Vent Line From Trunk to front of engine?

[GGR]

Hi all,

My car is a '71 280SL. I have this black plastic line that runs alongside the fuel and brake lines. It goes from the black plastic fuel tank venting box which is inside the trunk on the left, to the front of the engine, above the crankshaft pulley.

What is the function of this line? What is it connected to in the engine? How does that work?

Thank you very much in advace for the help.

[Tomnistuff]

First let me say that I don`t know for sure.  If I had to guess, based on the fact that your car is a late model, I would say it functions as a fuel vapor cannister purge line (depending on where it is hooked to the engine - probably the throttle body or intake manifold or the crankcase to be sucked into the ventilation system?)  The tank, when filled or when it gets hot, would vent vapors to the cannister where they would be typically absorbed by carbon.  The engine, when it`s running, sucks air through the cannister by way of the plastic line to purge the fuel vapors from the cannister and suck them into the engine where they are burned, thus keeping the atmosphere cleaner than with nothing at all - but not much with 1971 emissions control technology.

My 67 Italian model just vented the vapors to a cannister (probably empty with baffles) where they were either sucked back into the tank when it cooled or as it emptied, or vented to the atmosphere if there was too much vapor to store.

I would be interested to know the real truth about your plastic line, since I`m only guessing (as an ex automotive fuel systems design and development engineer).  1971 is approximately the time frame when we started trying to deal with evaporative emissions from the fuel tank.

Maybe one of the Mercedes (and especially Pagoda) technical experts can elaborate, or tell me I`m completely wrong.

Tom Kizer

[ja17]

You are right, the latest version pagodas had this emission device. The fuel tank vented into the engine crankcase, after passing through the charcoal canister. There is a banjo fitting on the front of the engine block which the plastic vent line attaches to. Any fuel vapors that made it this far, would enter the engine crankcase and would be sucked off through the vent hose on the valve cover and into the intake where they would be harmlessly incinerated by the engine.