[dunerocket]

To answer your second question, the added fluid volume does not increase cooling capacity. *It merely increases the length of time that it will take to heat that fluid up. *If the lines running to and from are not insulated then you would lose some heat through them, but not that much. *The surface area of all the fins in the radiator drawfs the surface area of the tubes. *I would fit the largest reasonably sized radiator and keep the thermostat. *Cover some of the radiator up in the winter if it is not getting warm enough.