EGT/CHT Troubles

[thibault]

Has anyone else had trouble with erratic EGT/CHT indications using the Dynon supplied sensors?

Been flying for years and putting up with erratic indications. Have gone over all the crimps with a quality ratcheting crimper with some improvement, but it doesn't last. Have replaced the EGT sensors after many years, when they wore out, and the problem returned with the new ones as well.

Finally decided to cut off the fast-on style connectors and just butt splice the ends together. This meant that I stripped the sensor end for the first time (these come with the connector already on that end). When stripping that end of EGT or CHT, I noticed that there is a woven insulator under the plastic. It is a pain in the butt to get rid of that stuff, but I did and crimped on the butt connector. The brownish wire that goes to the EMS box has only the plastic insulation, so it strips easily.

I wonder if the factory supplied sensors have less than ideal assembly techniques and that this compromises the signal integrity.

In any case, after one test flight the readings are again very steady. For now, at least.........

 

[Carl_Froehlich]

At 250 hours on an RV-10 I had two EGT probes fail. The replace probes are working. I now have another EGT probe starting the same failure sequence of the reading rapidly jumping around. On the first two probes this happened shortly before they completely failed.
I also tried the "crimp the connector" fix with little luck. When the probes failed I checked them again after I cut off the connectors. They were dead.
I got a note from Dynon awhile back that they were working the issue. Not sure if the current probes are from a different vendor or not.

Carl

 

[Dynon]

We do make running improvements to parts/vendors/etc, and our EGTs have been improved over time. Both the connections and the probe materials themselves have received running improvements over the past few years.

 

[vlittle]

I did the butt splice trick and it solved all of my erratic egt and cht problems. In general, connectors of any kind fwf are failures waiting to happen, but these probes measure millivolts and so it shows up early. Fortunately I put service loops in the wiring so the change was easy.

Better quality terminals help but this hot, shaking environment is tough on connections in general.

Vern

 

[jakej]

I did the butt splice trick and it solved all of my erratic egt and cht problems.  In general, connectors of any kind fwf are failures waiting to happen, but these probes measure millivolts and so it shows up early.  Fortunately I put service loops in the wiring so the change was easy.

Better quality terminals help but this hot, shaking environment is tough on connections in general.

Vern

Aha - maybe I have a believer here ;D ;D

Jake J

 

[NASA515]

I have two probes - both failed by 200 hrs. One was fixed by working on the connectors. The other is kaput despite my best efforts. Have a new probe and will install when time permits.

Bob Bogash
Rv-12
N737G

 

[GlennB]

We too have had the original EGT probes fail.  In our case (twice) it was an internal failure of the wire, caused by being required to bend 90 degrees after leaving the probe.  Additionally, because the wire core is very fine, it seems difficult for a crimp terminal to get a good grip on it.  I had previously reworked the crimps to fix occasional erratic indications.

Both problems were solved by replacing all the probes, and they've been working fine ever since.  While I hesitate to recommend any product in preference to the usual high standards of Dynon, these were the solution for us:

http://thesensorconnection.com/egt-probe-thermocouples/sensors/exhaust-gas-temperature/egt_muffler_clamp_probe.shtml

 

[mmarien]

I replaced my EGT probes shortly after I installed electronic fuel injection. I was running too close to peak EGT (+/- 1600F) and eventually fried them all. I replaced them with better quality (read more expensive) probes and since put over 300 hours on them without any failures. or crimping problems.

The probes I used came with sleeve type connectors with a set screw but I used the normal blade type connectors to match the original connectors. I used a ratchet type crimper. The connectors themselves sometimes fit loosely together. They can be adjusted by squeezing them with pliers.

In that type of harsh environment, I think you have to consider the probes as consumables that need to be replaced once in a while. 

 

[vlittle]

I reworket all of the egt probe conections by repacing with barrel crimp connectors. That fixed everything for a while but now I have a probe failure. It has odd behaviour, working fine while the engine is running but not when shut down.

Nevertheless, it's time for a replacement after less than 70 flight hours.

For refererence, I never had an EGT failure in 500 hrs in my 9A which I sold last year. What's the best choice from ACS?

Thanks, Vern

 

[DHeal]

Looks like I may need to replace the problematic fast-on connectors on my RV-12's EGT wiring. They can't seem to consistently stay electronically connected. My question: Is it OK to cut off an inch or so of the EGT's wiring leads to make a new connection? I have heard of some EGT wiring set-ups that are sensitive to trimming the length of their leads.

 

[swatson999]

Remember that for EGTs, the absolute value is really pretty irrelevant...it's the peak and the delta from the peak that matters.

I replaced one of my EGT probes a while back, and it must have been a newer version, because it has always read higher than the other 3. But...it doesn't matter, as long as I can find peak EGT on all the cylinders during leaning.

 

[waveflyer]

This is obviously a common issue which probably needs to be addressed by DYNON. I fly an RV7 and despite re crimping I get constant EGT reading problems.
Four red X's before start up and then what appear to be good readings during flight.
However, more recently one or two drop out and back in during flight.
DYNON, what has gone wrong please?

