EGT Anomaly

[skippydiesel]

Hi,
I have a Rotax 912 ULS. / Dyon Skyview Class SV-ADAHRS-200, SV-EMS-220, with 2 Dynon EGT K Type Thermocouples/Probes PN. 100405-001
Today, on start up my EGTs were working fine.
Taxied out to runup bay and Number 1 EGT readout went blank & I received an EGT warning.
As I prepared to return to hanger, the EGT came good.
Went for a fly. Engine running just fine.
About 30min into the flight , EGT No 1 went blank again. Also had very brief/flash readings above Max EGT.
Retuned to airfield.
In situ, visual/external of EGT's leads/connections all look normal/good. Connections nice & firm.
Check resistance /continuity with multimeter. Both EGT's have continuity. No 1 resistance significantly higher than No 2. Unable to do a full check as engine still hot.
Will return tomorrow to do a ADAHRS diagnostic download & test Probes with heat gun

Do I have a EGT, Probe or ADAHRS problem?😈

[KRviator]

Pretty sure I had to replace one of my Dynon EGT probes early in the piece, was reading off-scale-high at times. Easiest way to test to do is swap #1 + #3 probes to see if the problem follows the probe to #3. If yes, replace the probe. If the problem stays and stays at #1, run, do not walk, to your nearest pharmacy and purchase a tube of KY because it'll lessen the pain that's about to come.

[Reynard]

If you have 4 EGTs, you probably have 3 too many.

[skippydiesel]

Only two EGTs on #3 & #4.

 

Swapping EGT's on my installation, is technically  a "no brainer" but unfortunately very time consuming - I had hoped that someone else may have had similar symptoms of a failing thermocouple.

 

Does anyone find it interesting that the two EGT's have every diffident resistance readings?

😈

[sfGnome]

You would expect the resistances to be the same merely because they are built the same. Having said that, a thermocouple is a temperature controlled voltage generator (ie at the point of the couple), not a temperature controlled variable resistor, so the actual resistance shouldn’t matter greatly (the input impedance of the measuring device will be comparatively very high). Regardless of that, ‘divide and conquer’  is your diagnostic friend. As kr said, swap them. There’s no cheaper (or more accurate) way to diagnose the fault. 

[BurnieM]

Not sure about the ULS probes but I believe the 912IS probes are $300 each.

 

[skippydiesel]

On 08/08/2026 at 10:17 PM, BurnieM said:

Not sure about the ULS probes but I believe the 912IS probes are $300 each.

 

Dynon PN. 100405-001 for Rotax ULS, $66 from https://horshamaviation.com.au/product/egt-probe-hose-clamp-1-00-2-25-lyc-cont-sup/😈

[Mewp]

Had a similar problem and found the connectors between the Probe and the Dynon wiring loom ( simple spade connectors)  had become a loose fit. Re seated them and problem solved. Will replace with correct thermocouple joiners at some stage.

 

Edited August 10 by Mewp

[Reynard]

Nah, all good.

 

[skippydiesel]

Hi Reynard,

 

Wow! One, EGT, in four , 25% loss, compared with my 50% loss (1 in 2) .

 

Unfortunately my Dyone "yells" at me when the EGT (or anything else) is exceeding preset limits or gone RS - very disconcerting, especially in the landing phase. Can turn off but returns a few minutes later.

 

Wet and very windy weather, has given me the opportunity to replace the (assumed to be) defective EGT prob - yet to fly. Will advise, if remedy correct, in due course.

 

Forgot to mention: Hobbs 230 hrs, so EGT defect not out of line with many other reports.  I would have thought technology would have delivered a longer lived prob by now.

😈

[skippydiesel]

Follow Up;

 

Test Flight Today 1 hr Hobbs .

 

All good - New thermocouple delivered its finding/sensings to the cockpit display (Dynon) - no nasty warning blaring in my headset

 

Departed early arvo. Airfield to myself. Headed south to area around Moss Vale, some lumpy air on the way 

Seemed to be chopper day, at lest 4 around Mittagong - not all on CTAF.

Air very smooth & clear, on way back north, to The Oaks - more choppers (or the same ones?) very few fixed wings. 

Great to be a pilot!!

.😈