What is the fundamental difference between a wet-sump and a dry-sump lubrication system on a reciprocating engine?
- AA wet-sump system stores its supply of oil in a sump built into the bottom of the engine, while a dry-sump system stores oil in a separate external tank and uses scavenge pumps to return it
- BA dry-sump system does not require an oil cooler, while a wet-sump system always requires one
- CA wet-sump system is used only on radial engines, while a dry-sump system is used only on horizontally opposed engines
- DA wet-sump system uses grease instead of oil, while a dry-sump system uses liquid oil
Show answer & explanationAnswer & explanation
Correct answer: A. A wet-sump system stores its supply of oil in a sump built into the bottom of the engine, while a dry-sump system stores oil in a separate external tank and uses scavenge pumps to return it
In a wet-sump system the engine's own crankcase sump serves as the oil reservoir. In a dry-sump system the oil is stored externally in a separate tank, and one or more scavenge pumps remove oil from the engine sump and return it to the tank, allowing greater oil capacity and better cooling/aeration control—common on radial and many turbine-powered installations, though the distinction itself is not engine-type specific.
Why the other options are wrong
- B. Either system may or may not include an oil cooler depending on installation.
- C. Wet-sump systems are common on opposed engines, and dry-sump on radials, but this is not an absolute rule and isn't the defining difference.
- D. Both systems use liquid lubricating oil, not grease.
Wet Sump vs Dry Sump
Wet-sump systems store oil in the engine's crankcase; dry-sump systems store oil in an external tank and use scavenge pumps to return oil from the engine.
- Dry sump allows larger oil capacity and separate tank cooling
- Wet sump is simpler with fewer components
- Dry sump requires pressure and scavenge pump stages
Memory trick: Wet sump = oil pool under the engine; dry sump = oil parked in its own tank.