EGT Problem ?

[drhunt]

Today I flew 3 one-hour+ legs. On the first two, I noticed that in cruise, about an hour into each flight, my EGT started to oscillate about 100 degrees, always cooler than the temp I had been running. The engine was running smoothly and I didn't notice any changes on the tach, oil pressure, oil temp or fuel pressure. I isolated mags with normal results. Everything was normal on the last leg. I have an Archer III with a Lycoming O360 A4M. I would guess that the problem is in the EGT but thought I'd check here to see if anyone has any other insights.

 

[bbchien]

Today I flew 3 one-hour+ legs. On the first two, I noticed that in cruise, about an hour into each flight, my EGT started to oscillate about 100 degrees, always cooler than the temp I had been running. The engine was running smoothly and I didn't notice any changes on the tach, oil pressure, oil temp or fuel pressure. I isolated mags with normal results. Everything was normal on the last leg. I have an Archer III with a Lycoming O360 A4M. I would guess that the problem is in the EGT but thought I'd check here to see if anyone has any other insights.

Fraying #18 gauge sensor wire, just proximal to the o= fitting where it connects to the probe. The engine vibrates, shakes the heck out of the wire, which eventually breaks strands. When it lets go, you'll get Zero CHT.

You can check out the shaking by varying RPM. The needle oscillating changes rate in keeping with engine rpms. Very easy fix, if I'm correct.

 

[wsuffa]

I'm with Bruce. Likely a probe or probe wire. Most likely a frayed/shorting wire, but possibly one that's going open. If that probe has push-connectors in it (if it's a JPI or similar, it probably does).

I've had similar issues on a JPI traced to a loose connector.

 

[drhunt]

Thanks guys, I'll take a look and check with my shop.