The performance characteristics of a radiator are analyzed and it is shown that the heat transfer and the isothermal air-side pressure drop can be presented quite generally in graphical form for any number of tube rows, ambient conditions, water flow rate, core size and a particular fin pitch. Provision is also made to determine the non-adiabatic static pressure drop based on isothermal results. In addition a method is presented whereby an “optimum” core thickness, taking into consideration fan power and core mass, is predicted.