What does that engine vent/drain hose do?

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After long, high speed trips in my 93 W250, I notice that the engine vent hose drains about a silver-dollar sized amount of fluid (diesel?) onto the ground. What does that thing do and why does it vent?

Any Ideas

 

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That is the crankcase breather hose. It's purpose is to allow the crankcase blow-by pressure to vent to atmosphere. This pressure relief prevents blowing out the crank seals or pan gaskets.
A few drips are considered normal after a hard run.
The fluid in the tube is residual crankcase oil.

[This message has been edited by old school (edited 12-09-2000). ]