CHT troubleshooting

On a post condition inspection test flight last week I had wonky readings for CHT #5.

The reading would drop very low, then return to normal, and repeat - intermittently and unpredictably.

In flight lean of peak mag check was totally fine. The engine ran normally the entire time, with no noticeable roughness or anything.

The EGT for that cylinder never changed.

I have the G3X data but am at work tonight and cannot download it.

I'm pretty sure this is a sensor issue. Do these probes have a failure mode, or is this more likely a wiring issue?

Looking for troubleshooting ideas before I head out to pull the cowling.

Thanks
Thomas

Maybe wiring..

I had one that was doing crazy stuff. Re-crimped the connection and it work fine for a bit. Then started doing it again. Re-crimped it worked fine and then started doing it again. I cut of the crimp connectors and soldered the wires. No issues since...

jeffkersey said:

I had one that was doing crazy stuff. Re-crimped the connection and it work fine for a bit. Then started doing it again. Re-crimped it worked fine and then started doing it again. I cut of the crimp connectors and soldered the wires. No issues since...

Click to expand...

+1

First place to look for that symptom would be in any connections between that CHT probe and the instrument/EMS. They are usually solid core vs stranded and the crimps can loosen up if not done properly. VERY low voltage transmission, so ANY issue in the crimp can cause this.

Larry

Just to close the loop:

I pulled the top cowl, moved the sheath on the wires and checked the connections.

These are a screw together fitting, crimped to the wires. The crimps were solid, looked good, and didn't pull apart. However, the screw had backed out about 1/2 way, even with the star type lock washer. I retightened it; I think at next oil change I may shrink wrap all of these with clear shrink tube.

Or, would loctite be ok?

Curious if this is common.

A new lock washer and blue lok-tite should be fine.

The Alcor brand of probes include a fiberglass sleeve that is supposed to be installed over the joint.

B

Yup - the sleeve is there, just pulled back (you can see it in the pic).

It isn't tight enough to keep the screw from backing out, though.

A little heat-shrink over the joint shouldn't harm anything. Use the basic stuff, not the adhesive lined. The later is a P.I.T.A. when you need to remove it.