Abstract: An engine coolant flow controlling valve for governing the flow of engine coolant to a heater core comprises a valve housing defining first and second ports for respectively introducing coolant to the valve housing from the engine and directing coolant to the engine from the housing, said first and second ports opening into said housing adjacent each other in a housing wall, and third and fourth ports for respectively directing coolant from the housing to the heater core and introducing coolant from the heater core to the housing; a ceramic valving member supported for translational movement in the housing between a first position wherein coolant flows to said heater core via the first and third ports and returns to the engine via the second and fourth ports and a second position wherein the valving member blocks flow through the third and fourth ports and coolant flows from the first port to the second port bypassing said heater core.