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EGT Probe Placement

apatti

Well Known Member
While researching threads on probe placement I ran across a post that stated the closer you place the probes to the cylinder the shorter their life. I have the Vetterman exhaust. The pipe coming out of the #1 cylinder takes a turn fairly early. It looks like the best mounting spot is about 1.5" below the flange. This is less than the 2" minimum recommended in the EIS install manual. Is this mounting location going to cause early probe demise?

Thanks,
 
Is this mounting location going to cause early probe demise?

Thanks,

In my experience? Yes!

I'm sure you know this, but the most important thing if you are going to compare values between cylinders (rather than just where the peaks are) is that they all be located the same distance from the exhaust flange. About three inches worked for me.

Paul
 
Looks like I will ask my friend to weld up three holes. At $36 a pop, I'd rather not be replacing these things too often.

Thanks,
 
... This is less than the 2" minimum recommended in the EIS install manual. Is this mounting location going to cause early probe demise?
Thanks,


Thank you for bringing this issue up as it gives me a chance to share some information about probes, EGT probes specifically.

As we all know, a thermocouple is when two dissimilar metals are joined together. This causes a small micro voltage to be generated. When temperature is added, the micro voltage being sent to the instrument changes. This is how we calibrate our temperature systems.:cool:

Unfortunately different metals contract and expand at different rates. Other manufacturers make grounded probes, which lock together the metals (three) in the tip of the probe. This “locking together” of the metal does not allow for any movement when the metals expand and contact during temperature cycles under normal use. This causes the metals to work against each other, which causes fracturing of the metals in the probe tip. This means a probe failure. :mad:

What we do with our "ungrounded" probes is allow for this movement during expansion and contractions with heat cycles. We do this by insulating the two material junction in ceramic without ever going to the SS material of the probe it's self. This “pure” thermocouple junction is more accurate, more stable, less susceptible it engine ground noise, and more durable than any other probes in General Aviation. You see, there is no fatiguing effect with heat cycles. :D

Our probes can be used on any manufacturers engine temperature equipment utilizing K thermocouples for this reason.

As a note: What one other probe manufacture has chosen to do to combat indication issues, and longevity is two fold.

1. Spend through the nose on marketing praising their probes and discrediting our probes. 2. Specify their installations to be 3-4” down the exhaust tube. (Buying time here and nothing more) The “grounded” probe will fail anyway sooner or later depending on the degree of use.

We on the other hand specify 1.5” down from the exhaust flange. In the flame of the exhaust. If installed correctly, and kept tight, our EGT probes should outlast your new exhaust. Or last as long anyway.

I hope this information is found to be useful and please let me know if there are any questions.

Matt
 
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Watch your plugs

Regardless of the distance you choose, make sure you orient them so you can still get a wrench on your plugs!
 
Revival

I am reviving and old thread. I cant seem to fine a location where all probes are the same distance from flange. Number 1 has a tight bend near cylinder so I need to be 3” away. Number 3 has a boss 3” away, so it has to be closure. Here are my pipes mark with my plan locations.
I am running a G3x so will see all four at the same time.

Do y’all think these locations are ok?

Thanks in advance.

Edit: After talking with Dr Vetterman, I am going to move my #1 hole, to be like Glenn (below),the others are ok.
 

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I am reviving and old thread. I cant seem to fine a location where all probes are the same distance from flange. Number 1 has a tight bend near cylinder so I need to be 3” away. Number 3 has a boss 3” away, so it has to be closure. Here are my pipes mark with my plan locations.
I am running a G3x so will see all four at the same time.

Do y’all think these locations are ok?

Thanks in advance.

As others have said, make sure that you can maintain other stuff when the probes are installed. Removing the probes to change a plug will be a hassle.

If your probes are not the same distance from the exhaust flange, then your temps will be different, but for leaning and balancing the injectors it won't make any difference.

I don't know your installation but I would not have a problem installing a probe in a bend if that's the right place. Happy to learn from someone that this is a bad idea, but as long as the probe seats well, and the hose clamp is secure, I think it will work. Check with your exhaust supplier if they are comfortable with you installing the EGT probe in a bend before doing so.
 
Not absolute values

John

If the distance between the probes varies a bit it doesn’t really matter as it’s not absolute values we’re after but looking for when each cylinder peaks.
So if one reads 1500 and another 1480 it really doesn’t show anything. But when each probe peaks and then starts decreasing is the critical point.
Also there is no given max value for egt unless you have a turbocharged engine which might have a turbo inlet limit.
I switched to EI probes after the dynon ones failed at about 200 hours. Recently one was reading low by a few hundred degrees which got my attention. However cht’s all matched and peak egt occurred in line with the others. Turned out the probe must have been caught and was 1/2 out of its hole. Simple fix. But I felt comfortable knowing that although the reading was low the cylinder peaked at the correct time.

