FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationHard
A mechanic is inspecting a reciprocating engine equipped with an oil dilution system used for cold-weather starting. How does this system function?
- AIt circulates hot engine coolant through the oil sump to maintain oil temperature
- BIt injects unleaded gasoline directly into the intake manifold to aid cold starts
- CIt heats the oil sump electrically to keep oil warm between flights
- DIt introduces raw fuel into the engine oil supply just before shutdown to thin the oil, which evaporates out after the next start warms the engine
Show answer & explanationAnswer & explanation
Correct answer: D. It introduces raw fuel into the engine oil supply just before shutdown to thin the oil, which evaporates out after the next start warms the engine
An oil dilution system introduces raw gasoline into the engine oil supply just before engine shutdown in cold weather. This thins the oil, making it easier to circulate for the next cold start. As the engine warms up after starting, the gasoline evaporates out of the oil, restoring normal viscosity.
Why the other options are wrong
- A. Coolant-based oil heating is not part of an oil dilution system; reciprocating engines are typically air-cooled.
- B. Oil dilution modifies the oil itself, not intake manifold fuel injection.
- C. Electric sump heating is a separate preheat method (oil sump heater), not oil dilution.
Oil Dilution System
A cold-weather starting aid that mixes raw fuel into engine oil before shutdown to reduce viscosity for easier starting; the fuel evaporates from the oil after the engine warms up.
- Fuel is introduced into oil supply just before shutdown
- Thinned oil circulates more easily during cold starts
- Gasoline evaporates from oil as engine warms after starting
Memory trick: Dilution thins the oil like adding water to syrup for easy pouring in the cold