Retract EGT Probe?

by John Austin

Apr 25

I've got a few hours on my new Gen 4 and my #4 cylinder EGT is consistently high relative to the other 5 cylinders.  Ironically, the #4 cylinder is also one of my coolest cylinders, running about 250-275F.  (I've checked to be sure #4 is not lean-of-peak, which would cause it to run cool.  I've also checked for induction leaks and swapped probes to verify the probe is not faulty.  I borescoped the cylinder and the valves look normal and the plugs' colors are identical to adjacent cylinders.)

At this point, I'm thinking that my EGT is falsely elevated due to the probe's position on the exhaust manifold.  This position was pre-drilled by Jabiru - they pop a stainless rivet in the hole and then you drill it out if you're installing an EGT probe.

I saw "somewhere" on the 'net that someone calibrated an EGT to make it closer to the others by putting a washer under the probe's head to back it out of the manifold a few mm.  As we know, the exhaust gas temp varies greatly both in distance from the exhaust valve and where the probe lies within the diameter of the exhaust manifold. 

Why would I want to do this?  Mike Busch, the "Savvy Aviator" guru, has for years preached that absolute EGT values are meaningless because of the multiple variables involved and the CHT's are more of a valid indicator of cylinder/valve stress.  However, EGT changes relative to other cylinders' EGT's can be used for early detection of problems and or diagnosis of problems.  I simply would like to lower the absolute (meaningless?) EGT value so that it is more in-scale with the others and not so distracting.

I envision putting a small stainless washer under the probe's head to see what will happen - can't see any harm unless it causes a leak, which will be easy to detect.  Anyone ever heard of this mod or knows how effective it is in changing the indicated EGT?

John

N750A

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    John Austin

    Update: I emailed GRT Avionics (the probe vendor) and tech support quickly replied.  They said that it was perfectly acceptable to put one or more washers under the probe's head to back it out of the manifold a bit and observe the effect on indicated temperature.  I'll probably give that a try the next time I have the lower cowl off.

    John

    Apr 25

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      Jimmy Young

      I’ve got a similar situation on my C-90 #1 cylinder. It is the coolest cylinder in standard cruise mode, but always has EGT temps around 100° to 150° higher than the other 3. I understand the logic Mike Busch has stated regarding the ease of having temp variations due to probe positions, and have never concerned myself with it. Having said that, I’d like to know how this washer experiment works out, it would make it easier to spot any trends developing with engine health. 


      Congrats on getting a Gen 4 engine, I was not aware you had done that. I plan to fly up to the Sept. Zenith gathering this year, hope to see you there.

      1

      Apr 26

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        John Burns

        For the longest time on my Gen 4 I had one cylinder that would alarm EGT on climb out.  Lower the nose and all was well.  I used all of the normal tricks, clock the carb, flow divider from Nick, changing carb jets.  Each change helped extend the time before the alarm, but it still had the issue.  Suddenly last summer after about 100 hours on the engine the problem went away.  My fuel economy has also been improving as I have reached 150 hours.  I have no real explanation except to think that the engine took some time to settle in.  Oil analysis does not show any abnormal wear metal and everything else is good.  Just my recent Gen 4 experience.  I look forward to hearing more about your results.

        1

        May 5