What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

EGT probe longevity?

Carlos151

Well Known Member
Friend
Last couple of times I?ve powered up my Dynon FlightDEK D180 my number 3 cylinder EGT shows over 2000 degrees. Obviously the indication is not correct since the engine is not even running. About 30 seconds after starting up, the temperature comes down to within 20 degrees of the other cylinders and all indications on the ground and in flight are well within limits. The probes all have 375 hours on them.
I?ve got a Mattituck IO360 with a Plasma III for the top plugs and a Pmag for the bottom plugs. I routinely run LOP.

My question: what is the average life expectancy of Dynon EGT probes?
 
I typically have to replace an EGT probe every other year. 4 probes in 8 years, or one every 200 hrs.
 
I have JPI system, not Dynon, but a reference.
1200 hours on original probs.

FYI...hangar mate installed a new JPI some years ago....not long after, he had a probe fail "high"....JPI replaced it.

Seems I read somewhere Dynon works with universal probes.

Also, there used to be a ongoing debate between EI and Jpi on who's probes were better.
 
My EGT probes lasted life of engine and exhaust system. In other words, I ran my EGT probes for 2,200 hour. I replaced them and the exhaust system when cylinders were replaced on the engine.
 
My probe issues were always the connections

My current probes have over a 1000hrs --- but, in the past, if I ever had erratic temp indications, it was always connections/wiring issues.

Ron
 
I had several connection problems with my Dynon probes. The indications would jump around toward high temps or x out. One replacement probe consistently indicated 200 degrees or so low. Replaced the replacement and back to normal readings, inline with the others.
I had other probes in other planes go several thousand hours. Eventually the probe itself wears away in the exhaust stream and quits working. Some sooner, some later.
 
Thanks gents for all the replies. Looks like as always, you get what you pay for. The higher priced probes are reported to last longer so it's a trade off on how frequently you mind changing probes.

EI probes, no issues.

Looks like the EI and JPI probes are of a higher quality if you look at the reported longevity. At 3-4 times higher price than Dynon, and as easy as it is to replace an EGT probe, I'm not sure I can justify that price difference. At almost 400 hours and this is the first issue I've had.

but, in the past, if I ever had erratic temp indications, it was always connections/wiring issues.

All connections and wiring have worked flawlessly from day one but I will definitely check the connectors next time I remove the cowling.

Eventually the probe itself wears away in the exhaust stream and quits working. Some sooner, some later.

This was my initial thought. Routinely see all EGT's in the 1350 range +/- 20 while in cruise LOP. Just like any other sensor in that kind of heat, they'll eventually wear out.

Just lost my first Dynon probe at 500 hours. Had same indications as you more or less. FWIW, my probes are about 2-2.5? from the exhaust flange.

Can't remember what distance I mounted the probes at but all four temperatures match up nicely so I'll take that as a good mounting location for all.
 
I have 1000 hours on my engine with Dynon probes and D120. I replaced one EGT maybe 100 hours ago and am starting to see flashes of "shock cooling" on one CHT that probably indicates it is about to go bad. I'm happy with the longevity. For reference, my EGT probes are about 4" down on the exhaust pipe.
 
JPI probes still functioning at over 900 hours with them 2? from flange to have them all equal distance. That gives me peak EGTs of 1475 to 1550 deg F, which is were I run 90% of the time (I know I am old school not running LOP). Talked to JPI at OSH one year and asked about the high EGTs and he said only issue is probes may go bad early than normal. 900+ hours and doing fine.
 
We have been producing a variety of EGT probes over the last 20 years or so. At a guess, probably well over 200.000 so far.

On some installations the probes last "forever". on others not - even if similar installations.
There are a whole host of possible failure causes.

Yes, quality plays a role - up to a point. In principle you look for the quality of the thermocouple cable - the materials are dictated as far as the cores go. Electrical insulation - some probes I have seen use fiberglass, others a mineral fiber. The mineral fiber withstands higher temps - but is brittle and damages easily. The fiberglass can work - but only if the probes construction inside does not rely on it (probes can use ceramic sleeves inside which also makes them much stronger at high temps).
Typically 316 stainless is used - that's perhaps the best overall material. Wall thickness is again a compromise between strength and speed of reaction. Typically 0.4 to 0.5mm is the norm.

Most failures we have investigated are down to the cable itself - mechanical damage usually due to the cable flexing with engine movement. Just like bending a piece of fence wire repeatedly - the internal cores do not like that and break. Can also affect the insulation - that breaks and the cores short out or to the usual metal sheath of the cable. Most often the break is around the entry point to the probe itself (usually a spring is used to assist this area).

Then there are other issues. Fortunately more rare: Complete probe disintegration. When we get one of those - first thing we do is see if a magnet sticks to the probe. If it does - you have rust in the fuel. Rust particles instantaneously melt in the combustion flame (in particular with turbo changed engines), loosing the oxygen in the process so you have tiny liquid blobs of iron exiting the combustion chamber - usually by the time they get to the EGT probe they are ready to melt onto the surface. Layers of this get added over time (the probe diameter gets bigger). Trouble with this is iron has a very different thermal expansion compared to 316 stainless. The iron actually rips the probe to pieces over time. I have seen this a few times over the years - the probes totally disintegrate or if caught early enough you see them bent (sometimes at crazy angles) - this due to the iron coating not being even on all sides.
The "magnet check" shows quickly what you are dealing with - also on any of the iron you can scrape off the probe.
So that is one to watch out for - it will destroy any probe - no matter how much you paid for it.

