[T3] Blue Coil/Gas Tank

[Jim Adney]

On 29 Jan 2011 at 20:55, Gary Forsmo wrote:

> What I learned (from Jim A.) was that the brass screen filter is mounted to
> the outlet of the tank & sits upright, inside a small, metal "cup-like"
> device attached to the bottom of the tank.  The "cup" and screen are readily
> visible when the sender module is removed.  The "cup" holds a small amount
> of fuel ... maybe 8 to 12 ounces? ... 

That cup is bigger than that. It probably holds at least a half 
gallon.  

> BUT somewhere at the bottom of the "cup", where it goes from the bottom
> to the side, there's a small hole. The function of that hole,
> apparently, it's to let fuel INTO the cup and subsequently the brass
> filter and the fuel pump, etc.  That way when the fuel level in the
> tank gets too low to fill the "cup", fuel can still get 
> through the hole.  

There's much more than that going on. The small hole in the cup is 
right above the return line from the engine. Returning fuel from the 
pressure regulator comes thru that hole and drags additional fuel 
from the tank into that cup. It works like a "jet pump" as used in 
water wells. So this cup will stay full even when the tank is close 
to empty. I think Dave Hall has a sketch of this on his web site.

Unfortunately it will suck in sediment just as readily as gas. The 
only way to keep dirt out of the fuel to that cup is to keep it out 
of the gas tank. That's one reason why it's important to keep the 
overflow hose in good repair.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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