Abstract: A cooling system for the power plant of a self-propelled forage harvester or field chopper, generally located in the rear thereof, comprises an air chamber communicating with the atmosphere through laterally disposed filter screens and water-cooling radiators and through pairs of conical half-shells disposed point-symmetrically about ventilating fans integral with a unidirectionally rotatable shaft extending longitudinally in an opening in the top wall of the chamber. The shells, rigid with a support manually pivotable about the power-plant-driven shaft, normally direct air flow through the fans from the air chamber but may be rotated 180.degree. by a vehicle operator to temporarily reverse the air flow and pressurize the chamber, thus forcing air out through the radiators and filter screens, cleaning them of clogging debris collected during normal operation of the vehicle. Sealer strips provided around the openings in the air chamber for minimizing leakage.