 

[rlallen1]

At 70 hours my dynon EGT sensor became erratic... Dynon said something to effect of "they are priced low and not meant to last". unhappy with that comment... I bought new probes from KSAvionics...much higher quality and made to last. Highly recommend them..
300 hours later, no problems

http://www.ksavionics.com/products/catalog_ksa_probes.php

 

[Dynon]

To answer all of the last few questions together: Yes, it's OK to change the connectors / cut / splice / etc. Just make sure not to add a temperature change across your new junction (ie, no connectors at/across the firewall). EGTs exist in harsh environments, with lots of heat and vibration. So one way they fail is the failure of the the actual probe that's in the exhaust. This can be hard to predict: some engines have consume probes regularly; others practically never. We have, over time, made running improvements to our EGTs that have helped with their longevity. Another issue can happen at the crimp junction. There was a time where the spade connectors on our EGTs didn't perfectly match the connectors on the harnesses, but we've also improved that over time as well.

 

[dynonsupport]

This has been a recurring discussion that flares up periodically. You can search the archives for previous threads.

We've seen two recurring issues with EGTs in Technical Support:
1. The connection between the harness (the stiff brown wire) and the probe wires are problematic. Having a reliable, solid electrical connection is critical for thermocouples and a poor connection is the largest (vastly largest) source of issues with CHTs and EGTs. If the "faston" connectors furnished by Dynon Avionics (or completely re-terminating with replacement connectors) are problematic for a particular installation, your assistant forum tender thinks that these connectors should work well - strip the wires completely bare, overlap them inside the "barrel", and twist on the Allen screw.

We've also seen some customers decide to use industrial thermocouple connectors. If you do so, make sure you buy the appropriate connector - Type K for EGTs, Type J for (thermocouple) CHTs.

2. Some engines... some installations... run hotter than most and the exhaust actually burns through (abrades) the part of the probe projecting into the exhaust stream. All we've been able to suggest in those installations is to try another brand of EGT probe.

This is obviously a common issue which probably needs to be addressed by DYNON. I fly an RV7 and despite re crimping I get constant EGT reading problems.
Four red X's before start up and then what appear to be good readings during flight.
However, more recently one or two drop out and back in during flight.
DYNON, what has gone wrong please?

 

[n456ts]

Ugh... Spade terminals? Unsealed terminals?

Use the good stuff (It's an airplane!). Deutsch connectors (now TE?), or Amphenol generic. Such as:
https://www.digikey.com/product-detail/en/ATM2PS-CKIT/889-1242-ND/4415026
Or even the trusty MetriPak 150-sealed, or a weatherpak (use the correct seals! ie, not green!).

Even upgrade to gold terminals...

 

[uniflying]

I had fluctuating temps until I removed all the consumer grade crimps and replaced them with proper aviation standard Environmental Crimps: M81824/1-1 M81824/1-2 M81824/1-3 - use the proper crimp tool AD-1377. Expensive but they work, and you kinda want that on a plane.

I wouldn't use any connectors or cheap crimps on CHT or EGT lines. It only takes about an extra 5-10 minutes to crimp them properly.

 

[jakej]

Exactly as uniflying says, that's the way it has worked for me & I've done many, many installs without any serious issues.  In recent times I've sprayed the connections with LPS2 or 3 & Inox or Lanox - as we're talking millivolts here I find the 'sprays' reduce the possibility of oxidization affecting the connections.

 

[mrdaud]

From a GE thermocouple training manual comment:

"Thus twisting, welding, soldering, crimping - they all work, until... until corrosion sets in between the connections. Thus, twisting is the least preferable over time because the metal is neither fused nor crushed together sufficiently to form what's termed "a gas tight connection."

I used to weld wires with a special TC wire welder, which is the preferred way, but, 1) welders are several thousand dollars, and 2) they are permanent connections.

I hate to beat a dead horse, as I’ve posted this several times before, but if you use the thermocouple specific connectors listed below, you will fix your connector problems.  They use the same metal as the TC wire.  I've used these for years in industrial processes, and after many early problems with my Dynon supplied TC's and frequent emails back and forth with Dynon, I took my own advice and switched to these connectors. Since switching, I've had trouble free operation for over three years now. Not as cheap as twisting, but for only about $30, they are worth your risk. And they are reusable if you have to change thermocouples.

As noted above, I've posted this before, but it is worth doing again.  There is a better way.  Get rid of any spade/barrel connectors!!!!  Use dedicates connectors made with the same metal as the wire, and they are easy to install.  Fixed all my problems.  You can purchase the connectors from Omega at www.omega.com.  There are male and female genders and J & K type connectors, and are reusable.  They are about 1/2" wide.  Well worth the small additional cost. If you are having TC connections problems, this is a guaranteed fix.
SMPW-CC-K-M  $3.50 ea
SMPW-CC-K-F   $3.25 ea
SMPW-CC-J-M   $3.50 ea
SMPW-CC-J-F    $3.25 ea