What is the maximum allowable vacuum drop when the engine is turned off?

The correct answer regarding the maximum allowable vacuum drop when the engine is turned off is two inches in three minutes. This standard is important because it helps ensure the integrity of the vacuum system within the brake system. A vacuum drop greater than this limit may indicate a problem such as a leak in the vacuum source or in the system itself, which can lead to reduced brake performance and potentially compromise safety.

Maintaining a vacuum level is crucial for components that rely on vacuum assistance, such as power brakes. If there is a significant drop in vacuum, it signals the need for inspection and potential repair to prevent brake failure. Monitoring vacuum drop is part of routine maintenance checks, allowing technicians to identify issues early on before they escalate into more significant problems.

The other options reflect a standard that is not considered acceptable, indicating a greater vacuum drop which may suggest more severe issues with the vacuum system or components. Hence, two inches in three minutes serves as a benchmark for acceptable performance in vacuum systems used in brake applications.