Have you tried running the fan full time? In a normal acting cooling system the electric fan/radiator are sized so that they can remove more heat and faster than the engine can produce it. Therefore, ram air can keep the coolant temperature under control most of the time.
In this case, the radiator is sized for an engine fan turning all the time (and close to the radiator) so by letting the coolant get to 185 before the fan comes on, the block and head have heat soak that is above the curve before you start the fan.
The fan on all time can't overcool because the thermostat will take over.
