sudden drops in temperature every 20 minutes on pit probe, any idea whats going on?

I am trying to reverse sear a prime rib and I am getting this weird behavior where every 15-20 minutes the temperature drops significantly as if the lid was opened (and the lid open behavior starts up). Any ideas what could be going on? the temperature recovers but its a bit strange. Any thoughts on what this could be? This is on a Kamado Joe which is pretty well sealed, so seems pretty unlikely the temp is actually dropping so much. i have the pit probe 3-4" above where the meat is on a wooden skewer. I did a 10+ hour cook of some beef ribs yesterday and dont remember seeing this behavior at all, though I also wasnt looking very closely.

EDIT: looking at my graph yesterday I confirmed I didnt seem to have the issue. I have a few drops, but i'm guessing those are when I actually had the lid open to put on more meat/etc. I had a good 5 hour block where there were no temp drops at all after I put the final pieces of meat on.

Moisture dripping on the probe or fire?

If you are using a thermocouple pit probe (particularly a cheap one) you might want to take apart the connector and make sure the wires are screwed down tight. I had a similar problem once and it was due to loose wires in that connector.

Interesting. I had the same issue on my Cook yesterday. I have not had this in the past. I use Thermoworks thermocouple and my connection at the plug are just fine. The only thing I did was update to the .hex file dated 4/09 just the evening prior to my cook. The drop was way to fast to be a blower/damper issue. I hope I am not loosing a new thermocouple. Could there be an issue with the 4/09 update?

I've kept up with snapshot firmware and haven't seen any TC dropouts, not sure what is in the 4/09 release. Maybe try the snapshot?

I have had a thermocouple on the latest hex running for the last couple days with no drops.

The smooth recovery curve seems a bit odd for a software bug or a bad wire. It looks like what I would expect from a sudden cooling of the probe and then it coming back to temp. Water in some form would be my guess. Try it with clear skies and no meat on the grill.

That's a really good point, Matt. If it were some sort of flaky connection it would drop and then immediately return to roughly the same temperature. If it drops off and then smoothly recovers it seem more like something is cooling the thermocouple instantly then it warms back up. I'd be looking for something that's actually causing the measured temp to drop, like something touching the probe or moisture or something.

The 4/09 snapshot and firmware is just the fix for switching between low temp and high temp readings, which if it were being flaky would show up as a step function as it switched from one reference to the other. It wouldn't make it drop then slowly recover.

Thanks I’ll try it out maybe this weekend again with no meat and see if it reoccurs. The weather was nice on Sunday when I attempted the cook. 50-60 degrees and clear skies. I have a thermoworks thermocouple probe with alligator clip at the end which I had clipped to a bamboo skewer I stuck into my prime rib, about 4” above the meat.

Your rig makes it sound unlikely that there was water cooling your pit probe, however, Matt has a good point. The way the graph recovers gradually does make it seem like the probe is cooled down and recovering temp rather than abruptly kicking in and out due to a bad wire or solder joint or whatever.

You could place another probe in the pit and see how that one tracks during these events to give you a bit more information.