CRITICAL ACFT EQUIP PROB INDICATED. DIVERSION TO ALTERNATE CARRIED OUT IN B-727-200 FREIGHTER.

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I WAS THE FO ON FLT FROM PHL TO ABY. THE B727-200 HAD A LOWER AFT BODY OVERHEAT INDICATOR LIGHT ILLUMINATE DURING THE CLB TO FL310. WE ASKED ATC FOR A LEVEL OFF AT FL270 WHILE WE RAN THE EMER CHKLISTS. WE ACCOMPLISHED THE EMER CHKLIST IN ITS ENTIRETY AND COULD NOT ISOLATE THE OVERHEAT INDICATION. WE RAN THE CHKLIST A SECOND TIME AND COULD NOT DISCOVER WHAT WAS CAUSING THE PROB. WE HAD A PHONE PATCH TO MAINT AND FLT DISPATCH GOING ON DURING THIS TIME. GIVEN THE FACT THAT WE COULD NOT DETERMINE WHICH ENG IF ANY WAS CAUSING THE INDICATOR TO STAY INTERMITTENTLY ILLUMINATED; WE CHOSE TO DIVERT TO RDU FOR MAINT RATHER THAN CONTINUE ON TO OUR DEST OF ALBANY; GA; APPROX 50 MINS AWAY. WE COORDINATED THE DIVERT WITH FLT DISPATCH AT SDF AND DECLARED AN EMER WITH RDU APCH CTL. WE HAD AN UNEVENTFUL LNDG AT RDU. THE EMER WAS TERMINATED AFTER THE CRASH/FIRE/RESCUE PERSONNEL CHKED THE ACFT OVER AND DIDN'T SEE ANY PROBS. WE LEFT THE PLANE WITH THE MAINT PERSONNEL AT RDU AND DEBRIEFED THE RESCUE DEPT. THE ACFT HAD A PREVIOUS MAINT WRITE-UP CONCERNING A PREVIOUS LOWER AFT BODY OVERHEAT CONDITION WHICH HAD BEEN CORRECTED BY HAVING A CLAMP TIGHTENED. BECAUSE WE COULD NOT ISOLATE THE PROB AND THE MECH DIDN'T INITIALLY SEE ANY AREAS WHERE A BLEED AIR LEAK MIGHT HAVE BEEN PRESENT WE MAY HAVE HAD A PROB WITH THE INDICATION SYS ITSELF AND NOT A REAL BLEED AIR LEAK PROB.