FAA Powerplant Written Practice Test

What is a potential result of not draining the engine manifold lines after shutdown?

1. Engine overheating

2. Fuel boiling and deposits in the lines

3. Increased fuel consumption

4. Air leaks in the system

The correct answer is: Fuel boiling and deposits in the lines

Not draining the engine manifold lines after shutdown can lead to fuel boiling and the formation of deposits in those lines. When an engine is shut down, residual heat can remain in the manifold area. This heat can cause any remaining fuel in the lines to reach high temperatures, resulting in the fuel boiling. The boiling fuel generates vapor, which can create pressure and disrupt the fuel delivery system when the engine is restarted. Additionally, as the fuel boils and evaporates, it can leave behind residues and deposits in the manifold lines, which can negatively affect engine performance, lead to clogging, and impede the proper flow of fuel during subsequent operations. Proper draining of manifold lines helps prevent these issues and contributes to the overall longevity and reliability of the engine.