EGT Probe Placement

[apatti]

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,

[Ironflight]

Originally Posted by apatti

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

[apatti]

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,

[Mathew Sharp]

Originally Posted by apatti

... 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.

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.

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.

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

[JonJay]

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