An engine has a large buildup of sludge in the crankcase. What would cause this problem?

A large buildup of sludge in the crankcase is typically associated with improper ventilation of the crankcase gases. The Positive Crankcase Ventilation (PCV) system is responsible for removing excess gases and moisture from the crankcase, which helps prevent sludge formation. When the PCV valve is plugged, it cannot properly vent these gases, leading to increased pressure and condensation of moisture within the crankcase. This moisture can mix with engine oil, creating sludge over time.

In the context of this question, a plugged PCV valve directly correlates with the formation of sludge because it disrupts the normal flow of gases and can trap moisture and contaminants, contributing to sludge buildup. This emphasizes the importance of regular maintenance on the PCV system to ensure the engine remains free of such issues.