CHT probe failure modes

Today I had what appears to be a run away CHT on climb out. After a quick reduction in MAP and max fuel flow I limped around the pattern to return. Both the run up before and after the incident showed no problems.

First step in troubleshooting, where was the human last... well, I had just remounted CHT probes #2 and #4.

I'll borescope and pull the plugs tomorrow but given the quick astronomical CHT reading is there a chance this is a probe failure?

https://www.savvyanalysis.com/flight/2070957/2dae95d6-4ecf-4aea-9eab-551e227ba128 CHT +402 degrees in 11 seconds with no change in EGT?

It is a probe or more likely a loose probe crimp, check the probe terminals and terminal crimps.
If it was an injector getting plugged you would first see high EGT followed by high CHT.

Rob Hickman
N402RH RV-10

I think it is impossible for a cylinder to physically rise from 322F to 750F in a matter of seconds and repeat similar cycles over the next 2 minutes or so. I absolutely agree that you likely have a loose connection. To test a potentially failing probe, swap it with an adjacent cylinder and observe if the erratic behavior follows the probe.

CHT filtering

I felt it was the probe but that was a longer LP filter than I had expected on the sensor. I'll check the wiring and connections.

Thanks!
JD

I had a CHT probe (bayonet type) go intermittent on me; It would spike up to unbelievable values. When I measured the DC resistance, it was ~10 ohms IIRC when a good one was only 3 ohms. After doing a "pull test" on the lead crimps and making sure the pins at the back of the display were intact, I just shrugged and bought a new probe. That fixed the problem. IMHO, the simplest thing here is to just replace the probe. If that's not the problem, then you'll have a $100 spare. (Mine failed after 150 hrs.)

the probes are basically 2 types of wire twisted together. If they go wonky it is invariably because of a bad connection somewhere.

Sounds Familiar

All this sounds familiar. At around 100 Hrs # 2, 3, & 4 CHTs went ballistic sometimes up to 450, which really catches one's attention fast. Usually I go 25" / 2500 at around 700 ft. Makes no difference... the CHTs still climb. EGTs and Oil Temp are rock solid in the green.
I've replaced the baffle material, opened the area behind #3, installed the Anti-Splat Cowl Flap - all to no avail those bloody CHTs are still going into the 430 zone.
When I take the cowl off this week to begin the painting process, I'll check the crimps. Wouldn't think three CHTs would go wonky at the same time, but who knows...