Disclosed is a nozzle assembly which includes a nozzle housing and a valve element axially slidable therewithin between a closed and an open position. The nozzle housing has a housing inlet and a housing outlet fluidly interconnected by a plurality of housing passages. The valve element has a truncated conical valve body including a conical outer surface and a concave inner surface with a plurality of valve apertures extending through the valve body. The outer surface is sealingly engagable to a valve seat formed in the housing outlet such that the flow of cooling water through the valve apertures is prevented when the valve element is in the closed position. The outer surface and valve seat collectively define an annular gap when the valve element is axially displaced to the open position such that a portion of the cooling water flowing through the annular gap may pass through the valve apertures.