The IO-550N has a different oil cooler than the TSIO.  The TSIO tends to run cool, and the IO-550N runs hot.  It doesn't seem to have as efficient oil flow through the cooler as the oil cooler on the TSIO.  Some do better than others.  Interestingly, the IO-550G (original equipment on the ES) used the same cooler as the TSIO.

 

Mike Easley

~205 in the climb, ~198 in cruise, IO-550N