As I recall, there was a discussion on this list about the various
types of oil coolers for Lycoming engines and their effectiveness.  I
have an IO-540 and I see that Aircraft Spruce sells Stewart Warner,
Aero Classic (the one I bought), NDM and Positech.  What was the
result of the discussion?

Gary,

 

Nothing beats the more expensive S-W for cooling efficiency.  Check the S-W web site for specs.