Abstract: In a self-propelled combine, an engine cooling air screen is cleaned continuously by a rotating exhaust sweep moving close to its external surface. The sweep is in the form of a duct with one side open to the screen. Air is drawn into the sweep and exhausted through the cooling fan by way of an air passage having an inlet opening in the center of the screen communicating directly with the exhaust sweep and an outlet immediately ahead of the inlet side of the fan. Power for rotation of the sweep preferably comes from the propeller action of air passing over air deflector or propeller surfaces at its extremities. Alternatively, the sweep may be driven by a more conventional bladed propeller rigidly connected to the sweep but offset rotationally from it.