What was found
AT CRUISE ALTITUDE, 33,000 FT, HAD RT JETPIPE OVHT INDICATION. RAN QRH, SECURED ENGINE, & RETURNED TO DEPARTURE. RED CAS INDICATION STAYED ON AFTER ALL EMERGENCY ACTIONS ACCOMPLISHED. SWAPPED EXHAUST NOZZLE ASSY & ZONE B PYLON FIRE-DETECTION CONTROL UNITS. PERFORMED OPS CHECK & FAULT DIDN'T FOLLOW. RETURNED TO ORIGINAL LOCATIONS. PERFORMED GVI & NO FAULT FOUND. PERFORMED RESISTANCE CHECK & FOUND EXHAUST NOZZLE ASSY SENSING ELEMENT OUT OF LIMITS. CHECKED RESISTANCE OF PYLON SENSING ELEMENT & RESULT WAS WITHIN LIMITS. INCOMING PART CHECK SATISFACTORY. INSTALLED A NEW SENSING ELEMENT. PERFORMED OPS CHECK SATISFACTORY. WORK DONE IAW AMM 26-11-04.