Abstract: A sealed, immersible, fast responding, coaxial thermocouple assembly and mounting arrangement thereof, for fast temperature reading of high flow rate liquid streams in mixing valves comprising an insulated first-metal wire and a surrounding dissimilar second-metal tube, the second-metal tube is crimped at a first end over a stripped extremity of the insulated first-metal wire to form a large surface area, sealed thermocouple junction, shaped as a radial array of fins axially extending along a tip portion of the thermocouple assembly. A collar ring holder and elbow mounting arrangement is maintaining the thermocouple assembly longitudinal axis principally in the direction of the flow of the liquid stream axially flowing along the tip portion and at least an additional substantial portion of the thermocouple assembly length.