Lyc IO-360 CHT low on #1

This is a strange thing for me. I replaced two EGT probes (#2 and #4, burned out), didn't touch anything else. But the first flight after the replacement, the #1 CHT is showing about 60deg lower than the rest. The CHT curve is shown below. I had a few more flights after that, all showed similar trend. It started ok, when reducing power, the #1 CHT drops. EGT looks normal, engine is running fine. I will swap the CHT probe next time I get to the hangar to see if it's probe issue. But wonder if anyone has seen this and have a good explanation. I don't believe the cylinder is actually that cold, but can't explain the data. Thanks!

They are tracking well early and late. What was the plane doing in the middle? Perhaps in a level cruise? If you could discuss the flight profile during this capture, it would help.

yes, it was cruise when #1 CHT showed about 60deg lower. The flight profile is pretty typical. Full power take off, get to altitude, set cruise power and fly around, then come back and land. Nothing unique. Before it first showed this, CHTs on all cylinders are tracking well with no more than 20deg spread.

Given that you made a change, and it changed behavior, I think your on the right track for swapping probes. The increased airflow at cruise may be effecting an electrical connection that may have been impacted by your changing out some other probes. Although to be honest, its behavior should be more erratic. Swap cht probes and report the results.

Probe issue

Had a chance to swap the CHT probes for #1 and #3 cylinders and flew the aircraft last weekend. Now the #3 CHT is reading low. New CHT probe is on the order. But I am surprised by the short life of EGT and CHT probes (around 175 hrs).

What kind of probes are you using? Alcor?
Maybe I should buy some spares...

Just a thought - do you have extension leads connected to the probe? If they are crimped to quick connects or in some other way connected to the extension wires try replacing these connections and also ensure both connections are located close by each other.
Since there are dissimilar metals used in these connections it is possible that if one joint is at a different temperature to the other this may introduce a bias in the reading.

EI (Electronics International) has a new type connector for EGT/CHT leads. No more crimps and quick disconnects. It is a small barrel with a screw that squeezes down hard on the wires. An improvement, IMHO.

I pulled this from the EI website: "If an Engine Monitor is only as good as its probes then a probe is only as good as its connector. That’s why Ron and EI’s engineering team developed EI’s proprietary OLC-1 connector. The OLC-1 connector greatly increases reliability and reduces installation errors as compared to traditional type connectors."

Here is a link to the OLC-1 connector: http://buy-ei.com/portfolio/olc-1/

Very easy to install, as well. I was able to solve some intermittent issues by replacing my old crimp-connectors with this one.

I buy my thermocouple wire directly from Omega which is way cheaper and silver solder the extensions. i have had no issues on my Jidel in 200+hrs.