Definition
An engine that stores its lubricating oil in a separate external tank rather than in a reservoir at the bottom of the engine itself. Oil is pumped from the tank through the engine to lubricate moving parts, then scavenged out of the engine by a separate pump and returned to the external tank.
Plain English
An engine whose oil supply is kept in a tank outside the engine, not pooled inside the engine's lower casing. Oil is pumped in, used, then pumped back out to the outside tank.
Context Anchor
Seen in aircraft engine lubrication discussions, oil servicing procedures, and maintenance descriptions for engines that use a separate oil tank.
Derivation
Sump comes from Middle Low German 'sump,' meaning a pit or pool where liquid collects. In a 'wet-sump' engine, oil pools inside the engine. In a 'dry-sump' engine, that internal pool is kept dry — the oil lives in a separate tank instead.
Why Pilots Care
Provides reliable oil pressure during aerobatic or inverted flight and improves engine cooling.
Intuition Check
Do not read “dry” as “no oil.” A dry-sump engine still uses oil; it just stores most of that oil in a separate tank.
Example Sentence 1
Because the aircraft has a dry-sump engine, the technician checked the oil level at the external oil tank rather than at the engine itself.
Example Sentence 2
Many aerobatic aircraft use a dry-sump engine so the oil supply stays steady when the plane is upside down.