Probes typically can go up to 1200 degrees C for short times - at this temperature they glow white. Very high flow velocities can conceivably bend the probes as they will be weak. I have not seen this happening with our probes though (but it's not impossible).
At normal combustion temperatures (non turbo, low revving engines) the probes are pretty much bullet proof - they barely even glow a dark red.
High revving engines (like Rotax's 912 range) can have much higher temps (the probes glow a nice satisfying red at up to 850 degrees C redline). Above that it gets orange and eventually white hot.

If you have a probe fail - investigate why it failed - first look at the cable very carefully (in particular where it enters the probe). If that all looks good - take a dremel with a cutting disk and cut the probe open lengthwise - the thermocouple itself should be close to the tip. Anything interesting to see there ? Of course if the probe is mechanically damaged then look elsewhere.

Rainier
CEO MGL Avionics
 
We have been producing a variety of EGT probes over the last 20 years or so. At a guess, probably well over 200.000 so far.

On some installations the probes last "forever". on others not - even if similar installations.
There are a whole host of possible failure causes.

Yes, quality plays a role - up to a point. In principle you look for the quality of the thermocouple cable - the materials are dictated as far as the cores go. Electrical insulation - some probes I have seen use fiberglass, others a mineral fiber. The mineral fiber withstands higher temps - but is brittle and damages easily. The fiberglass can work - but only if the probes construction inside does not rely on it (probes can use ceramic sleeves inside which also makes them much stronger at high temps).
Typically 316 stainless is used - that's perhaps the best overall material. Wall thickness is again a compromise between strength and speed of reaction. Typically 0.4 to 0.5mm is the norm.

Most failures we have investigated are down to the cable itself - mechanical damage usually due to the cable flexing with engine movement. Just like bending a piece of fence wire repeatedly - the internal cores do not like that and break. Can also affect the insulation - that breaks and the cores short out or to the usual metal sheath of the cable. Most often the break is around the entry point to the probe itself (usually a spring is used to assist this area).

Then there are other issues. Fortunately more rare: Complete probe disintegration. When we get one of those - first thing we do is see if a magnet sticks to the probe. If it does - you have rust in the fuel. Rust particles instantaneously melt in the combustion flame (in particular with turbo changed engines), loosing the oxygen in the process so you have tiny liquid blobs of iron exiting the combustion chamber - usually by the time they get to the EGT probe they are ready to melt onto the surface. Layers of this get added over time (the probe diameter gets bigger). Trouble with this is iron has a very different thermal expansion compared to 316 stainless. The iron actually rips the probe to pieces over time. I have seen this a few times over the years - the probes totally disintegrate or if caught early enough you see them bent (sometimes at crazy angles) - this due to the iron coating not being even on all sides.
The "magnet check" shows quickly what you are dealing with - also on any of the iron you can scrape off the probe.
So that is one to watch out for - it will destroy any probe - no matter how much you paid for it.

Probes typically can go up to 1200 degrees C for short times - at this temperature they glow white. Very high flow velocities can conceivably bend the probes as they will be weak. I have not seen this happening with our probes though (but it's not impossible).
At normal combustion temperatures (non turbo, low revving engines) the probes are pretty much bullet proof - they barely even glow a dark red.
High revving engines (like Rotax's 912 range) can have much higher temps (the probes glow a nice satisfying red at up to 850 degrees C redline). Above that it gets orange and eventually white hot.

If you have a probe fail - investigate why it failed - first look at the cable very carefully (in particular where it enters the probe). If that all looks good - take a dremel with a cutting disk and cut the probe open lengthwise - the thermocouple itself should be close to the tip. Anything interesting to see there ? Of course if the probe is mechanically damaged then look elsewhere.

Rainier
CEO MGL Avionics

Rainier, thanks for the detailed analysis you provided.
The probe in question is still providing intermittent false indications that last about 7 seconds after starting up so I'm not in a hurry to inspect or replace it anytime soon. I will however remove it and inspect it as you suggested along with all of the wiring to that probe. I have a new probe in hand to replace the questionable one and I strongly suspect that it is a wiring issue from the probe. I'll be inspecting the spring area at the entry point closely. These wires are the most likely to catch on the cowling Skybolt fasteners when installing or removing for access so it's possible that may be the cause. Now I'm curious to cut the probe open. Will report back if I find anything.

Once again, thanks for the detailed insight into the life of an EGT probe.
 
I have six Dynon supplied probes. One failed at about 1100 hours the rest are still going fine at 1800.

Probes can be damaged by being pushed into holes with insufficient clearance or at a funny angle. They fail some time later, and nobody ever knows why. I suspect they fail from mechanical damage at installation. Just a hunch.
 
I have six Dynon supplied probes. One failed at about 1100 hours the rest are still going fine at 1800.

Probes can be damaged by being pushed into holes with insufficient clearance or at a funny angle. They fail some time later, and nobody ever knows why. I suspect they fail from mechanical damage at installation. Just a hunch.

Thanks David. When you say ?sometime later? what timeframe does that fit?
I installed all four probes using the same Dynon approved and published instructions 375+ hours ago. Now, one probe is acting up, so when you say ?sometime later?, is that 300 hours, 3000 hours, or 30,000 hours? With that kind of statement, IMHO, you?re pretty much saying the probe can fail at any time. Well, that?s pretty much true of any man made mechanical or electrical item.
 
Back
Top