monitor data to Savvy, clicked the share button, and post the link here?

We could talk a lot of maybe.... Or we could just look at your data in graphic form... for free... 

Best regards,

-a-

[AdventureD]

More Insight G2 travails ---

Is this instrument helping me, or is it just being a pain in the neck?  Here's what has happened since I purchased the plane in December 2019.

1. Instrument had the blue screen of death (well, actually, just snow) a few months ago.

2. Fixed the instrument by sending back to Insight (not cheap, and seems all they did was reset something).  A couple flight hours later, the #6 CHT probe failed.  I worried that it was a cyllinder, but the mechanic said it was the probe.

3. Fixed the #6 CHT probe at annual, but #6 now reads 100 degrees lower than the other CHTs even though it was a bit hotter prior to the failure described in (1).  All analog gauges are reading normally, engine is smooth, and mag check is normal if the plane is sufficiently leaned on the ground.

4. Mechanic says not to worry about the "cold" cyllinder, as EGTs all seem about normal, and EGT is a better indicator of engine health.  #6 EGT is about like the rest.   And as noted in (3), all analog gauges seem to be where they're supposed to be.  The Insight is an add-on instrument, and had it not been added to the aircraft, the pilot wouldn't have seen a thing that is out of order.  As it is, the pilot is wondering by now, "what is going on?"

5. On flight from east coast to midwest (prior to planned trip to home base on west coast in a few days), the Insight TIT suddenly massively redlines, while the analog gauge remains right where it should be based on experience given fuel flow and MP and RPM settings.  So now, the situation is: (i) the #6 CHT remains likely wrong, AND (ii) the Insight TIT is going nuts.  All while all the analog gauges are in the normal range, EGT for each cyllinder on the Insight gauge (and analog gauge for the specific cyllinder monitored), remain normal. 

7. Based on some debugging on the ground, I find that each mag check in a run-up generates EGT and analog TIT increases (the Insight TIT is redlined) as I understand is expected. 

So...Is something wrong?  Probably the Insight probes are kaput or something else is wrong with the Insight?  I understand the Insight TIT probe and analog TIT probe are in a slightly different places.  Could the high TIT reading from the Insight be some exhaust problem or some other problem, or is it likely that the TIT probe for the Insight is bad?

My thought:  The likely answer is that the Insight G2 is repeatedly being a pain in the neck.  But maybe you can convince me that I'm getting information out of it that is actually useful and that I should heed some warning.

Happy flying,

Dan

[carusoam]

Dan,

How much do you like touching wires?
 

1) The engine monitor is one of the more simple things you can get straightened out...

2) It is one of the more challenging things to hand to somebody else to figure out...

3) TIT sensors live in the harshest environment 

4) EGTs are in 1/6^th as harsh..

5) CHTs aren’t in a very harsh place at all by comparison...

6) The odd man out syndrome is often related to where your ship’s gauge is reporting from...

7) If your mechanic can’t explain this logically to you... you may want to find one who can...

8) Could be him, Could be you... the combination needs some help....

9) Broken sensors are easy to determine...

10) swapping them with the one next door usually tells a lot...

11) How do they all read when everything is cold?

12) got any odd sensors hiding under spark plugs, imitating gaskets?

13) got any called a piggy back, not sitting in a well...

14) If any of the TCs is Not reporting correctly, there is a calibration mode for the instrument....

15) there aren’t that many insight engine monitors in the wild around here.... of the few that are around... they get used without issues... really nice for doing calculations for Gami spread... when connected to the FF monitor...

16) use the search function for insight see what comes up...

17) See what DonKaye uses... he is always a leader in aviation and electronics....

PP thoughts only, not a mechanic...

All stuff I read around here...

Lets get it working right!

Best regards,

-a-

[MikeOH]

CHT smells like a probe problem.  As has been suggested, super easy to swap with adjacent cylinder; if it follows the swap you have your answer; bad, or incorrect probe type (J and K are common but NOT interchangeable).

TIT gauge seems more like a wiring problem (sudden onset). Take a look and see if the probe wires are broken or kinked; start at the probe and work backwards as far as you easily can. I'm not sure how the gauge behaves open-circuit. I'd call Insight and ask. When I called with an issue on my G3 I swear I must have been quickly connected to the guy that designed the thing. Knew immediately that it was a software issue and fixed me right up by walking me through the free download/install process.

[FloridaMan]

Check probe location as well. Might just be the jug that has the required factory CHT probe on it and is in a different location than the other probes, or it could be a connection issue somewhere. 

[GeeBee]

If after a probe swap, the #6 is still cool, check the probe well. Sometimes stuff gets in there and acts as an insulator.

A word on the G2. It does not like cold. I had an airplane in which it would offer the "screen of death" until I warmed up the cabin. Then a power down and power up would fix it.

 

 

 

[AdventureD]

Thanks all.  Switched #6 and #4 probes and the the difference persists—probe.  But it’s a brand new probe.  Maybe wrong type—it looks slightly different than the others.

TIT—Took it out and see the probe is cracked.  Probe.

inspected exhaust.  No cracks, no leaks.

Everyone on the ground said it sounds great.

Flying from WI to CA tomorrow knowing the issues are with probes.

[David Lloyd]

Once, I replaced an EGT probe with a new probe and it read about 200 degrees lower than the others. It was within a degree of the others when cold.   After putting up with it for a couple years, replaced it with another new probe.  That read normal and in line with the others.  

[carusoam]

Most of our thermocouples are K type...

K-type TCs may be color coded to standards...

Yellow and red...   https://www.automationdirect.com/adc/shopping/catalog/cables/bulk_multi-conductor_cable/thermocouple_-a-_rtd_extension_wire_-a-_cable/thermocouple_wire_(type_k)/thmwk-50-02?gclid=Cj0KCQjw7Nj5BRCZARIsABwxDKKGkkRQjPU_fN4Zh6FzSHO6pbICuZ2x_418NsjEFTRCWqTlPZlhOLMaApvlEALw_wcB

When a plane is new to you... you may find TCs that have been absurdly extended in all types of goofy ways... Including The use of copper wire...

PP thoughts only, not a mechanic...

Best regards,

-a-