When is oil prevented from draining into the sumps?

The scenario where oil is prevented from draining into the sumps occurs when the engine is shut down. During engine operation, oil circulation is actively managed by the lubrication system, which ensures that oil is continuously distributed to various components requiring lubrication. However, once the engine is turned off, certain mechanisms, such as relief valves and check valves, come into play to isolate the oil from the sumps. This helps maintain an optimal oil level for when the engine is restarted, and it prevents contamination and excess drainage.

In contrast, while the engine is running, oil is actively pumped throughout the system, and its flow is directed appropriately, making it unlikely for oil to remain pooled in the sumps. Under pressure, oil is also directed through filters and passages to lubricate the necessary components, while low oil levels would trigger alarms or systems to prevent the engine from running until levels are restored, which does not inherently prevent oil from draining into the sumps.