An electric motor/generator cooling mechanism is presented. The cooling mechanism includes a hollow cooling jacket having an inner and outer coaxial surface, where the inner surface defines a generally cylindric cavity for receiving a stator in heat transference contact with the inner surface, and the outer surface has a cast spiral groove section with jogged cooling passages. The disclosure includes an outer case having one or more inlet ports, an outlet port, and a vent for purging air, cooling fluid flowingly encased between the cooling jacket and the outer case, flowing through the jogged cooling passages, and a flanged end surface on an end of the outer case for boltingly connecting the cooling jacket to the outer case.