Engine cooling seems to be an almost universal challenge to alternative engine users.  As I make small changes to my system I am more and more convinced that it is all the details and parts of the system that makes it a success or failure, not just one key part like size of the heat exchanger.   This conclusion was recently reinforced while working with another RV builder who has an almost identical cooling system (at least in verbal description, I haven't actually seen it) to my own.  Mine is working OK, his is overheating.

Last week's cooling experiment result was a surprise to me.  My RV-8 cooling system was already adequate but on climb out on hot days the oil temps would still be at redline with full power and that makes me feel like I have less margin than I'd like.  Hoping to loose a couple of degrees I decided to smooth the sides of the exit duct where the air has to go around the 3/4" flange of the firewall for about 2" on both sides of the exit.  I had already increased the radius of the stock firewall at the top of the exit.   Just adding a small piece of sheet aluminum to the sides of the exit was the change.  Took about 10 minutes to make and install.  They form a ramp to guide the air over the firewall flange so the air doesn't get tripped up going over it.  At least that was the theory.   The improvement was all out of proportion to what I expected.  Don't know the exact number of degrees but it's enough to make a world of difference in my comfort when I'm scanning the gauges on climb out.  

This obviously  is not a magic answer to all cooling problems but I think it illustrates that any one of many details can be the weak link in your cooling system.  

Tracy