EGT probe distance from flange

Dorfie · #1 01-01-2016, 06:01 PM

Garmin specifies 2-4 inch below flange for EGT probe installation. The No. 1 cyl on the IO-540 allows only about 2.25 inch below the flange then there is a bend in the pipe.
Any advice or experience as to how the distance below flange effects responsiveness, accuracy and longevity? Does it matter much?
Thanks.
Johan

Kahuna · #2 01-01-2016, 06:13 PM

Quote:

Originally Posted by Dorfie

Garmin specifies 2-4 inch below flange for EGT probe installation. The No. 1 cyl on the IO-540 allows only about 2.25 inch below the flange then there is a bend in the pipe.
Any advice or experience as to how the distance blow flange effects responsiveness, accuracy and longevity? Does it matter much?
Thanks.
Johan

Really doesnt matter that much. Use a good guess for a pipe bend. You can draw a line down the pipe following the center of the pipe, and measure that if you want. Putting it on the bend is fine.

Ironflight · #3 01-01-2016, 09:29 PM

The important thing is to find a way to put them ALL at the same distance if you want to compare cyliders. The temp varies quite a bit with a very small distance change.

jjconstant · #4 01-01-2016, 11:40 PM

I did mine all at about 2 1/2" down from the flange. The only thing I hadn't realized was that the closer you are to the exhaust port you are, the more damage ocurrs to the actual tip of the probes from heat, pressure, erosion and whatever else is gong on in that punishing environment! I had to replace 3 egt probes already at 300 hrs. The symptom is sudden and rapid fluctuations in egt at a non believable low temperature, with no noticeable difference in smoothness, power or ultimately chts. First tme it happens it really gets your attention.

I think if I had put them a little further away, they may have lasted longer.

Walt · #5 01-02-2016, 05:27 AM

For reference, this is from the Electronics International Install Manual:

"The ideal location is 1 1/2", but ease of installation should prevail."

I've had my EI EGT probes at about 1.5" since the beginning with no failures (hint: all probes are not created equal).

jjconstant · #6 01-02-2016, 01:33 PM

I think my original grt probes might be less equal than others

Has grt upgraded their probes yet? Mine were new 10 years ago. I got lucky in a way, in that I got probes from both grt with the EIS, and from Mattituck. I initially went with the GRT out of worry over compatability and have been replacing each of the probes as they failed with the ones supplied by Mattituck. Any idea who made those? So far, no failures with them.

SMO · #7 01-02-2016, 02:08 PM

GRT has reasonably priced "long-life" probes with a 5 year guarantee. They are made from Hastealloy IIRC. My understanding is that for longer life you want them made from either Inconel or Hastealloy.

When I was replacing mine the research I did led me to purchase the GRT long life probes - seemed to be the right compromise. There are much more expensive probes available!

Dorfie · #8 01-03-2016, 07:57 PM

Quote:

Originally Posted by Kahuna

Really doesnt matter that much. Use a good guess for a pipe bend. You can draw a line down the pipe following the center of the pipe, and measure that if you want. Putting it on the bend is fine.

Just to be sure. If I understand correctly you are saying it is important to get the probe TIP to be at the same distance from the flange as the others that goes straight in?? So drill the hole perpendicular to the pipe so that the tips are same distance.
Thx.
Johan

rzbill · #9 01-04-2016, 05:18 PM

Quote:

Originally Posted by SMO

GRT has reasonably priced "long-life" probes with a 5 year guarantee. They are made from Hastealloy IIRC. My understanding is that for longer life you want them made from either Inconel or Hastealloy.

When I was replacing mine the research I did led me to purchase the GRT long life probes - seemed to be the right compromise. There are much more expensive probes available!

I got the standard GRT probes in the beginning. Bought 4 of the long life jobs after the first standard probe failed at around 250 hrs. Changing them out as they fail. Two of the standard probes are still OK after 500 hrs. Hmm. Maybe I shouldn't 'a said that. Watch one fail on the next flight.

Dorfie · #10 01-04-2016, 05:49 PM

Thanks for all the replies.
I drilled the holes today. The size of the EGT part that press-fit into the exhaust pipe measures at 0.130", right in between a #29 (too big) and #30 (too small) drill!! So close!! I don't have a reamer that small. What did you guys do?
Thanks.
Johan