I tried searching for the line "Sailing off to..." but no luck.

This is probably not the song you are looking for but it came up on a search using "Finished With Engines" - my trick is to use the double quotes to search for the whole phrase:

Finished With Engines

I can't hear the line "Sailing off to who knows where, and returning who knows when" in it. It is a song about the Titanic.

An explanation of the use of the term Finished With Engines is here:

"It is a maritime tradition that when a member of the engine department passes away he is said to be 'finished with engines'."

Another page about fixing motor cars has a brief explanation:

Finished With Engines or FWE is the final entry in a ships bell log marking the end of maneuvering. it is also traditionally written in the turnover/log by engineers who are departing the vessel.