A COMMUTER LTT RETURNS TO BOS WHEN THE CREW PERFORMS AN ENG SHUTDOWN. THE R ENG'S INTERSTAGE TURBINE TEMP GAUGE WAS FLUCTUATING OUT OF NORMAL RANGE AND TRIPPED THE OVERTEMP WARNING LIGHT TO 'ON.'

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CLBING THROUGH 10000 FT; ENRTE FROM BOS TO DCA; I NOTICED THE R ENG INTERSTAGE TURBINE TEMP FLUCTUATE CONSIDERABLY. I POINTED THIS OUT TO THE CAPT (PNF). AT THIS TIME THE GAUGE STARTED SHOWING TEMPS WELL OUTSIDE NORMAL OPERATING RANGE AND THE OVERTEMP LIGHT CAME ON. I BELIEVE IT WAS JUST AN INDICATION PROB; BUT SINCE THERE WAS NO WAY TO KNOW; WE ELECTED TO DO A PRECAUTIONARY SHUTDOWN. WE INFORMED THE CTLR OF THE SIT WHO VECTORED US FOR AN ILS TO RWY 4R IN BOS. WE THEN PERFORMED ALL APPLICABLE CHKLISTS AND LANDED THE ACFT WITHOUT FURTHER INCIDENTS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE FO CALLED BACK TO CONFIRM THAT THE ACFT WAS AN SF340. HE HAS BEEN ATTEMPTING TO FIND OUT FROM MAINT THE CAUSE OF THE GAUGE READING AND LIGHT BUT WITHOUT SUCCESS. HE HAD RECENTLY FLOWN THE SAME ACFT AFTER THIS EVENT BUT THE LOGBOOK WAS NEW SO NO INFO COULD BE OBTAINED FROM THAT SOURCE. HE STILL BELIEVES IT WAS THE GAUGE BUT HAS NO REAL PROOF THAT IT WAS. CALLBACK CONVERSATION WITH RPTR ON ACN 393698 REVEALED THE FOLLOWING INFO: RPTR; PIC; STATED THAT THE GAUGE MOST LIKELY WAS THE CULPRIT. IT HAD VIBRATED FIRST; THEN OSCILLATED 3 TIMES; THE FIRST TIME SETTING OFF THE OVERTEMP LIGHT; FINALLY GOING TO A 'ZERO' READING. THE PIC DID NOT FOLLOW UP WITH MAINT ON THIS EVENT. HE DID SAY THAT THE SF340 TENDS TO HAVE CANNON PLUG PROBS IN GETTING DIRTY. THIS OFTEN IS THE CAUSE OF MANY GAUGE PROBS. THE FIX FOR THAT IS TO SQUIRT THE PLUGS WITH SOME WD-40.