Abstract: In an electric motor having an external motor cooling fan mounted outboard of one of its rotor shaft bearings, the cup-shaped enclosure for said fan conventionally has its side wall radially spaced from a part of the frame to cooperate therewith in defining an annular outlet through which air from said fan is guided axially across the motor exterior, all around the same. According to the invention, that outlet is substantially blocked, as by an arcuate air barrier strip, to convert the fan enclosure into a plenum chamber from which pressurized air is forced through the motor interior for substantially greater cooling effectiveness.