MD80 FLT CREW HAS A FUEL IMBAL AFTER TKOF; DECLARES AN EMER AND RETURNS FOR LNDG.

Narrative

I TRIED TO TRIM THE ACFT AND HAD TO USE AN EXCESSIVE AMOUNT OF TRIM. AS WE WERE CLBING OUT WE WERE TRYING TO DETERMINE EXACTLY WHY WE NEEDED SO MUCH TRIM (L AILERON DOWN) WHEN I NOTICED THE L FUEL GAUGE READING 1800 LBS. THE R FUEL GAUGE READ APPROX 9600 LBS AND THE CTR TANK HAD MORE THAN 8000 LBS. I RELAYED THIS TO THE FO AND I DECIDED TO OPEN THE FUEL XFER VALVE AND ENSURED ALL FUEL PUMPS WERE ON SINCE WE WERE NOT CERTAIN AT THIS POINT EXACTLY WHAT WAS HAPPENING. I FELT THAT WITH ALL PUMPS ON THAT I WOULD HAVE POSITIVE FUEL FLOW TO BOTH ENGS WHILE WE TROUBLESHOT THE PROB SINCE THE CTR PUMPS HAVE GREATER PUMP OUTPUT THAN THE MAIN TANK PUMPS. I REQUESTED THE FUEL LEAK/FUEL XFER CHKLIST AND STATED THAT WE NEEDED TO GO BACK TO ZZZ AND THAT WE SHOULD DECLARE AN EMER. HE COMMUNICATED OUR NEEDS TO ATC AND WE REQUESTED CFR EQUIP TO BE STANDING BY. I MADE A PA TO THE PAX STATING THAT WE WERE RETURNING TO ZZZ FOR A MAINT PROB. THE FO STARTED RUNNING THE CHKLIST WHILE I WAS FLYING THE ACFT AND COMMUNICATING WITH ATC. AS THE FO WAS RUNNING THE CHKLIST HE STATED THAT WE WEREN'T LOSING FUEL. BY THIS TIME WE HAD STARTED TO TURN BACK TO ZZZ. I TOLD THE FO TO DISCONTINUE THE CHKLIST SINCE I FELT THAT WE WERE CLOSE TO FINAL AND I NEEDED HIS HELP FOR COORD AND ANY POSSIBLE ASSISTANCE IF I NEEDED HELP CTLING THE ACFT. I ALSO INSTRUCTED THE FO TO RELAY TO THE FLT ATTENDANTS WHAT WAS HAPPENING AND TO CALL RAMP AND HAVE THEM CALL DISPATCH TO TELL THEM THAT WE WERE RETURNING TO ZZZ WITH A FUEL IMBAL. WE COMPLETED THE APCH AND LNDG AT ZZZ WITH NO OTHER PROBS NOTED. WE LANDED OVERWT AT APPROX 138000 LBS.