REFLECTOR: EGT probe

Dave Philipsen velocity at davebiz.com
Thu Oct 31 19:38:25 CDT 2013


First thing we should clarify is that the EGT probes are not bayonet 
probes.  Those are for the CHTs. The EGT is usually a thermocouple that 
is inserted into a hole in the exhaust manifold and it's usually held on 
by a hose clamp. Generally, we are not concerned about EXACT temperature 
reading from EGT probes because the temperature varies greatly depending 
on exactly where the probe is mounted.  I wouldn't necessarily be 
terribly worried about a 200 degree difference between two probes.  The 
CHT readings are much more accurate since each probe is placed in 
exactly the same position and the nature of these probes tends to be 
more precise.

You could easily test the probe by dipping it in a cup of boiling water 
which should read about 212 at sea level.  You could also try warming it 
up slightly with a propane torch.  You should be able to get it up above 
1000 degrees pretty quickly.  In fact, you could probably just warm up 
the outside of the exhaust pipe with a torch right near the probe 
without even removing it.  You should be able to get it to warm up to a 
few hundred degrees pretty easily.

Also, if your EGT was reading 190 and it was correct, you could probably 
touch the #1 exhaust pipe without too much discomfort. My guess is that 
you will discern that the pipe is too hot to touch before you get that 
close.

Dave Philipsen
Velocity STD FG
N83DP

On 10/31/2013 4:06 PM, Lou Stedman wrote:
> Lately I have been getting some odd readings for my #1 cylinder EGT. I 
> have a JP Instrument Classic 4 cylinder gauge. My egt reading on my #1 
> cylinder has been lower than the other three cylinders ever since I 
> had my cylinders done. I noticed that the temps of the other three are 
> running about 1350 while the #1 is running about 1150. Today I 
> installed a new aux. fuel pump. I started the engine (io-360) to check 
> my installation. Because I was at idle on the ground, the temps were 
> running about 940 on #2,#3, and #4. The temp on #1 was 190. My first 
> guess is a bad bayonet probe but I don't know how to check it. I could 
> just order a new one but they are a bit pricy. The engine runs smooth 
> and the cht reading on that cylinder is right in line. Can anyone tell 
> me how to test it?
> Lou Stedman
>
>
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