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Old 07-29-2012, 05:01 PM
yankee-flyer yankee-flyer is offline
Join Date: Jun 2009
Location: Dayton, OH
Posts: 821
Question High EGT Alarm--Need Rotax Guru input

912 ULS Rotax installed in an RV-12. 22 months/127 hours on the engine. Everything OK at 100-hour inspection.

This morning on taxi out the left EGT readout spiked up to 2000+ degrees in just a couple of seconds. I shut everything down waited a minute and re-started-- everything normal. Flew 1.2 hours to a family reunion with no problems and the airplane sat fro almost 4 hours.
About 15 minutes after takeoff the left EGT reading spiked; I reduced power from 5200 to about 4200 and the temp started to drop slowly and then instantaneously dropped to normal, Back to cruise power/altitude (Density altitude 7700 and yes, the fuel flow was reading 5.9 again) and about 15 minutes later the same thing happened, including instantaneous return to normal ( the display actually blinked as it changed) I noted the conditions as follows:
EGT L 1265 then up to 2079
EGT R 1240 (Normally seem to read 25-50 deg cooler than left side)
RPM 5200
MP 22.7/8 (reading fluctuates rapidly in the decimal digit)
Oil Pressure 68
Oil Temp 214
CHT L 187
CHT R 186
OAT about 55 F

There was NO CHANGE in engine sound, power output, manifold pressure, RPM, or anything else I could see while the EGT was climbing (less than 10 seconds from baseline to 2079), 3-4 seconds to instantaneous drop).

Same thing happened a third time with me keeping a close eye on alternate airports along route.

Then during descent from cruise altitude to home base at about 4500 RPM it spiked again. Pulling power all the way back had no affect, Going to FULL power brought an instantaneous return to normal.

I can't think of any mechanical problem that would cause this other than something hanging up a carb float (lean mixture) but it happens most often after 10-15 minutes at constant power setting>Need input on what to look at. Loose EGT probe? Loose connection back at the firewall? Or ????

On the positive side, at about 1025 Lbs gross weight, take off from a not particularly manicured grass strip at 2500 density altitude was not more than 1000 feet ground roll-- what a change from my AA-1!!!l

Thanks guys-- need to fix this before flying Young Eagles Saturday.

Wayne 120241/143WM
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Old 07-29-2012, 05:46 PM
Dave12 Dave12 is offline
Join Date: Oct 2010
Location: Elkton, Md.
Posts: 1,164

Wayne, I had the exact same problem at 100 hours. I replaced the egt probe and life is good again. It is a Dynon part and I think it is either 30 or 60 dollars.
Proud Dad of a Navy Corpsman
FMF "Devil Doc" 2nd Marines
N588DF RV12 #336 Sold
N73DF RV12 #244 Flying
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Old 07-29-2012, 06:13 PM
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Tony_T Tony_T is offline
Join Date: Dec 2008
Location: Seattle, WA
Posts: 1,040
Default High impedance connection?


Your thoughts about a loose connection are sound reasoning. I would be suspicious of a poorly crimped spade connector first. The Dynon is very susceptible to high impedance connections. I doubt if there is any way the readings could spike like you describe because of an actual engine problem. You should be able to make a visual check of the crimps on the connections as a first step.

RV-12 #202 -- Flying
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Old 07-29-2012, 06:25 PM
Hal-san Hal-san is offline
Join Date: Nov 2007
Location: Spanaway, WA
Posts: 191

I had a similar problem and found that the left and right EGT wires were crossed in the connector to the D180. After I found out I was chasing the wrong side, I corrected the wiring and recrimped the spade terminals and have not had a problem since.

Harold Irvine
N912HM RV-12 Flying.
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Old 07-29-2012, 06:59 PM
Mich48041 Mich48041 is online now
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,202

I agree with those who suspect a bad connection at the spade connectors forward of the firewall. Page 45-05 deals with their installation. I suggest replacing the spade connectors.
Joe Gores
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Old 07-29-2012, 07:59 PM
crashley crashley is offline
Join Date: Jun 2009
Location: hazelwood north vic
Posts: 155
Default temps

Originally Posted by Mich48041 View Post
I agree with those who suspect a bad connection at the spade connectors forward of the firewall. Page 45-05 deals with their installation. I suggest replacing the spade connectors.
Joe Gores
Hi if it spikes it is a thermocouple or cable fault check all the connections it wont be a real temp problem
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Old 10-02-2012, 10:13 AM
jimbower jimbower is offline
Join Date: Aug 2006
Location: St. Louis, MO
Posts: 158
Default Spike on #2 EGT

I have a Dynon D-120, and after about 58 hours on my -6A I suddenly saw the #2 EGT spiking to a high (maximum?) temperature last evening. As soon as I noticed it, the reading went back to normal, but repeated this process several times before I got back to the airport and shut down. The CHTs were all good, and after shutdown the EGTs were all pretty much in the same ballpark.

I never really suspected anything other than a probe or wiring issue, but it's very comforting to know others have experienced the same problem.

Jim Bower
St. Louis
RV-6A N143DJ (flying since 9/2011)
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Old 10-02-2012, 05:21 PM
N223JH N223JH is offline
Join Date: Apr 2008
Location: Boerne, TX
Posts: 226
Default Occam's Razor

Wayne, Been through this... Find the EGT connectors on top of the engine. Pull 'em apart. Check for corrosion. Put some dielectric grease or vaseline on them. Now get two pairs of needlenose pliers and firmly push those connectors together. If this doesn't work you may have to replace the spades.

flyin' 140 hours
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Old 10-03-2012, 03:05 PM
yankee-flyer yankee-flyer is offline
Join Date: Jun 2009
Location: Dayton, OH
Posts: 821
Default New Probe

Checked, crimped, and even replaced one terminal without success. Called Dynon and ordered a new probe. Installed that and everything's been fine for 15+ hours. Apparently those probes aren't real durable.

Wayne 120241/143WM
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Old 10-03-2012, 03:25 PM
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Dvalcik Dvalcik is offline
Join Date: Jul 2011
Location: Ellsworth, ME
Posts: 671

I have a GRT instead of the Dynon, but also had to replace one after a short period of time. I agree they are sensitive and can be damaged easy. Donít know how much the Dynon's were, but the GRT were not too expensive, just the hassle factor
Belfast, ME
2016 VAF Supporter

RV12 #568 EAB - 805 build hours (11 months)
* Started Sept 15, 2011
* 1st flight 8/30/12
* 40 hr phase 1 complete 10/5/12
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