Chat,

 

The coolers have identical cooling fins but the routing of the oil in the lower section is different.  On a recent flight back from CA I was flying along side another ES with an IO-520 and the "cool" cooler.  He was showing 180 on the oil and I was showing 202.  Our CHT's were very close, maybe his were a little higher.

 

My CHT's pass 400 about the time my oil hits 220, that's in an aggressive climb in hot weather, so I'm not going to mess with my "hot" cooler for now.  I know my cooler isn't working as well as it should but I'm kind of in the mode that Paul from Aero-Classics suggested, "It ain't that bad".

 

Mike