MD80 CREW HAD A SUSPECTED FUEL LEAK IN THE R FUEL SYS.

Narrative

THE R WING FUEL QUANTITY WAS SIGNIFICANTLY LOWER THAN L WING FUEL QUANTITY. WING TANKS SHOULD HAVE BEEN FAIRLY EVEN AND NEAR FULL SINCE THERE WAS FUEL IN THE CTR TANK AND THAT CTR TANK FUEL SHOULD HAVE BEEN SUPPLYING BOTH ENGS SINCE ALL BOOST PUMPS WERE ON (NORMAL PROCS). AS THE CTR TANK QUANTITY WAS NOT INCREASING; WE SUSPECTED A FUEL LEAK. WE GOT OUT THE OPERATING MANUAL AND WENT TO THE FUEL SECTION TO READ THE 'INFLT FUEL LOSS' ABNORMAL. THE ABNORMAL LED US TO INSPECT THE WING FROM THE CABIN TO CHK FOR A WING LEAK. INSPECTION OF THE R WING FROM THE CABIN REVEALED NO LEAK. ALSO; AILERON TRIM WAS INCREASING VERIFYING AN ACTUAL IMBAL. THIS LED US TO BELIEVE THAT THE LEAK WAS ENG RELATED AS INDICATED BY THE ABNORMAL. AS WE INFORMED ATC OF OUR PROB; AN ACFT HAD US VISUALLY AND RPTED THAT THEY SAW SOMETHING COMING FROM THE TAIL OF OUR ACFT. A VAPOR FROM THE TAIL THAT THEY SAID MAY OR MAY NOT BE A CONTRAIL. THIS SUPPORTED OUR SUSPICION THAT THE LOSS OF FUEL FROM THE R TANK WAS FROM THE ENG. WE PROCEEDED THROUGH THE ABNORMAL; WHICH LED US TO 'LAND AT NEAREST SUITABLE ARPT' AND THE QRH PROC 'ENG FIRE/DAMAGE/SEPARATION.' I DECLARED AN EMER WITH ATC; SHUT DOWN THE ENG; AND DIVERTED TO SIOUX FALLS; SD; WHICH WAS 90 NM OFF OUR TAIL. WE LANDED 2000 LBS OVERWT. AFTER LNDG; THE ENG AND TAIL AREA WERE INSPECTED BY CFR ON THE RWY FOR SIGNS OF A FUEL LEAK. NO LEAK WAS SEEN AND I TAXIED TO THE GATE AND PARKED.