MD80 DISPATCHED WITH A QUESTIONABLY ACCURATE FUEL GAUGE AND SUBJECTED TO FUEL CONSUMING REROUTES AND VECTORS DECLARES A FUEL EMER TO INSURE PROMPT HANDLING AT DEST.

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OUR DAY BEGAN AS WE MET THE INBOUND CREW. THE FO TOLD ME THAT 2 UNITS OF AILERON TRIM WAS NEEDED DURING THE ENTIRE FLT. ON HIS ORIGINATION PREFLT HE FOUND THE AILERON TRIM AT 2 UNITS. THEY DID NOT WRITE UP THIS PROB. I PROCEEDED TO THE AIRPLANE; CALLED MAINT AND WROTE UP THE DISCREPANCY IN THE AML. IT WAS DETERMINED BY MAINT THAT OUR R MAIN FUEL QUANTITY GAUGE WAS READING HIGH (LESS FUEL IN TANK THAN WHAT WAS ON GAUGE). OUR ORIGINAL RELEASE HAD US ARRIVING IN ZZZ1 WITH 8190 LBS OF FUEL. MAINT TOLD ME THAT THE GAUGE WAS 500 LBS OFF; SO I CALLED DISPATCH AND RECEIVED AN AMENDED RELEASE FUEL OF 25900 LBS. WE WOULD HAVE 7700 LBS OF FUEL AT DEST. THE FLT WAS UNEVENTFUL UNTIL AFTER FIX #1. AT THAT POINT WE WERE 2 MINS AHEAD OF FLT PLAN AND 200 LBS DOWN ON THE FUEL. WE WERE GIVEN A RERTE FROM ATC THAT ADDED ABOUT 115 MILES AND 15 MINS FLYING TIME. WE ADVISED DISPATCH AND FUEL BURN WAS CALCULATED. WE WOULD NOW ARRIVE AT ZZZ1 WITH 5300 LBS OF FUEL. WE ASKED FOR AND RECEIVED 2 MINOR SHORTCUTS ON OUR RTE. WE ALSO ADVISED ATC THAT WE WERE IN A MINIMUM FUEL SITUATION AND COULD NOT ACCEPT VECTORING. LATER WE WERE 1 MIN AHEAD OF FLT PLAN AND 400 LBS DOWN ON FUEL. WE WOULD NOW ARRIVE AT ZZZ1 WITH 4900 LBS OF FUEL. WHEN ATC NEEDED TO GIVE US SEVERAL VECTORS FOR TFC INTO THE ZZZ1 AREA; WE ADVISED AGAIN THAT WE WERE MINIMUM FUEL AND WE COULD NOT ACCEPT ANY VECTORING. ATC SAID HE NEEDED US TO COMPLY WITH VECTORS; SO WE DECLARED AN EMER. WE WERE GIVEN PRIORITY; BUT STAYED ON THE ARR; SINCE IT NEARLY LINED UP WITH THE ARPT. WE USED A 250 KT DSCNT SPD TO SAVE FUEL. DUE TO THE SHORT TIME REMAINING IN OUR FLT AND BEING BUSY; WE WERE NOT ABLE TO CONTACT DISPATCH WHEN WE WERE CLRED FOR THE ILS INTO ZZZ1. THE LNDG WAS UNEVENTFUL AND WE TAXIED TO THE GATE. WE PARKED AT THE GATE WITH APPROX 5700-6100 LBS OF FUEL; BASED ON DIFFERING FUEL STICKS. I BELIEVE THAT IF WE HAD COMPLIED WITH THE EXTENSIVE VECTORING AND MANEUVERING TO LAND ON RWY; WE WOULD HAVE BEEN IN SERIOUS TROUBLE WITH LOW FUEL AND AN INOP FUEL GAUGE.