Thermoviscous lubricant flow in seals and bearings is treated as a Couette flow, and a fully coupled perturbation flow, which results from waviness of the boundary, and which gives rise to uneven heat input into the solid boundaries. Differences in modes of heat transfer within the seal rings and out to the environment are separable, and determine the thermoviscous behavior of the film in a simple way. The temperature perturbation, or wave, in the film is an order of magnitude smaller than the perturbation of heat generation, justifying the assumption of isothermal and isoviscous flow.