In what scenario would engine overhauling be considered necessary?

Engine overhauling is a comprehensive process that is necessary when an engine has experienced a significant mechanical failure. This situation often requires extensive inspections, repairs, replacements of components, and thorough testing to restore the engine's performance and ensure safety and reliability. The process involves disassembling the engine, examining all parts for wear and damage, and addressing any issues that may lead to decreased efficiency or potential failure during operation.

A mechanical failure typically indicates that critical components have either failed or are failing, which necessitates a complete overhaul to prevent further damage and to bring the engine back to a serviceable condition. This proactive approach not only ensures peak performance but also extends the engine's lifespan and maintains compliance with safety regulations.

The other scenarios provided do not warrant an overhaul, as routine maintenance such as oil changes does not typically require extensive disassembly or repairs, and replacing certain components without a major failure may only necessitate targeted maintenance rather than a complete overhaul.