Abstract: A diesel fuel nozzle restrictor includes an attachment flange, nozzle tube, at least one release arm, and closure cap. A top of the attachment flange is structured to receive a fuel cap. A bottom of the attachment flange is structured to be attached to an existing diesel fuel filler neck. The nozzle tube also extends from a bottom of the attachment flange. The closure cap is pivotally attached to a bottom of the nozzle tube. Each release arm is preferably attached to the nozzle tube at substantially a top thereof. A capture ledge is formed on an end of each release arm to restrict pivoting movement of the closure cap. An actuation projection is formed at substantially an end of each release arm. An opening is formed through the wall of the nozzle tube to receive the actuation projection. Insertion of the diesel fuel nozzle through the nozzle tube will cause the closure cap to open after the at least one capture ledge is removed from a bottom of the closure cap.