CHT Probes

Never have used any sealant on CHT probes. Have not seen it called for in any Lycoming or Continental service or OH manual

Don Broussard A&P/ IA etc
RV9 Rebuild in Progress
57 Pacer
 
You're not trying to seal the threads against pressure, so I would say "no". But you DO want to be able to remove the probe if and when it fails (one of mine just did after 170 hrs.). For that reason, I use nickel anti-seize on those threads. I removed my failed probe today and although tight, it came right out.