An electrical submersible pump assembly has a pressure equalizer coupled to a lower end of a motor. The equalizer has a motor lubricant passage through which lubricant in the motor communicates with motor lubricant in the equalizing element. A valve element in the motor lubricant passage has a closed upper position and an open lower position. The valve element has a drive member on an upper end that mates with a shaft drive member on a lower end of the motor shaft while the valve element is in the upper position and disengages from the shaft drive member while the valve element is in the lower position. A locking feature between the valve element and the motor lubricant passage retains the valve element in the upper position and is releasable in response to rotation of the motor shaft in a selected direction.