A B737-800 RETURNED TO LAND AFTER ATC AND AN OBSERVANT PILOT REPORTED AN ENG FUEL LEAK. MAINT FOUND RESIDUAL ACFT CLEANING FLUID IN THE ENG COWL.

Narrative

AFTER TAXIING USING THE #2 ENG; APCHING RWY XXR FO STARTED #1 ENG; ALLOWING FOR PROPER WARM UP. AT THE HOLD SHORT LINE OF RWY XXR; AN ACFT BEHIND SAID THAT OUR #1 ENG WAS DRIPPING. WHILE IN POS HOLD ON THE RWY AND WAITING FOR ACFT TO CROSS DOWNFIELD THE FO AND I DISCUSSED THE OTHER ACFT'S OBSERVATION. ALL ENG INSTS APPEARED NORMAL. WE BOTH LOOKED SPECIFICALLY AT FUEL FLOWS; WHICH WERE THE SAME FOR BOTH ENGS. WHEN CLRED FOR TKOF AND PWR WAS ADDED TO TKOF PWR; WE DID NOT HEAR ANY FURTHER COMMENTS FROM THE ACFT BEHIND. ALL ENG INSTS CONTINUED TO APPEAR NORMAL AND FUEL FLOWS WERE THE SAME FOR BOTH ENGS. AS THE ACFT WAS ACCELERATING THROUGH 110 KTS; SOMEONE SAID OVER THE RADIOS 'ACR ABORT; FUEL LEAK.' I MADE THE DECISION TO CONTINUE THE TKOF BECAUSE ALL ACFT INDICATIONS WERE NORMAL AND BECAUSE A HIGH SPD ABORT IS EXTREMELY UNSAFE FOR THE PAX AND FOR THE ACFT. SOON THEREAFTER; TWR ASKED: 'ACR X DID YOU HEAR THAT?' I DID NOT HAVE TIME TO RESPOND BECAUSE WE WERE ACCELERATING APCHING OR PAST V1. AFTER ROTATION AND DURING INITIAL CLB; TWR SAID THAT WE HAD LEFT A TRAIL OF FLUID ON THE RWY AND CLRED US FOR A DOWNWIND TO RWY XY. FO FLEW THE ACFT ON DOWNWIND AT 3000 FT AND WAS TALKING TO TWR. I ADVISED THE FLT ATTENDANTS THAT WE WERE COMING BACK TO LAND; MADE A PA TO THE PAX; SET UP THE APCH; AND COMPLETED THE AFTER TKOF; DSCNT AND APCH CHKLISTS. THE TWR ASKED IF WE WANTED THE EMER EQUIP; AND WE RESPONDED IN THE AFFIRMATIVE AS A PRECAUTION. I REQUESTED THE EQUIP BECAUSE THE ACFT WAS BEING LANDED OVERWT AT ABOUT 159000 LBS AND AS A PRECAUTION IF FUEL SHOULD BE LEAKING AFTER LNDG. FO HAD UNEVENTFUL LNDG. AFTER CLRING THE RWY; I ASKED FO TO SHUT DOWN #1 ENG. THE EMER CREW ARRIVED AND SAID THERE WAS SOME FLUID UNDER THE #1 ENG AND THERE WAS A SMALL AMOUNT OF SMOKE COMING FROM THE TAILPIPE. I TOLD HIM THAT WE HAD JUST SHUT THE ENG DOWN AND NORMALLY THERE WOULD BE SOME RESIDUAL VAPOR; BUT TO LET ME KNOW IF IT CONTINUED OR INCREASED. WHILE WAITING FOR ACR MAINT THE APU WAS STARTED AND #2 ENG WAS SHUTDOWN. AFTER ACR MAINT ARRIVED; THE MECH SAID THAT THERE WERE APPROX A COUPLE OF GALS OF FLUID THAT HAD COLLECTED IN THE BOTTOM OF THE COWLING. HE ASKED THAT THE FIRE SWITCH BE PULLED TO FURTHER ISOLATE THE ENG AND IF I WAS WILLING TO TAXI TO THE RAMP ON #2 ENG. I AGREED TO TAXI BACK. AFTER ARRIVING AT THE GATE; ALL CHKLISTS WERE COMPLETED AND A LOGBOOK ENTRY WAS MADE ABOUT THE OVERWT LNDG AND ABOUT THE FUEL LEAK. THE MECHS STARTED THE ENG AT THE GATE BUT COULD FIND NOTHING WRONG. I SAID THAT I HAD FLOWN THE SAME ACFT THE DAY BEFORE AND THAT THE RETURN CREW HAD A PROB WITH THE APU. THE MECH LOOKED AT THE LOGBOOK AND SAW THAT THE #1 ENG HAD BEEN WASHED. HE IMMEDIATELY SAID THAT THE FUEL IN THE ENG COWL WAS WATER/TURCO CLEANING FLUID. TO BE CERTAIN THAT THERE WAS NOT A PROB WITH THE ENG; THE MECHS WANTED TO GND THE ACFT; DRY OUT THE COWL AND DO A HIGH RPM RUN ON THE ENG. I ASKED THE MECH TO CALL ME AFTER THE RUN TO LET ME KNOW WHAT THEY FOUND. FO AND I PREFLTED ANOTHER AIRPLANE AND COMPLETED THE ROUND TRIP. AFTER RETURNING TO ZZZ I CHKED THE MESSAGE ON MY PHONE. THE MECH SAID THAT THEY HAD NOT FOUND ANY LEAKS AND RETURNED THE ACFT TO SVC.