B767 flight crew reported loss of oil quantity from the left engine that resulted in a diversion.

Narrative:

While in cruise at FL320; eastbound in oceanic airspace; the left engine oil quantity began dropping. We monitored the loss and contacted dispatch and maintenance control (mc). We continued a dialog with mc as quantity continued to decrease. Oil pressure and temperature remained normal. Eventually oil quantity decreased to zero but pressure remained stable for about an hour. Dispatch and mc were kept in the loop. Oil pressure began to decrease but remained just above redline. Oil pressure yellow caution light began flickering. As long as the engine was still able to operate per QRH guidelines; we considered continuing to [destination]. But weather at destination was at CAT III minimums and forecasted to be that way at our arrival. [An enroute airport] was considered but due to weather and wet and shorter runway and a possible night single engine landing; we decided that our safest course of action was to proceed to ZZZ; which had good weather and long runway. We [advised ATC of emergency] and were cleared direct ZZZ. Engine remained operating and we made a normal landing. Upon investigation; ZZZ maintenance found no oil in the reservoir and oil dripping from the engine and cowling. We secured the aircraft and went to the hotel.

Original NASA ASRS Text

Title: B767 flight crew reported loss of oil quantity from the left engine that resulted in a diversion.

Narrative: While in cruise at FL320; eastbound in oceanic airspace; the left engine oil quantity began dropping. We monitored the loss and contacted Dispatch and Maintenance Control (MC). We continued a dialog with MC as quantity continued to decrease. Oil pressure and temperature remained normal. Eventually oil quantity decreased to zero but pressure remained stable for about an hour. Dispatch and MC were kept in the loop. Oil pressure began to decrease but remained just above redline. Oil pressure yellow caution light began flickering. As long as the engine was still able to operate per QRH guidelines; we considered continuing to [destination]. But Weather at destination was at CAT III minimums and forecasted to be that way at our arrival. [An enroute airport] was considered but due to Weather and wet and shorter runway and a possible night single engine landing; we decided that our safest course of action was to proceed to ZZZ; which had good weather and long runway. We [advised ATC of emergency] and were cleared direct ZZZ. Engine remained operating and we made a normal landing. Upon investigation; ZZZ Maintenance found no oil in the reservoir and oil dripping from the engine and cowling. We secured the aircraft and went to the hotel.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1424856
Time
Date	201702
Place
Locale Reference	ZZZZ.ARTCC
State Reference	FO
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B767 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Engine Oil Seals
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 150 Flight Crew Total 25000 Flight Crew Type 407
Person 2
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Total 2027 Flight Crew Type 558
Events
Anomaly	Aircraft Equipment Problem Less Severe