An oil cooling system and method are provided for use with respect to a lubricated mechanical system within a bypass configured gas turbine engine. A surface cooler is fluidly linked to the lubricated mechanical system to receive oil from the lubricated mechanical system for cooling and reuse. In an embodiment, the surface cooler is mounted on an existing surface within the bypass airflow path of the bypass configured gas turbine engine to provide effective cooling while avoiding the introduction of additional aerodynamic disturbances in the bypass path. In an embodiment, the surface cooler is mounted on the fan casing or on a fan exit guide vane.