AFTER PERFORMING A FUEL SUMMATION UNIT (FSU) CHANGE AND ADJUSTMENT; TWO MECHANICS WERE INFORMED THAT THE FLIGHT CREW HAD REPORTED THE B737-300 HAD EXPERIENCED AN INCORRECT FUEL LOAD AND A CORRESPONDING LATERAL IMBALANCE.

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ACFT COMPLETED AN OVERNIGHT VISIT. DURING THIS VISIT THE ACFT REQUIRED TROUBLESHOOTING OF THE FUEL SUMMATION SYSTEM DUE TO AN MEL. THE MAINT MANUAL WAS USED TO ADJUST THE SUMMATION UNIT TO MATCH THE TOTAL FUEL OF ALL COCKPIT INDICATORS. HISTORY ON THE ACFT DID NOT REFLECT ANY FUEL QUANTITY PROBLEMS; WITH THE EXCEPTION OF A BAD INDICATOR. DUE TO THIS HISTORY; THE FUEL QUANTITY SYSTEM WAS CONSIDERED GOOD SO THE TEST AND ADJUSTMENT WAS CARRIED ON PER THE MAINT MANUAL. THE TANKS WERE NEVER DRIPPED NOR WAS FUEL ADDED OVERNIGHT TO TROUBLESHOOT THE SYSTEM. TO THE BEST OF MY KNOWLEDGE; ACFT LEFT ON ORIGINATING FLT WITH A FUEL IMBALANCE. IN CLOSING I WOULD LIKE TO RECOMMEND THE MAINT MANUAL AND MEL BE REVISED TO REQUIRE THE TANKS TO BE DRIPPED ANY TIME THE SUMMATION UNIT IS REPLACED OR MEL IS APPLIED.SUPPLEMENTAL INFO FROM ACN 815527: TROUBLESHOOT ACFT FUEL SYSTEM PROBLEM NIGHT BEFORE. COULD NOT DUPLICATE ON GROUND. CHANGED FMC; GAUGES (FUEL); FUEL SUMMATION UNIT; ALL NO HELP. LEAD CHECKED HISTORY OF FUEL SUMMATION SERVICE REPAIRS TO SEE IF WE WERE GETTING BAD PARTS. ADJUSTED FUEL SUMMATION UNIT AND SIGNED OFF. MEL WAS CLEARED. NO FUEL WAS ADDED THAT NIGHT. I FUELED ACFT IN MORNING TO FUEL LOAD. I FOUND OUT CREW HAD INCORRECT FUEL LOAD INFLT AND NOTICED THE ACFT ROLLED TO ONE SIDE SUGGESTING INCORRECT FUEL BALANCE. DECIDED THEY HAD ENOUGH FUEL TO GET TO DESTINATION. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING INFO: REPORTER ACN 815527. REPORTER STATED THE B737-300 DID HAVE A HISTORY OF THE COCKPIT #1 FUEL QUANTITY GAUGE PROBLEMS. THE AIRCRAFT PREVIOUSLY HAD ALL THE COCKPIT GAUGES REPLACED INCLUDING THE LEFT WING TANK FUEL HARNESSES. HE ALSO REPLACED THE FUEL SUMMATION UNIT (FSU); WHICH IS AFT OF THE FIRST OFFICER'S SEAT; AND ADJUSTED THE FSU TO THE COCKPIT GAUGES USING A TEST BOX. REPORTER STATED HE NOW BELIEVES IT WAS AT THAT POINT; AFTER ADJUSTING THE FSU; WHEN THE FUEL QUANTITY DISCREPANCY WOULD HAVE BEEN CAUGHT; IF THEY HAD DONE A FUEL DIPSTICK READING OF ALL FUEL TANKS. BUT NEITHER THE MEL DEFERRAL OF THE FSU; OR SIGNOFF OF THE DEFERRAL; REQUIRED A DIPSTICK VERIFICATION READING. THE MAINTENANCE MANUAL ALSO DID NOT REQUIRE A DIPSTICK CHECK. AND THEY JUST DID NOT THINK OF IT EITHER. AS A RESULT; THE AIRCRAFT LATER EXPERIENCED A ROLL TO ONE SIDE FROM A WING FUEL IMBALANCE. REPORTER STATED A FUEL DIPSTICK READING IS REQUIRED ANYTIME ANY FUEL QUANTITY GAUGE HAS A PROBLEM; OR IS DEFERRED. HIS CARRIER IS NOW CONSIDERING ADDING LANGUAGE TO THEIR MEL; REQUIRING FUEL TANK DIPSTICK READINGS BE ACCOMPLISHED WHENEVER THE FUEL SUMMATION UNIT (FSU) IS REPLACED; ADJUSTED OR DEFERRED. THEIR MAINTENANCE MANUAL IS BEING REVIEWED BY THEIR ENGINEERING GROUP. REPORTER STATED HE DOES NOT KNOW WHAT ACTUALLY FIXED THE RECURRING FUEL INDICATION PROBLEM.