Calibrated bypass structure for heat exchanger

A by-pass conduit for a stacked plate heat exchanger is disclosed. The by-pass conduit is formed by first and second plate members that each have a substantially planar central portion surrounded by an offset peripheral flange, the peripheral flanges of the first and second plates being sealably joined together and the planar central portions of the first and second plates being in spaced opposition to define a bypass channel. A flow restricting structure provides a fluid restricting barrier in the bypass channel, the flow restricting structure defining a calibrated by-pass passage that regulates the flow of fluid through the bypass channel.