FAA Powerplant Written Practice Test

What is the main source of heat absorbed by lubricating oil in a reciprocating engine?

1. Exhaust gases

2. Pistons and cylinder walls

3. Fuel combustion

4. Cooling system

The correct answer is: Pistons and cylinder walls

The main source of heat absorbed by lubricating oil in a reciprocating engine is the pistons and cylinder walls. As the engine operates, friction is generated between the moving parts, particularly between the piston rings and the cylinder walls. This friction, along with the heat produced during combustion, raises the temperature of the metal components. The lubricating oil serves to reduce friction and wear, and it also helps to carry away heat from these high-temperature surfaces. As the oil circulates through the engine, it absorbs heat from the pistons and cylinder walls, preventing overheating and ensuring that the engine operates within a safe temperature range. This heat absorption is critical for maintaining the viscosity of the oil and ensuring effective lubrication. While exhaust gases and fuel combustion contribute to the overall heat in the engine, the direct contact with the pistons and cylinder walls is where the oil absorbs the most heat. The cooling system, on the other hand, manages the engine's temperature but does not directly contribute to the heat absorbed by the lubricating oil itself.