A submersible well pump assembly has a communication path for communicating motor lubricant to an interior of a pressure equalizer. A check valve passage with a check valve leads from the communication path to a pressure equalizing chamber. A dip tube has a dip tube inlet at the check valve passage below the check valve and a dip tube outlet in the pressure equalizing chamber. The dip tube is filled with motor lubricant to retard migration of well fluid from the pressure equalizing chamber into contact with the check valve.