AN ACR TWIN JET PIC'S RPT ON A RETURN LAND MANDATED BY THE #2 ENG OVERHEAT WARNING COMING ON WHEN CLBING 40 MI W OF PDT; OR.

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ACFT WAS DISPATCHED WITH THE 'B' LOOP OF THE #2 ENG OVERHEAT AND FIRE DETECTION SYS DEFERRED INOP. 'A' LOOP OF THAT SYS WAS WRITTEN UP AS WORKING NORMALLY AND TESTED PROPERLY ON THE GND. I SUSPECTED THE SYS HAD BEEN WORKED ON OVERNIGHT BECAUSE DEP POINT WAS AN OVERNIGHT MAINT BASE AND IT APPEARED #2 ENG HAD BEEN RUN ON THE GND. EVERYTHING NORMAL UNTIL CLBING THROUGH APPROX 31000 FT FOR A CRUISE ALT OF 33000 FT. ENG OVERHEAT LIGHT CAME ON FOR #2 ENG. PROC LEADS YOU TO SHUT DOWN THE ENG IF OVERHEAT LIGHT REMAINS ON. WE DECLARED AN EMER AND TURNED BACK TO DEP ARPT. OVERHEAT LIGHT WENT OUT. OVERHEAT LIGHT BECAME INTERMITTENT. PERFORMING FIRE TEST THE SYS APPEARED NORMAL. ENG OP APPEARED NORMAL AND VISUAL CHK OF ENG APPEARED NORMAL. DID NOT SHUT ENG DOWN; RETURNED FOR NORMAL LNDG. AFTER REACHING THE GATE; WE PERFORMED A FIRE TEST AND A FAULT/INOP TEST FOR THE MECH. THE FAULT INOP TEST DID NOT WORK PROPERLY BECAUSE THE OVERHEAT LIGHT CAME ON DURING TEST. A FEW MINS LATER THE MECH BROUGHT ANOTHER MECH TO SHOW HIM THE INDICATION BUT THIS TIME THE FAULT/INOP TEST WORKED PROPERLY WITHOUT THE OVERHEAT LIGHT COMING ON. THE AIRPLANE WAS TAKEN OTS TO FIX THE OVERHEAT AND FIRE DETECTION SYS. SOMETHING COULD HAVE POSSIBLY BEEN DONE DURING THE OVERNIGHT MAINT THAT CAUSED THE GOOD LOOP OF THE DETECTOR TO MALFUNCTION. I WILL HAVE SECOND THOUGHTS ABOUT TAKING AN ACFT IN THE FUTURE THAT HAS ONE LOOP OF THE DETECTOR INOP.