Garmin CHT errors??

[mdmba]

Ok..i need some help on this one...
i bought this plane...has Garmin 3GX touch screen
#2 is 75+CHT higher than most on climb out
my A&P moved wire 2 to cylinder head 4...and vice versa
on climb out..and flying around.."#4"...which was really the old #2...had normal temps.
so he thinks that the real #2 isn't running high CHT, but in fact, there is a error in the Garmin 3GX system...is there a calibration that is possible??

thoughts?

[Brantel]

These typically do not require any sort of calibration since the sensor is characterized within the G3X. Sounds like you have a bad probe or wiring issues but I would have to know what #2 shows on the screen after the swap to real #4.

[rvbuilder2002]

Originally Posted by mdmba

Ok..i need some help on this one...
i bought this plane...has Garmin 3GX touch screen
#2 is 75+CHT higher than most on climb out
my A&P moved wire 2 to cylinder head 4...and vice versa
on climb out..and flying around.."#4"...which was really the old #2...had normal temps.
so he thinks that the real #2 isn't running high CHT, but in fact, there is a error in the Garmin 3GX system...is there a calibration that is possible??

thoughts?

It is still early for me so I could be wrong, but it sounds like if Cyl # 2 on the screen now reads normal with it installed on cyl # 4, then it is reading correctly because it shows that cyl 4 is still normal.
What does cyl # 4 now read (with it connected to cyl # 2). If # 4 now reads 75 deg higher than the rest, then you actually have a high temp on cyl # 2.

[krwalsh]

Originally Posted by Brantel

These typically do not require any sort of calibration since the sensor is characterized within the G3X. Sounds like you have a bad probe or wiring issues.

In the instrument industry parlance what you need to do is a verification, not a calibration. This is easy to do. First, with the engine cold, perhaps first thing in the morning, verify the CHTs against the OAT probe. After a soak overnight the two should be within a few degrees of each other. Next, get a pot of water and boil it. Remove each CHT probe from the engine and put each probe tip into the boiling water. It should read 212F +/- a couple of degrees. If both of these are true, then you have verified the probe over that range. If they are not true then you should also be able to identify which probe is bad.

Note that most CHT probes have screw terminals a foot or so from the probe end. Verify these are clean, and that the color coding is matched. If the color coding gets flipped then you create another thermocouple junction at that joint, which can really impact the overall reading, especially as the in-cowl temperatures rise.

Finally, even with the spring-tip bayonet CHT probes sometimes you do not get a good seat and contact with the aluminum CHT well. Adding thermal grease to the well before putting the probe in can help.

[Ironflight]

Originally Posted by rvbuilder2002

It is still early for me so I could be wrong, but it sounds like if Cyl # 2 on the screen now reads normal with it installed on cyl # 4, then it is reading correctly because it shows that cyl 4 is still normal.
What does cyl # 4 now read (with it connected to cyl # 2). If # 4 now reads 75 deg higher than the rest, then you actually have a high temp on cyl # 2.

I had the same thought as Scott. With Van's baffles, assuming you installed the deflectors in front of #1 and #2 cylinders, it is very common to see #2 warmer than the other cylinders, because the air is deflecting over teh cylinder instead of goign through the cooling fins. This is fixed by trimming the deflector back a little at a time until you like the overall balance (between cylinders and flight conditions, i.e., cruise vs. climb). I personally like to make those deflectors removable so they are easy to trim after you get flying.

Paul