Not trying to start a flame war here but you are only partially correct in your statement. True Q = kA (Ti-To) which describes the conductivity of the radiator. However the heat removed from the system through the coolant is Q = k * mass flow rate of coolant * temp. change of coolant (Q = km(Ti-To)
The t-stat reduces the mass flow of coolant which increases the temp of the system (the energy into the system remains unchanged; therefore if the mass flow rate decreases the temp differential must increase); this is what keeps the temp up when little heat is added to the system. If you remove the t-stat and compare coolant temps (same ambient conditions, some vehicle speed) of the same vehicle running w/o a t-stat will give you lower temps. The heat into the system is unchanged (comparing with and w/o a t-stat) yet the temps are different. It is just a balancing act between the difference in coolant mass flow rates and the coolant temperature.
Example - While on the highway with my 165F t-stat my coolant temp runs at 165F. The power required to move the car at highway speed (65 MPH) is fairly small (I'm guessing maybe 20-30 Hp). With the t-stat removed I run about 150F on a summer day. However in an application where much higher Hp is used (i.e. more heat into the system), such as on track, my coolant temperature is much greater than 165F (near 200F).
