Systems and methods for zero power automatic thermal regulation are provided. In one embodiment, a method for passive thermal management comprises: establishing thermal conductivity between a self-heating electronic device and a cooling fluid held within a fluid reservoir via a thermal interface; using thermally controlled expansion of the cooling fluid, controlling a length of a column of the cooling fluid extending into at least one channel extending from the fluid reservoir, wherein the channel provides a non-recirculating path for the cooling fluid to expand into, and wherein the length of a column of the cooling fluid is thermally controlled using heat absorbed by the cooling fluid from the self-heating electronic device; and selectively establishing a primary heat path between the electronic device and a heat sink interface thermally coupled to an external environment as a function of the length of the column of the cooling fluid within the channel.