LGT HAS FUEL ICING LIGHT ACTIVATE AT CRUISE. APPLY FUEL HEAT CONTINUE.

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UPON ARR AT ACFT IN SFO; ACFT HAD 40000 LBS OF FUEL. WE UPLIFTED THE FUEL TO 46000 LBS USING OUR NORMAL CONTRACT FUELER. HE ADDED 3000 LBS OF FUEL TO TANKS 1 AND 3 (WINGS). APPROX 1.5 TO 2 HRS INTO THE FLT TO CVG FROM SFO LEVEL AT FL330 THE #1 ICING LIGHT ILLUMINATED. THE TAT WAS APPROX MINUS 25 DEGS AND THE FUEL TEMP AT THE TIME WAS MINUS 14. FUEL HEAT WAS APPLIED TO ALL 3 ENGS AND THE ICING LIGHT EXTINGUISHED. DURING THE NEXT 30 MINS THE ICING LIGHT CONTINUED TO ILLUMINATE IN DECREASING INTERVALS WHEN THE FUEL HEAT WAS TURNED OFF. DURING THE COURSE OF THE REPEATED APPLICATIONS OF FUEL HEAT FOR 1 MIN WE ATTEMPTED TO FIND A REF IN THE ACFT OPERATING MANUAL REGARDING THE USE OF FUEL HEAT AND ANY OTHER SUGGESTIONS. NO REFERENCE WAS FOUND OTHER THAN THE TEXT DESCRIPTION OF APPLICATION OF FUEL HEAT IN THE EVENT OF THE ICE CRYSTALS FORMING (NO ALTERNATE OPERATION EXISTS). THE INTERVAL BTWN TURNING ON AND TURNING OFF THE FUEL HEAT HAD DECREASED NOW TO APPROX 3 TO 5 MINS. AT THIS TIME WE ESTABLISHED A PHONE PATCH THROUGH TO MAINT CTL TO ASK THEM IF THEY KNEW OF ANY OTHER REF IN THE MANUAL OR IF THERE WERE ANY RESTRICTIONS TO THE USE OF FUEL HEAT FOR EXTENDED PERIODS OF TIME. THEY INFORMED US THAT THEY DID NOT KNOW OF ANY OTHER REFS; AND THAT THEY KNEW OF NO RESTRICTIONS; THEY ALSO WANTED TO KNOW IF WE WERE AIRBORNE (OBVIOUSLY WE WERE). THEY ADVISED US TO CONTINUE TO CVG. AT THIS POINT WE WERE APPROX 1.5 HOURS OUT OF CVG; I ELECTED TO DSND TO A LOWER ALT AND INCREASE THE SPD SOMEWHAT TO TRY TO WARM THE FUEL TANKS UP. BY DSNDING TO FL290 AND INCREASING THE SPD WE WERE ABLE TO RAISE THE FUEL TEMP TO MINUS 6 TO 8 DEGS. AT THIS TIME THE SO APPLIED FUEL HEAT AT 10 MIN INTERVALS EVEN THOUGH THE ICING LIGHT WAS NOT ILLUMINATING PRIOR TO APPLICATION. THE MECH INFORMED US THAT HE INTENDED TO DRAIN THE FUEL FILTERS AND THE WING SUMP DRAINS PRIOR TO FUELING THE ACFT TO INSPECT FOR WATER. WITH THIS IN MIND; THE OTHER DISCREPANCIES THAT HAD BEEN WRITTEN UP ON THE FLT AND THE DISCUSSIONS THAT WE HAD HAD WITH MAINT CTL AND THE MECH WE DID NOT MAKE A LOG BOOK ENTRY CONCERNING THE FUEL. MY DECISION TO NOT MAKE THE LOG BOOK ENTRY WAS POOR JUDGEMENT ON MY PART; BUT MAINT DID NOT SEEM AT ALL CONCERNED (MAINT CTL OR THE MECH AT THE ACFT) ABOUT THE FACT THAT FUEL HEAT WAS USED IN THIS SIT OR ABOUT HAVING IT WRITTEN UP. I CAN ONLY SAY NEXT TIME IT WILL BE ENTERED INTO THE LOG BOOK. A CONTRIBUTING FACTOR TO MY DECISION TO CONTINUE ON TO CVG AND ALSO NOT MAKE THE APPROPRIATE LOG BOOK ENTRIES WAS FATIGUE. THE HOTEL ROOM I WAS ASSIGNED IN SFO DURING THE DAY WAS ON THE SECOND FLOOR OF THE HOTEL DIRECTLY ABOVE THE RESTAURANT. THE NOISE FROM DOWNSTAIRS WOKE ME AFTER ABOUT 3 HRS. FUEL WAS SUBSEQUENTLY FOUND CONTAMINATED WITH WATER; APPROX 15 TO 20 GALLONS WERE DRAINED INITIALLY. THE ACFT WAS COMPLETELY DEFUELED; SVCED AND SOON TO BE RETURNED TO SVC (IT HAS BEEN 4 DAYS). NO APPARENT LOSS OF THRUST OR ENG INDICATIONS ABNORMALITIES EXISTED AT THE TIME.