Originally Posted by Carl Froehlich
+1. Your EGTs suggest you are flying around at full rich. Not good for your wallet or your engine (plug fouling, stuck exhaust valve, etc.).
If you CHTs remain that low at leaner mixtures it suggests you have excess cooling - so excess engine cooling air drag.
Mike Busch has a video discussing the “Sweet Spot” for CHTs, above 350 but below 400 (Lycoming engines). He explains why cooler CHTs is not always better.
Mikes logic is that sticking valves are caused by lead deposits on the valve stem. This flies completely in the face of the standard remediation method for sticking valves, which is too remove deposits from the valve guide. If Mike were correct about deposits on the stem reducing the clearance, cleaning out the valve guides would not resolve the sticking valve problem and would instead require that the valve stem be cleaned of deposit build up. Given that the standard fix, which seems to work universally, is to remove deposits from the guides without touching the valve stem, It seems extremely unlikely that he is correct in his hypothesis. He covers a lot of correct science about lead deposits, but I believe he misplaces it in identifying the root cause of sticking valves, which a long history has been shown to be due to build up in the guides.
Lycoming further supports this logic, as they recommend cleaning out the guides, NOT cleaning off the valve stem, if the stem to guide clearance is reduced below specs. If this were an ineffective approach to the problem and instead required valve stem cleaning, I am confident that we would have figured it out by now.