This paper presents a sensorless bifilar wound permanent magnet brushless DC (BW-PMBLDC) motor fan for automotive engine cooling applications. The key is to incorporate the bifilar winding design into the conventional half-wave PMBLDC motor. Due to the perfect flux-coupling effect between bifilar winding, a regenerative capability is developed so that the trapped energy in the conducting winding during the turn-off period can be re-dumped to DC source through the other winding in the bifilar pair, hence effectively promoting the energy efficiency and repressing the voltage spikes. Moreover, the complementary scheme developed between the bifilar wound phases enables bipolar excitation on the unipolar converter topology. Therefore, the BWPMBLDC motor cannot only offer the advantages of full-wave motor in efficiency, voltage spike reduction, and low torque ripple, but also retain the advantages of simplicity and robustness of unipolar converter topology. Both simulation and experimental results are presented to validate the feasibility.