Steve,

The attached plot shows the interaction between coolant and oil temperatures obtained on my test stand.  The oil cooler and the radiator are fed air from separate ducts and their outlet areas are independently variable.  RPM was 4000 and HP was 42 during the test.  Water T is the temperature of the coolant coming out of the engine and Oil T is oil temperature returning to the engine from the oil cooler.  With those temperatures stabilized at about 210 deg, the air delta P was 2.6 inches of water across the radiator and the oil cooler cores.

After the air flow through the oil cooler was increased while leaving the radiator air flow unchanged, the Oil T dropped from 212 to 160 deg while the Water T dropped from 212 to 200 deg.  At this time, the oil cooler oil delta T was 33 deg  and the radiator water delta T was 15 deg.

My conclusion from this is that it will be difficult to cause a significant change in the coolant operating temperature by making changes to the oil cooling part of the system.  In real life, I was a scientist.  It may be useful to run this conclusion past an engineer.  Scientists just collect data while engineers figure out what the data means and how make use of it.

From the photo of the front of the radiator inlet duct, comparing the inlet to the prop flange, it would appear that the duct inlet has an area of around 27 sq in.  Your previous information indicates an inlet area of 16.5 sq in which may be the area of the inlet through the cowl.  What sort of interface do you have between the cowl and duct?

Steve Boese