Abstract: A bypass valve includes a valve body containing a spring loaded valve member. The valve body includes first and second interconnected bores respectively connected to the outlet and inlet of a fluid pump feeding a fluid function. A valve member slidably disposed in the valve bores includes a cylindrical portion and a frusto-conical portion cooperating with the first and second bores to provide a predetermined pressure drop across both portions at a first flow rate with cold fluid and at a second flow rate with hot fluid. The spring is set so as to allow fluid to bypass from the pump outlet to the inlet until the predetermined pressure drop is exceeded.