A closed hydraulic system (10) of the type for steering a boat including a hydraulic cylinder (18) having port and starboard sides (20, 22) and a piston (24) within the cylinder (18) moveable therebetween. A steering pump (12) has first and second fluid outlets (14, 16). Port and starboard hydraulic lines (26, 28) interconnect the port and starboard sides (20, 22) to the first and second outlets (14, 16) respectively, for fluid communication therebetween. A closed separator tank (30) separates air from hydraulic fluid. The tank (30) includes port and starboard tank line (32, 34) in fluid communication with the port and starboard hydraulic lines (26, 28) respectively. The tank (30) includes a bleeder valve mechanism for selectively allowing fluid flow in one direction from the port tank line (32) into the separator tank (30) and out the starboard tank line (34) and alternatively in the opposite direction.