Originally Posted by RV10inOz
From memory......Lycoming publish a number well below 200dF and TCM 225dF.
Interesting that TCM with their water cooled engine (a jacketed version of their normal engines) set the temp at 225.
I found this in the IO 390 operation and installation manual, P.18
For maximum service life of the engine maintain cylinder head temperatures
between 150°F. and 435°F. during continuous operation.
Thanks for the reminder to go back to the manual for guidance !