ABYC Diesel Practice Exam

If a mechanical engine exhibits oil leaking from the front crankshaft seal, what is a likely cause?

1. Excessive engine wear

2. Plugged crankcase breather

3. Low oil level

4. Faulty oil filter

The correct answer is: Plugged crankcase breather

When a mechanical engine shows signs of oil leaking from the front crankshaft seal, one of the likely causes is a plugged crankcase breather. The crankcase breather is responsible for allowing gases to escape from the crankcase, which helps to equalize pressure within the engine. If this breather is clogged, it can lead to increased pressure inside the crankcase. This excess pressure can force oil past the seals, resulting in noticeable leaks. Understanding the role of the crankcase breather highlights why addressing its condition is essential for maintaining engine integrity. A blockage not only risks oil leaks but can also contribute to other performance issues, such as oil foaming or greater wear on internal engine components due to poor vapor escape. While other factors like excessive engine wear, low oil level, or a faulty oil filter can affect an engine's performance, they don't directly cause oil to leak specifically from the front crankshaft seal in the same way a plugged crankcase breather does. This makes recognizing the symptoms associated with a blocked breather crucial for troubleshooting and maintaining the engine effectively.