When should a reciprocating engine be pre-oiled?

Pre-oiling a reciprocating engine is a crucial step that ensures proper lubrication of the engine components before the first startup after installation or after a significant period of inactivity. This practice is particularly important for a new engine or one that has been preserved for storage, as it helps to minimize initial wear and tear on the engine during the first operation.

When an engine sits idle for an extended period, the oil can drain away from critical components, leaving them dry at startup. This can lead to increased friction and potential damage before the oil circulates adequately. Therefore, pre-oiling provides a protective layer of oil on engine parts, ensuring that they are lubricated and ready to operate effectively once the engine is started.

Other options may not apply as universally. For instance, pre-oiling only after the first flight does not ensure that engine components are adequately lubricated when they are first used. Pre-oiling before transportation fails to address the risks associated with engine inactivity. Lastly, pre-oiling only after an engine has overheated does not proactively mitigate potential damage from the lack of lubrication. Thus, pre-oiling is best performed prior to starting a new engine or one that has been kept in storage.