B767ER ENRTE OCEANIC HAD LOSS OF OIL QUANTITY AND PRESSURE INDICATOR WENT INTO RED. FLC DECLARED EMER AND DIVERTED BACK TO DEP ARPT. ENG WAS SHUT DOWN AFTER LNDG.

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APCHING 42N50W WE NOTICED THE L ENG OIL QUANTITY DECREASING. AT 5 QUARTS I CALLED MAINT/FLT CTL ON THE SATCOM AND DISCUSSED THE PROB WITH THEM. IT WAS DECIDED THAT AN IMMEDIATE RETURN TO JFK BE MADE. WE DECLARED AN EMER WITH ATC AND RECEIVED A CLRNC BACK TO NEW YORK. DURING THIS TIME THE ENG OIL QUANTITY GRADUALLY WENT TO ZERO. ABOUT 45 MINS OUT; WE STARTED TO GET SOME FLUCTUATION ON OIL PRESSURE; THEN A GRADUAL DECREASE. AT TOP OF DSCNT (ABOUT 15-20 MINS OUT) I CAME BACK ON THE THROTTLES; AT WHICH TIME WE RECEIVED A LOW PRESSURE LIGHT; EICAS MESSAGE; AND THE OIL PRESSURE INDICATOR TURNED RED WHILE STILL INDICATING 70-90 PSI. THE ENG WAS LEFT IN IDLE FOR THE REMAINDER OF THE FLT WHILE OIL TEMP AND OTHER ENG PARAMETERS WERE CAREFULLY MONITORED. OIL TEMP REMAINED COOL AND AN UNEVENTFUL LNDG WAS MADE ON RWY 31L. THE ENG WAS SHUT DOWN AFTER TURNING OFF THE RWY. THE ENG PROBABLY SHOULD HAVE BEEN SHUT DOWN. HOWEVER; THERE IS CONSIDERABLE PRESSURE TO KEEP THEM RUNNING TO MAINTAIN ETOPS CERTIFICATION. ALSO; OUR POM IS NOT REAL CLR ON WHAT COLLABORATING EVIDENCE IS IF WE GET A LOW OIL PRESSURE INDICATION. IS LOW OIL QUANTITY SUFFICIENT OR SHOULD WE WAIT FOR A RISE IN OIL TEMP. I ALSO HAD THE RWY IS CLOSE SYNDROME AND MY FO'S COUNSELED ME NOT TO SHUT IT DOWN. DID I ERROR? YEAH; I SHOULD HAVE SHUT IT DOWN. BUT; THE WATER LOOKED SO COLD.