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New engine; CHT2 is the black sheep

wjb

wjb

Well Known Member
Hi All,

First engine start last weekend ... and have been poring over the data from the EMS. I found that CHT2 is the black sheep ... about 10% cooler than the other three, though they read the same value at room (hangar) temp.

I've built a jig to test the CHT2 + CHT4 probes against a hot plate, and found that the track fine - both probes read the same temp from the plate up to 350F (where my heat gun rand out of heat) -- doesn't' seem like it follows the sensor.

Given it's a new engine (XIO-360-M1B, Van's standard), I checked the fuel flow at the injectors (Full rich and full throttle, 30" MAP) per the Lyc and Airflow docs. All injectors were putting out the exact amount of fuel (very happy to see BTW)

I'm still curious why this one is the black sheep. Still was that way today while doing some idle circuit adjustments. Test were done in calm air, cowling off. No CHTs were harmed in the process (< 325 F always)

Is this a typical variation, or indicative of some sort of issue? Engine data below.

log_20200329_123851_KHAF_cht2-X2.jpg


Thanks!

-Bill
 
CHT troubleshooting

Did you swap that probe with another one, to see if the low temp follows the probe or stays with the cylinder ?
 
jakej said:
Did you swap that probe with another one, to see if the low temp follows the probe or stays with the cylinder ?
Click to expand...

I did a test where I put CHT2 and 4 on the same hot plate .. they measured the same. Didn't do a on-engine swap yet.
 
wjb said:
I did a test where I put CHT2 and 4 on the same hot plate .. they measured the same. Didn't do a on-engine swap yet.
Click to expand...

Bench checks for this problem is not the best solution- checking on the engine does 2 things (mostly) when swapping probe position 1. Confirms if the probe is the problem or 2. Could show if the connector is an issue - we’re talking millivolts here so a poor crimp or connection could have an impact.
As Jetmart said, 25deg is not a big issue either.
 
jakej said:
Bench checks for this problem is not the best solution- checking on the engine does 2 things (mostly) when swapping probe position 1. Confirms if the probe is the problem or 2. Could show if the connector is an issue - we?re talking millivolts here so a poor crimp or connection could have an impact.
As Jetmart said, 25deg is not a big issue either.
Click to expand...

Thanks; I'll do an on-engine swap next run.
 
Leave the sensors where they are (CHT 2 on 2....)

But switch CHT2 and CHT4 connections.

Now CHT2 temp will be on the display as CHT4 (and vice-versa)



Another test is too switch the sensors between cylinders with correct connections (cylinder 2 will be using CHT4 sensor and be on display as CHT2)


Final test is to switch the connections again.... (cylinder 2 using CHT4 sensor, on display as CHT4)


From this, you should be able to figure out if it's the cylinder, sensor or connections............
 
This is a ground run, cowling off? Low power? Put the cowling on, fly, then come back if you have issues. So far there’s no obvious problems.
New engine? Keep these ground runs to a minimum.
 
Last edited:
As a ground run . . .

Bill, No disrespect, but I think this is a waste of time. 1. 25F is not unreasonable AND it is a very short time running. You really need flight velocity to know what is happening here.

I am as picky as anyone you would find, but not at this point and under the operating conditions.
 
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