Which one is the return line n a w116 300sd?? the one on the top or bottom?

cigar hose to the top .. on a w123.

incoming fuel to the prefilter on the bottom.

unless my setup is wrong - someone correct me.

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yup that's correct, the cigar hose is intended to "soften" the pulses from the lift pump so you don't hear the vibrations as fuel travels back to the tank. As if you could hear it over the engine anyway

so bottom line, cigar hose from big spin on fuel filter is the return.

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http://i106.photobucket.com/albums/m...73378_30-1.jpg

My W210 has a venturi pump in the tank to scavenge low areas into the splash bowl, using the return flow for the power. Does the W123 use such a device? If so, perhaps the softening of the pulses is to help that pump perform properly. But I really am guessing.

no it does not. There is only a screen.

It would be a nice upgrade though. I begin to lose fuel supply well before the end of my tank - and it is clean.

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That was fast. I love this forum!

Glad we could be of help

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http://i106.photobucket.com/albums/m...73378_30-1.jpg

I thought that hose was about to burst because of the shape so I replaced it with a regular piece of hose. Is it there only for that noise issue? If so, I will just leave it the way I have it.

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http://img212.imageshack.us/img212/5...andbenzqj3.jpg1979 W123 300D Silver with Blue interior