Automotive vehicle engine cooling system comprising a three port valve comprising: a housing with three axially spaced inlet ports (12,16,22) and one axial outlet port; a first inlet port is fluidly connected with an outlet of a vehicle radiator, a second inlet port is fluidly connected with an outlet of a heater, a third inlet port is fluidly connected with an outlet of a cooling system bypass, said outlet port of the housing is fluidly connected with an inlet of a cooling system pump; a rotary valve assembly controlling fluid communication between said inlet ports (12, 16, 22) and said outlet port; said rotary valve assembly including: a shaft; a first generally cylindrical valve module torsionally affixed with said shaft for controlling fluid communication between the first inlet port and said outlet port, said first valve module controlling flow from between an external portion of said first valve module and an interior of said valve module; a second generally cylindrical valve module rotatively mounted on said shaft for controlling fluid communication between the second inlet port 816) and said outlet port, said second valve module controlling flow between an external portion of said second valve module and an interior of said second valve module, said second valve module having a coupling interface with said first valve module; and a third generally cylindrical valve module rotatively mounted on said shaft for controlling fluid communication between the third inlet port and said outlet port, said third valve module controlling flow between an external portion of said third valve module and an interior portion of said third valve module, said third valve module having a coupling interface with said second valve module,wherein said first valve module and said second valve module coupling interface has a torsional lost motion connection to cause a hysteresis in the flow rate of fluid to the heater and wherein said valve has an over temperature safety to allow flow from said first inlet port into said valve housing regardless of a position of said first valve module and said over temperature safety is provided by a housing extension which connects an auxiliary port with the radiator upstream of the first inlet port and is controlled by the temperature in said third inlet port. a shaft; a first generally cylindrical valve module torsionally affixed with said shaft for controlling fluid communication between the first inlet port and said outlet port, said first valve module controlling flow from between an external portion of said first valve module and an interior of said valve module; a second generally cylindrical valve module rotatively mounted on said shaft for controlling fluid communication between the second inlet port 816) and said outlet port, said second valve module controlling flow between an external portion of said second valve module and an interior of said second valve module, said second valve module having a coupling interface with said first valve module; and a third generally cylindrical valve module rotatively mounted on said shaft for controlling fluid communication between the third inlet port and said outlet port, said third valve module controlling flow between an external portion of said third valve module and an interior portion of said third valve module, said third valve module having a coupling interface with said second valve module,wherein said first valve module and said second valve module coupling interface has a torsional lost motion connection to cause a hysteresis in the flow rate of fluid to the heater and wherein said valve has an over temperature safety to allow flow from said first inlet port into said valve housing regardless of a position of said first valve module and said over temperature safety is provided by a housing extension which connects an auxiliary port with the radiator upstream of the first inlet port and is controlled by the temperature in said third inlet port.