B737 FLT CREW DISCOVERS FUEL IMBALANCE DURING CLIMB AT FL180 AND ELECTS TO RETURN TO DEPARTURE ARPT; SUSPECTING A FUEL LEAK.

Narrative

CLBING THROUGH APPROX FL180 I WAS STILL HAND FLYING AND WAS TRIMMING A LITTLE MORE L WING DOWN WHEN I LOOKED AT THE FUEL GAUGES AND NOTICED A 1200 LB SPLIT. I SAID SOMETHING TO THE CAPT AND HE STARTED CHKING ALL GAUGES; AND PULLED OUT THE CHKLIST FOR SUSPECTED FUEL LEAK. WE DECIDED TO RETURN TO ZZZ AS THE RATE OF DECREASE ON THE #1 TANK WAS UNUSUALLY HIGH. TRIMMED ACFT AND ENGAGED AUTOPLT -- IT DID NOT FEEL THAT UNUSUAL. WE THOUGHT IT MIGHT BE A GAUGE PROB; AS THE FLT ATTENDANTS DID NOT NOTICE ANYTHING VISUAL THAT WAS ABNORMAL AND ALL ENG GAUGES WERE NORMAL. CAPT BRIEFED THAT IF FUEL CONTINUED TO GO DOWN AND GOT BELOW A SET AMOUNT ON #1 THAT WE WOULD SHUT DOWN ENG #1. FUEL AT TOUCHDOWN WAS APPROX 2000 LBS L; 4800 LBS R. LNDG WAS NORMAL. WE WERE MET BY EMER VEHICLES WHO INSPECTED US AND OBSERVED NO LEAKS. THEY FOLLOWED US TO THE GATE; STILL NO LEAKS SEEN. WHEN WE PARKED MAINT DRIPPED TANKS AND FOUND FUEL GAUGES TO BE ACCURATE. CALLBACK CONVERSATION WITH RPTR ON ACN 744288 REVEALED THE FOLLOWING INFO: THE RPTR HAS NOT HEARD ANYTHING FROM MAINT BUT BELIEVES THAT THE XFEED VALVE WAS THE MOST LIKELY CULPRIT.