Definition
A condition in which the oil tank or sump of an aircraft engine lubrication system contains its maximum specified quantity of oil, as marked on the dipstick or sight gauge by the manufacturer.
Plain English
The engine's oil tank is filled all the way up to the highest mark the manufacturer says is allowed.
Context Anchor
Seen in aircraft maintenance, servicing, and weight records where the amount of oil onboard affects the aircraft’s recorded weight.
Derivation
Reservoir comes from a French word meaning “to reserve” or “to store.” That fits the aviation use: the reservoir is the place where oil is stored until the engine or system needs it.
Why Pilots Care
Overfilling past the full mark can cause oil to be blown overboard through the breather, foul the engine, and leave streaks down the cowling. Knowing what 'full' actually means on a given aircraft prevents wasted oil and unnecessary cleanup.
Intuition Check
Do not read “full” as a casual guess that the oil looks topped off. Here it means filled to the aircraft’s specified full capacity for that reservoir.
Example Sentence 1
After the oil change, the technician confirmed a full reservoir of oil before closing the cowling.
Example Sentence 2
A full reservoir of oil prevents lubrication issues during long flights.