Thorp Air Command - T18.net

Yesterday I was flying along minding my own business; I had been in the air for about an hour. All instruments were reading normal. Oil PSI 80, oil temp 190 cyl. Temp. 300. rpm2400. Alt 6,500 ft and leaned too 1,375.

The EGT climbed too 1,425 (not normal) so I richened it up a bit and needed to start my decent for landing. Normally at this point I have trouble keeping heat in it but this time the EGT did not what to come down until I was throttled way back on the base leg.

This morning I had the same scenario, everything started out normal and all numbers remained normal except for the EGT. This time I had a little more time to play with it. I could lean until it stumbled at around 1,500 and richen it up a bit like you do, but could not get the EGT below 1,400 until well into my base leg.

I know that these numbers are not that bad but it is behaving differently than normal (normal is easy to run rich at 1,350 or less and it will cool too as cool as 1,200 on decent)

The only thing that has changed is we are finally getting some fall weather around here.



Brent

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http://www.dixiefriedfabrication.com/

Howdy Lou - I get the same thing and have to watch it descending - I only have a single probe - #3 cylinder - replaced it last year so fairly new - about 40 hours on it - I just keep a good eye on it, and occasionally get caught with a stumble and have to richen up - I don't know what else to do other than get a gauge with 4 probe capablilty, yet I hear that one of the hardest things to get tuned with carb'd lycs is the induction/fuel air mixture and hence the different burn efficiencies in the cylinders and uneven EGTs. Other than putting in a new probe, or tuning the induction,(including making sure the carb is operating at peak efficiency - mine has just been rebuilt) I think it's one of the things we live with.
Of course, I acquiesce to those of superior power plant knowledge.

Most inexpensive engine temp gages read the difference between the probe end and the connection end, thus the reading can and will vary with the OAT. Use them as a relative temp and not as a true temp. When leaning, watch for the peak and adjust accordingly. Once the baffling has been optimized, the cylinder head temps really only tell you if you are getting too hot on climb-out on a hot day.

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Bob Highley
N711SH
SN 835
KLAL

Hey Brent,

Just a few quick thoughts...

If you have a single EGT probe and all of a sudden it is reading higher than normal, you might want to check your intake tubes for a possible small leak. It could even be that it doesn't start sucking a little air until the engine warms up.

Bob is exactly right about cheap EGT gauges - for example Westach. With all thermocouple temp gauges you have at least one "hot" junction & one "cold' junction. However, higher quality gauges will have circuitry to compensate for changes in the ambient temperature at the gauge itself, providing proper wiring practices are followed. The thermocouple wire should be the same materials (metals) as the thermocouple (TC) itself, with no other wire type (i.e. copper) spliced in between the gauge & the TC. Any connectors should also be special ones made of the same materials. Any connections made with dissimiliar metals will create another junction that will generate a small amount of electricity & affect the accuracy of the gauge reading of course. If one of those junctions was in the engine compartment you could really see a large amount of temperature change & hence variable reading/accuracy.

It's a shame that "cheap" gauges, and sometimes poor wiring practices are prevalent in aircraft instrumentation, & pilots have just come to consider it "normal". I don't. However, I guess that usually with EGT you're just looking for a relationship to peak readings anyway, and actual numbers may not be as important to you.

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

80% of my gauges are Westach...engine instruments . So far they are working as advertised and I am very happy. They are made in the USA as compared to the knock off look alike Falcon/ISS gauges made in Commie Land . I think part of the problem folks have is in the wiring . Not a proper ground, improper crimps on the terminals, bad splices, using non compatable wire with the units...as John suggested ( cheap pilots) . Also not using matched sending units with the gauge . BOOM! "Matched" sending units...I have them for my oil pressure and fuel pressure gauges.

RB

Brent,
This topic has gotten me to thinking a little. Discounting the possibility of a gauge problem, I'm not so sure that my suggestion of a possible induction air leak is correct. I'd sure like to hear from any of you guys regarding that. Another thing that comes to mind though is a possible bad spark plug or wire, etc. on the cylinder with the all of a sudden higher EGT issue. At a certain point, higher EGT actually relates to more unburned fuel leaving the combustion chamber and burning in the exhaust pipe. I think you can demonstrate this by noting the rise in EGT when running on only one mag versus both, causing a less efficient burn. Anyone care to comment on this thought? Check your plugs/wires.

Rich - I love your gauges... please tell them that no insult was intended.

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

I did snug up the intake tube clamps but no change. I will check the plugs and wires.

Now keep in mind this is the first bird with an EGT that I

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http://www.dixiefriedfabrication.com/

Make sure your gage wires go through the firewall in their own conduit. I nearly declared an emergency on my first flight (way back when) because my CHTs approached 500 degrees. Turns out, the wires were bundled with the alternator wires and the induced current affected the temp gages. Make sure your wires are all separated.

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Bob Highley
N711SH
SN 835
KLAL

John Evens : None taken . My gauges are happy right where they are ! I still say in most cases the problems are due to improper installation or just not knowing that bundling of the wire groups may cause a problem...like in Bob's case . I ran all my engine instrument wires thru one firewall pass thru and the alternator/field/master/mag wires thru another firewall pass thru. BOOM !

RB

I think it's the weather
Cubes

Typically, during the heat of the summer I will lean to about 1350 or a little under, and all runs well just about right there, Cilinder heads will not be over 250deg. Today I drug the bird out and went for a little hop(haze was so dence you couldn't see the bugs on the windscreen) and I leaned back to 1450 or so maybe a little higher, 2500ft, it ran like a top. Cilinder heads were no hotter than they usually run which has always been on the cold side. 1450 EGT was a standard until I did some jet work, after the jet work I am able to lean or richen things up a lot better. Dan

Can't wait until you start flying in the Tule Fog ! Boom !

RB

The other thing to look at is fuel flow. During winter months, my FF goes up a lot.
Cubes

That makes sence Cubes...........Tule Fog, don't like to thread my prop through that stuff, that stuff gets dence. Dan

Update: Maybe two weeks ago I flew Renee to Hemet for breakfast, this is about a ten minute flight so I didn

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