The basic numbers so far:

 

 I got 2 degrees of oil cooling with something like 20 - 30 GPH of fuel flow through heat exchanger.

 

 Temperature rise in the tank was on the order of .1 degrees (lets say it was .2 for sake of argument)

 

We need about 40 degrees of oil cooling, about 20 times what I got in the experiment.  Also means we need 20x the fuel flow or about 500 GPH (8 1/3 GPM).

 

Assuming this means a temp rise in the tank of 20 x .2  or 4 degrees, that implies that there is a huge margin of safety here.   And this was only using one of the two tanks.  If it was required, I'd be happy to utilize both tanks.

 

I will be the first to admit that this sounds too good to be true.  I must repeat the experiment to verify the basic numbers.

        You didn't mention the fuel exit temperature (from the heat exchanger). Did you measure that temperature?

        Of course, you would not want to use the high-pressure fuel pump to move 8 GPM.