A locking valve stem cap system includes a sleeve, a valve stem cap, and a rotation tool. The sleeve is configured to threadingly engage a valve stem, with a portion of a threaded region of the valve stem protruding into a cap receptacle thereof. The valve stem cap is configured to be inserted into the cap receptacle of the sleeve and to threadingly engage the portion of the threaded region that is located within the cap receptacle. The rotation tool is configured to facilitate rotation of the valve stem cap when the outer periphery thereof is substantially surrounded by the sleeve, thereby facilitating tightening or loosening of the valve stem cap relative to the sleeve. Methods for installing and removing the valve stem cap system from a valve system are also disclosed.