[T3] Update with a Bowl Full of Rust Flakes

SCS Crewcab scscrewcab at bellsouth.net
Sun Jul 24 11:30:08 PDT 2011

I just can't picture what you're talking about. I think I understand one 
end of the passageway running under the cup opens into the void of tank. 
Where does the other end open? Into the return tube, into the cup, where 
specifically? Also is there a diagram or a discussion on the function of 
the passageway in the literature?

I'm new here so, maybe I just don't understand how the tank works in 
general. The tank I have has an opening at the very bottom (lowest 
point)  of the tank.  To this opening there is a nut with a fuel line 
that connects to the suction line of the pump. This is the opening that 
has the copper fuel sock filter. There is separate opening at the bottom 
of the cup that connects, via a tee, to the return side of pump. This 
connection does not have any filter at all.  Due to the law of gravity, 
all the gas in the tank (except the small amount remaining in the cup) 
would have to empty through that opening. Is this not correct? If the 
description is correct, what keeps 3/8 of the gas in the tank from 
flowing through that opening when the hidden passageway becomes clogged?

On 7/24/2011 8:38 AM, Jim Adney wrote:
> On 23 Jul 2011 at 22:15, SCS Crewcab wrote:
>> Boy, this sounds ** really ** complicated!  When I look into that cup
>> from the opening for the fuel sender, I see a direct opening to the
>> return line going out of the tank. Looking from the bottom up through
>> that return line, I don't see any openings in the the line other than
>> the one that opens directly into the cup.  Do I have some kind of
>> aftermarket tank?
> Sounds like the standard tank, you just can't see that detail from
> above or below. If there were no other opening, it's pretty clear
> that this would run "out of gas" once the tank dropped to something
> below about half a tank.
> If you watch in the tank with the engine running and the tank quite
> low, you can see that the cup will be full, and actually spilling
> over, while the level outside the tank is well below that in the cup.
> You can also see a high area above the return port, from the momentum
> of the returning gas.
> There's no easy way that I know of to actually see the passages that
> are involved, but you can see the effects of the system on the gas
> level. It's interesting, for example, to watch what happens when you
> start the engine, or just start the pump, with the tank level low.
> You can watch the cup fill up and then overflow.
> Somewhere over the years I've seen a published sketch from VW that
> shows this scheme, and Dave Hall has a sketch of his own on his web
> site that shows how it works. Dave usually steps in and gives us the
> link to that page whenever this topic comes up.

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