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RE: [T3] As the Tank Turns - this weekend's episode

> -------- Original Message --------
> Subject: RE: [T3] As the Tank Turns - this weekend's episode
> From: Jim Adney <jadney@vwtype3.org>
> Date: Tue, May 09, 2006 1:31 pm
> I agree. It's confusing here because both the medium and small ports are part
> of a venting system, but I think the small ports only got introduced when the
> overflow tank & charcoal system got introduced

This is plausable.  My 70 does not have an overflow tank or charcoal
tank though.  It/they might have been removed, I haven't made it a
point to look for the canister.  The hose from the vent on the left
side of the tank went down the wiring hole under the brake fluid
reserve and stopped.  that's it.

The 71 tank had the same setup, so this may have been the common "fix"
to a suspected failing charcoal system?

> I'm sure that there's still enough clearance for gravity flow, but with the FI
> systems, the return flow drags along extra gas so that the central cup will get
> filled to a level higher than the rest of the tank. You can actually observe
> this when you start up the car with a low tank. You may have noticed that a
> block or 2 later the gas tank doesn't look nearly as empty as when you first
> started up. This is because the center cup, where the gauge is, is now more
> full than it was when you first started the engine.

Wow...  this reinforces that the VW gas guage reading is questionable at
best.  ;)  :D

> This "jet pump" action is the result of how the return gas passes thru the main
> tank and then enters the cup carrying a little extra gas along with it.

Well, we'll have to see how it goes. I only have one properly aligned
tank that works and i need two, so for now the other one will have to

> Drilling might help or might make it worse. Is the return port straight? I was
> thinking it had a bend in it, or was that only the supply line?

All return ports that I have seen thus far have been straight and
vertical.  The larger supply port is straight, but the petcock (is that
the right term?) that screws on to the supply port and holds the screen
has a bend in the tube (that bend degree varies from what I've seen).

On the Drilling, it can't make it much worse.  The return is 75% blocked
from the factory, (no, the tube is not knocked crooked - I checked) so
drilling it can only help, but will it be enough?  We'll have to see. 


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