Fuel tank return line

Alexander · Post by **Alexander** » Mon May 20, 2002 5:09 am

Where did you guys tap the gas tank for the return line? Did you weld into place or did you get an AN fitting for it? What can you use to seal it?

I am thinking of having the return line come from the bottom of the tank or from the side in the upper half. I also want to use an AN bung/fitting for it but need something to seal it properly (o-ring).

Thanks for the advice,
Alex

Steve Arndt · Post by **Steve Arndt** » Mon May 20, 2002 7:27 am

In my baja I used a 76 beetle tank (since it is a 76 baja!). They have a built in surge ring in the tank and a large 7mm(?) feed and return (the size larger than early beetles).

The return line dumps right into the surge ring area inside the tank.

You are probably wishing that you hadn't sold me the nice swell pot (surge tank) now!

Since you are probably using an original split window gas tank you will need some input from others here.

Steve

Post by **Tom Notch** » Mon May 20, 2002 8:03 am

What year tank?

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Tom Notch
Tom's Old VW Home

Alexander · Post by **Alexander** » Mon May 20, 2002 4:17 pm

Tom,

the tank is my original 52 tank.

Ray,

are you telling me that I do not have to have the return line going into the tank directly if I use a Y fitting right below the tank outlet? One outlet would go into the surge tank and the other would be the return?

Steve,

yeah....I know.....
I am having my friend in Germany building me one now.

Alex

Post by **Tom Notch** » Mon May 20, 2002 5:11 pm

I'm going to graft late model stuff into the bottom of my '51, a surge tank is too heavy

. And if ya think hacking on a '51 tank is bad, I better not tell ya what I'm doing to the deck lid........

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Tom Notch
Tom's Old VW Home

Alexander · Post by **Alexander** » Mon May 20, 2002 7:09 pm

Tom,

welding in vert grills and cutting the decklid open behind the license plate? Already done that, LOL.

I am getting a surge tank already.
But that still does not really answermy question:

Do I need the return line with a surge tank and if yes where is the best location for it?
Does it matter where?

ray greenwood · Post by **ray greenwood** » Mon May 20, 2002 11:43 pm

Alexander, the return line usually either goes to the "R" fitting on the pump...or to a "Y" connector coming from the tank feed to the fuel filter. Ray

Steve C · Post by **Steve C** » Tue May 21, 2002 5:17 am

Hi

I have a surge tank mounted on the chassis opposite where the the master cylinder would be. My return line from the motor and the surge tank both go into the filler neck. I use a Carter lift pump to supply the surge tank. I feel this setup gives the fuel a chance to settle down before getting used again.

Steve C

ray greenwood · Post by **ray greenwood** » Tue May 21, 2002 9:57 am

Hello...don't mess with the surge tank. Its rarely necessary for any application other than say...top fuel. The delivered fuel volume you are dealing with under 3.0 liters in any injection system...is pitifully small. The whole point is to not have a drop in pressure when the injector(s) open...of any sort. What most people fail to realize...is that roller pumps and vane pumps are designed to apply a given rate of head pressure with a given volume. That volume of replacement is not huge. If you have 25 feet of fuel line...lets say each foot holds a volume of 5 oz at X-psi. Then you have 125 oz volume + say...8 oz in a spring diaphram fuel accumulator./ All of this above the pump. The four injectors can rapidly drop that X psi of pressure. The pump...or whatever surge system you have...has to compensate instantly...or you lose power. The larger the surge tank on this pump system, the higher the volume that needs to be brought back to pressure. The pressure way moves slower...the pump lags...the pump life is shorter...you get flat spots. Multiple guages in the fuel loop tell the tale. I actually use a single CIS type diaphram fuel acumulator with lowered spring pressure to match my system. A left and right split for the fuel loop with two equidistant stock pumps...both rails plumbed to a "Y" before a single stock fuel pressure regulator and a single return line...keep pressure stable within less than 1/2 PSI at almost any pressure. Its simple...and makes a difference. I have no idea what a surge ring is in the gas tank...but if its that bubble shaped indention at the bottom of the tank in later models...don't worry about it. It is there simply to keep the sock filter cleaner, allow the tank to run down further, and primarily to prevent cavitation on electric fuel pumps when the tank is low. An easier way to accomplish this is to add an extra filter between the tank and the stock filter. Kind of an accumulator like D-jet has to damp surges. Just a muffin shape can with off axis spigots at each end. Ray

Post by **Tom Notch** » Tue May 21, 2002 5:39 pm

http://home.att.net/~airdoc/notchfi.html

This is the "guts" of a FI T1 and T3 fuel tank. Just a bit more than a dimple in the bottom of the tank. This is what VW put in there tanks to keep the fuel pump pumping in corners with a low volume of fuel on board.

This is what I run in two cars and have no problem with fuel starvation or lean out. One car has a pump out of a 911, the other out of a 944. And its the simpliest fuel system I could devise.

The stock parts work really well, I just used a slightly larger fuel line from the tank to the filter.

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Tom Notch
Tom's Old VW Home

Steve C · Post by **Steve C** » Wed May 22, 2002 5:48 am

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ray greenwood:
The larger the surge tank on this pump system, the higher the volume that needs to be brought back to pressure.<HR></BLOCKQUOTE>

Hi Ray

My Surge tank is in the low pressure area, the Carter lift pump suppiles low pressure but high volume. The EFI pump is after the surge tank so it acts just like your suggestion of using extra filters.

Steve C

Alexander · Post by **Alexander** » Wed May 22, 2002 10:16 am

Steve C,

that is exactly what I have in mind.
They have a nice plan on the SDS website.
I will put the return line at the top side part of the tank. Nice flat surface which should seal better.

Alex

Steve C · Post by **Steve C** » Thu May 23, 2002 3:42 am

Hi Alexander

I used the filler neck on late Beetle as its removable so it can be saftly cleaned prio to welding.

Steve C

ray greenwood · Post by **ray greenwood** » Fri May 24, 2002 5:44 am

Steve, thanks for the clarification. So actually...it is less of a surge tank and more of a volume accumulator to keep the pump from starving? Thats a good idea. Using a tank to keep the pump from starving is a better way to go than re-welding a tank to create the dimple. Since the pumps on all of the VW stock injection were outside the tank, the only part that ever caused starvation was the long sock filter. That should be removed. It caused more pump failures in the middle of nowhere than any other part. When you remove the sock filter, cut about 3 inches off the length of the feed tube. That then puts the tube down in the last 1/2" of the tank. That will negate starvation problems from fuel sloshing. Sediment without the sock filter? No problem...thats what you have an external filter for anyway. I would rather have the filter load up on me in the middle of no where and have to replace it with a spare...than have to drain the gas tank...remove the bung...and clean the sock filter to get going again. Ray

Pillow · Post by **Pillow** » Fri May 24, 2002 7:13 am

I agree Ray that sock filter in the tank is a PITA.

Ray is also on the money with the CIS fuel accuulator to make a steady pressure stream into the fuel distributor/rails. A valuable component I am sure many people probably do not use. Granted I have no idea how Ray changed the spring pressure?

The one very interesting thing I have read about the reason for a fuel return line to the tank is to cool off the gas. Just cooling off the gas, very interesting to me at least. If cooling of the gas was not a factor then you could "Y"/"T" it or loop it right back to the fuel pump and not have to move all that fuel back to the tank. This is where I respectfully disagree with Ray from the information I have read. Now there were no details given on the temperature of fuel returned to the system, so the actual impact on the FI system with "hot" fuel could be minimal to non-existant.

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Adrian Pillow
'66 VW Westfalia - "Biscuit"
'67 VW Deluxe Westfakia - "Dino"
'79 Porsche 911 SC - "Cochese"