FAA Powerplant Written Practice Test

During an engine shutdown, why is it important to drain the manifold lines?

1. To prevent fuel boiling and deposits due to residual heat

2. To allow for faster engine restart

3. To reduce engine weight

4. To minimize noise during shutdown

The correct answer is: To prevent fuel boiling and deposits due to residual heat

Draining the manifold lines during engine shutdown is crucial because it helps to prevent fuel boiling and the formation of deposits caused by residual heat. When fuel remains in the manifold lines after the engine has stopped running, the heat from the engine can cause the residual fuel to heat up, potentially leading to vaporization. This can create vapor lock, which makes restarting the engine more difficult and can impair engine performance. Additionally, the accumulation of heated fuel may lead to the formation of deposits inside the manifold, which can negatively affect the fuel distribution to the cylinders the next time the engine is started. By draining the manifold lines, not only are you reducing the chances of these issues, but you are also ensuring that the fuel system remains clean and functional for future engine operations. This practice contributes to overall engine reliability and helps maintain optimum performance.