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Old May 3rd 2010, 16:05
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Installing a Larger Tank in a Split Bus

by Adrian Pillow
Dec 10, 2003


Have you had trouble in the past coordinating potty breaks and gas stops? Getting sick of stopping at the local "Gas, Beer, & Biscuits" every week? Well here is a simple solution for a late model split window bus driver to increase the stock tank of 10 gallons to a super size 15 gallons!

At the same time I took the liberty of improving the fuel lines to prevent the dreaded fuel cracks and subsequent engine fires. This was mostly inspired from the Novemember Hot VWs magazine technical article which illustrated some tricks for added fuel flow to a Beetle.


Here is a quick list of the supplies needed:
  • Split window gas tank fuel neck
  • Early bay window bus fuel tank (including fuel sender) and rubber fuel hose with clamps
  • POR-15 gas tank sealer
  • 1/4NPT pipe tap
  • (1) Aeroquip 1/4NPT to -4AN 90 degree elbow
  • (1) Aeroquip -4AN straight bulkhead/firewall fitting
  • (2) Aeroquip -4AN bulkhead fitting lock nuts
  • (3+) Aeroquip -4AN to Pushlock hose fittings
  • (7 foot) Aeroquip -4AN Pushlock hose
  • (2) Scrap metal strips 1 inch wide
  • (2) Nuts nylocks and (2) Bolts normal 8mmx1.00 with the bolt 1.5-2 inches long.
  • Scrap hard foam or rubber padding


First step is to aquire a bay window bus (type 2 from 1968-1979) fuel tank, which are all 15 gallons. I took an early bay window bus unit that was used with a carbureted engine as I knew the hoses and connections are easy and would match my current fuel system needs.

I am not familiar with the differences in a later 1975+ bay window tank that ran fuel injection. The next item needed is the old fuel filler neck from the current split window tank. I used a high speed cut-off wheel to chop it off in short order, right around 9 inches is more than enough. See the attached photo to get an idea.

Now is a good time to start mocking up and modifying the parts as they are filthy and in need of help anyway. Cut the split fuel neck to a good length in proportion to the bay tank, this will hook together with large rubber fuel safe hose used for VW fuel necks, allow some good overlap here so the hose gets a nice tight fit.

Take the bay tanks fuel sock and drain pipe out, now throw them away. Get out your trusty 1/4NPT tap and bore out the middle of the old fitting nipple on the tank. MIG Weld or JB Weld (epoxy) the top breather outlet to the tank closed if so equiped. Now on to the cleaner jobs!

Of course when you get a used tank it is probably pretty ratty inside... This called for a trip to my local industrial rust stripper to have the tank acid dipped. In Atlanta a place called "Unpaint Corp" is the only way to go. They dip any fuel tank until it is clean (3-5 days) for a flat fee of $50. This includes the filler neck. Remember to remove the fuel sender before having it acod dipped unless you really wanted to buy a new one

Once you have the clean tank it must be teated quickly as to prevent rust from setting into the clean naked metal. The tank comes back with an oily residue/preservative on it that I removed with Acetone cleaner, clean inside and out thoroughly. I then primed and painted the exterior of the tank, let set for a day.

Now comes the fun part of sealing the inside of the tank! I used POR-15's product for this task which they call plain old "U.S. Standard Fuel Tank Sealer". Just follow the directions on the label and you cannot go wrong. Pretty painless, but has a long curing time so do not be in a rush to put fuel in the tank a day later.

Now re-tap the 1/4NPT drain fitting as the sealer will have junked it up. Same for the fuel sender mounting holes if they got plugged as well. Now is a good time to trial fit the 1/4NPT to -4AN fitting in the hole.

Cring, cring... Get the drill out and put a hole through the bulkhead for the -4AN bulkhead fitting. I believe I used a .5 inch bit and it worked out just fine. Install the fitting and use the two -4AN bulkhead nuts to lock it in tight.

Time to start closing the deal! Reinstall the fuel tank sender onto the fuel tank. Mock up the connecting wires and lengthen as necessary to meet your busses wiring needs as the bay tank cannot use the stock split wiring as it is too short. Install the bay tank!

You will notice there is play in the tank as it does not fit securely on the tank mounting surface, this is where some scrap foam padding or rubber padding will work great to reduce play and secure the tank from movement. Attach the rubber fuel inlet hose and fuel filler neck, simple in theory but can be a little difficult as access room is tight to fit them on.

Snug up the two tank stamps and it is done... Oh wait a minute they are too short! Here is the only challenge in the whole conversion, making some extensions for the gas tank straps. Take some scrap metal 1 inch wide strips and mock them up to the tank to see the length you need.

Bend some 90 degrees in them and drill for 8mm bolts on the top and bottom. Re-use the lower 8mm bolts as before and use long 8mm bolts/nuts for the top connections. Allow long bolts to really get some clamping action on the tank so it will not move at all. Not that difficult of a task but time consuming for sure.

Install the lower tank 90 degree 1/4NPT -4AN fitting since the tank is in its final resting place and secure. