GRT EGT Probe failures

Today pulled the EGT probes on my -9A and discovered the nature of the failures that occurred at the start of my cross country trip 2 wks ago.

These probes are the standard EGT probes provided by Grand Rapids Technology with their engine analyzer system.
Service to date:

252 hrs in service (3 yrs)
Mounted 2" from cylinder flange
Fuel: 100LL w/ Alcor TCP treatment
EGT's rarely read over 1400 Deg.
Local flying is ~50% power ROP
Cruise flying is ~60% power LOP

Whatever materials these are made of is not OK.

I ran ECI International System EGT probes in my Long-EZ for 22 yrs and never had a probe failure.

Needless to say, they don't make them like they use to! I'd suggest pulling 1 or 2 probes at annuals to verify they are OK.

Disappointing - yes. I've got 1675 hours on my GRT probes on the Val, and they are still going strong (they'l start failing tomorrow of course...). But mine are at 3" from the exhaust flanges, so they live in a little less hostile environment. Two inches is pretty close, but having placed a lot of probes, I understand how sometimes you don't have much choice in order to find a place that works on all cylinders.

I have 410 hours on mine and they looked very good as of about 20 hours ago. Mine are mounted 1.75" from the flange and just as Paul said, they will probably fail in the next flight.

I had a couple go out around 400 hours and ended up replacing all 4 at the time, but I'd think we'd get more out of them.

I bought these probes in 2008 and they first ran in 2010. There is clearly a metallurgy problem here, because this just isn't right.

I'll have replacement probes here Friday, so will be interesting to see how they fair. These original probes have a 2 yr warranty.... tells me the manufacturer "knows something" about longevity (or lack of).

GRT says they are getting "better" probes with a 5 yr warranty, but won't have any for a couple weeks. I've told them to get me on the wait list and ship them also when they come in.

I'm sorry to hear you're disappointed with your EGT probes. I think the distance of 2 inches from the cylinder had a lot to do with the failure. At that distance, the probes are still in the flame, so they will wear faster. The Long Life probes are made of a different material, so they should serve your installation better.

GRT directions ...

If I recall correctly, the GRT installation directions said to place them as close to 2" as possible. All my paperwork is at the hangar, so I can 't substantiate that recall at this moment. I say this because mine are 1.75" from the flange, and I would have no reason to place them there other than specific instruction from the mfgr.

2" is with in the recommended placement. It's the exact same placement I used on my Long-EZ for 22 yrs and over a 1000 hrs with ECI probes and never had a failure. "Deek" has 2940 hrs on Alcor probes with no failures. As I said before, this is clearly a materials problem. Has nothing to do with GRT, but the manufacturer of these particular probes.

The real question is, would Alcor/ECI probes be compatible with the GRT EMS?
When you look at the price difference between Alcor/ECI probes and GRT probes, it makes you wonder if you get what you pay for.

Upon failure ...

Just out of curiosity, what did you see on the display when they failed? Did the readings go way high or low? (It will be good to know if mine fail in similar fashion.)

They start out erratic with 50-100 deg swings then ultimately fail low (0-100 Deg indicated) when the two wires are no longer touching. Two of these failed within 2 min of each other as I was making an IFR departure. Fortunately was still VFR when it occured so was able to return to the airport to investigate and make sure something serious wasn't going on. Was a little unsettling when it happened because I was initially concerned it could be cracked/broken exhaust pipes.

700 hours

Mine failed at 700 hours, 5 years.
Mounted 2" per the installation instructions
The replacements are supposed to be better material. 1100 TT in 8 years and no issues so far on the replacements.

Gary

Looks like I got one @ 160 hrs.
Noticed erratic reading 3 flights ago and it failed on last flight.
I took it out today for a look. The junction is not visible. It looks like the best of the 4 in the OPs first post.

I'll be ordering one of the long life units (and a spare) tomorrow.

Lost my first "Short-Life" EGT probe Dec 2013

2 yrs since first flight.
124.5 Hrs.
2.5" from cylinder head(recommended distance and not much choice with bends).
During initial climb out, EGT #3 went from 1250F-900F, intermittent afterwards.
Outer sheath showed slight erosion but still intact.
I indicate 65% pwr or less, 10-30 LOP and 10.5 gph in cruise.
100LL Only.

Tested #3 probe when new...1.6 ohms between red/yellow
1.5 ohms from red-gnd or yellow-grd
Produced 28 mVDC with MAPP gas flame @3.5" from probe heated dull red
When heated red-gnd and yellow-gnd resistances went from 1.5 to 55 ohms.

Tested intermittent probe upon removal...1.4 ohms red-yellow
0 ohms red-gnd, 1.0 ohm yellow-gnd
Still produced 28 mVDC
When heated red-gnd went from 0-45 ohms and yellow-gnd went from 1.0-0 ohms.

Ordered two "Long-Life" probes from GRT to have a spare. Replaced and all is well for now. #3 EGT has always been one of my higher readings and is about 20F higher than the previous probe, possibly why it went first. If I had the money, I would have replaced all six.

Poor material choice for probe junction and sheath. I do not understand the selling of a "Short-Life" probe in any aircraft EIS kit and would have liked the opportunity to upgrade.

my experience

I have 1150 hours on my RV7a since it was licensed in 2007 and have never replaced a GRT EGT probe. I believe I placed the probes at 5 inches from the flange. I must have missed those instructions and I suppose they will all fail now that I made this post.

tommylewis said:

I have 1150 hours on my RV7a since it was licensed in 2007 and have never replaced a GRT EGT probe. I believe I placed the probes at 5 inches from the flange. I must have missed those instructions and I suppose they will all fail now that I made this post.

Click to expand...

5" is good.

1. Position the probe 2-8 inches from the cylinder.
2. Although not critical, it is preferable to position all probes the same distance from the cylinder.
3. If possible, position the probes so that they are mounted on a straight (not curving) portion of the exhaust manifold.
The hose clamps fit slightly better on straight portions of the manifold.
4. Position the hole around the manifold so that the probe does not interfere with the cowl, and takes into
consideration practical needs related to maintenance (does not interfere with the access to the oil filter, etc.), inspections, or probe mounting.

Mine are in the same locations as Tom's, 5" inches below exhaust port, same engine as he has. 950 hrs so far. I had to replace 4 of them so far, #1 twice. All of them had the tips burned off. Go figure!

Martin Sutter
Building and flying RV's since 1988
EAA Technical Councelor

The Valkyrie has the probes about 2 and 3/4" from the flanges and all original probes are still working at 1701 hours....

That's sure to jinx them!

Paul

My originalGRT latest 250 hrs. Replaced withe a set from these folks. The sensor Connection.com. Working well after 25 hrs. Very high quality inconel construction made in USA reasonable price. Bolt in compatibility