Regards

Peter
 
This is a Vettermans exhaust on a 390. It really is the position of the tip that is important to have the same relative to each other. This should be considered if mounting on an angle. I have no clearance issues getting to the plugs.
 

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I have mine up pretty close to the flange to get them all close to equal distant. My absolute EGTs are higher than most quote but as mentioned previously absolutes don’t mean anything. I have 1000 hours on these JPI probes and still all originals. Pretty sure I will now have a probe failure on next flight.
 
Here's a few questions. I look through the install manual but didn't find the answer and plan on replacing my probes this annual.
1) with the G3x, does it matter if the probe is grounded or ungrounded? From what I read, grounded is usually for analog instruments but not all probes seem to state which they are.

2) EI has the fast and robust probes. The universal probe says it is fast and is half the price of EI and Garmin. Any thoughts on which?
 
K Themocouple

David

If you check out the earlier post from Mathew at electronics international he answers this question
“Our probes can be used on any manufacturers engine temperature equipment utilizing K thermocouples for this reason. “

Sometimes paying more now for quality is cheaper in the long run. At least with EI probes your pretty much guaranteed a quality product.

Regards

Peter
 
Great Pictures- Really helpful

This is a Vettermans exhaust on a 390. It really is the position of the tip that is important to have the same relative to each other. This should be considered if mounting on an angle. I have no clearance issues getting to the plugs.

Thanks for the pictures; I noticed you did your #1 on a bend. I was worried about sealing when the clap is tweaking around a bend. I need to think about this some more.

Turns out the seal for the EGT probe is the fit of the probe in the #30 reamed hole. Therefore installing them on a bend is not a problem. I did mine just like Glenn did in above post. But on a bend, it is not the hole locationthat is important, but rather where the tip is inside the tube. QED
 
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Thanks for pictures

This is a Vettermans exhaust on a 390. It really is the position of the tip that is important to have the same relative to each other. This should be considered if mounting on an angle. I have no clearance issues getting to the plugs.

I noticed you ran the CHT/EGT probes and spark plug wires together.
Is that OK, or should I keep temp sense wires separate?
 
I noticed you ran the CHT/EGT probes and spark plug wires together.
Is that OK, or should I keep temp sense wires separate?

I have not had any issues. I mostly copied off of other builders who ran the wires in a similar fashion. Is it recommended not to do this?
 
I have not had any issues. I mostly copied off of other builders who ran the wires in a similar fashion. Is it recommended not to do this?

I have read some possibly "old wives tales" that spark plug wires must be kept away from everything, even each other. I've also read that this is not true even if it might have been true in the past.

I used spark plug wire holders that do keep a bit of separation between the wires, but have not been too concerned if they get close to each other. I also ran EGT and CHT probes near the spark plug wires for a few inches here and there.

So far, no issues. The only thing I can think of that might be a problem is if one of the spark plug wires cracks or breaks, it might look for a short return path via the EGT/CHT probe wiring. For that reason, I would not run spark plug wires near something like a fuel line.
 
I have read some possibly "old wives tales" that spark plug wires must be kept away from everything, even each other. I've also read that this is not true even if it might have been true in the past.

I used spark plug wire holders that do keep a bit of separation between the wires, but have not been too concerned if they get close to each other. I also ran EGT and CHT probes near the spark plug wires for a few inches here and there.

So far, no issues. The only thing I can think of that might be a problem is if one of the spark plug wires cracks or breaks, it might look for a short return path via the EGT/CHT probe wiring. For that reason, I would not run spark plug wires near something like a fuel line.

It's Never a good idea to run high voltage wires in the same bundle as sense wires if it can be avoided. (EGT/CHT run in the microvolt range)
You may get away with it but still not good practice.
 
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It's Never a good idea to run high voltage wires in the same bundle as sense wires if it can be avoided. (EGT/CHT run in the microvolt range)
You may get away with it but still not good practice.

Agreed. The effects will obviously depend on where the lower voltage wires are going, but there's a lot of modern PCB based electronics that aren't protected against that kind of induced energy. Older mechanical gauges may handle the EMI without damage, but I've seen a quite a few board components get fried because of induced voltage on signal lines.
 
It's Never a good idea to run high voltage wires in the same bundle as sense wires if it can be avoided. (EGT/CHT run in the microvolt range)
You may get away with it but still not good practice.

+1

On my 10, I ran them too close and got erratic EGT readings on two cylinders. Moved them, problem disappeared. No surprise, given their VERY low voltage signals.

These thermocouple signals are WAY more sensitive than the other stuff running around FF.

Larry
 
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Final location

Thanks for all who responded and a big thank you to Larry Vetterman for the phone call and education. Here are my final locations (as shown in the pictures). I tested them all with a heat gun and they are all correct and seem to be reading with the same accuracy, so I think I am good to go!
 

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