A removable cooling mandrel assembly for a rotating control device for use in a drilling system. The present disclosure provides an outer swivel housing enclosing an elongate passage and connected to the uppermost end of an upper housing of the rotating control device. An inner swivel mandrel is mounted in the elongate passage of the outer swivel housing for rotation relative to the outer swivel housing and may be connected to an RCD mandrel of the rotating control device to which the outer swivel housing is connected. A tubular cooling mandrel extends from the inner swivel mandrel out of the outer swivel housing to reduce operating temperatures thereby increasing bearing performance and life and seal life.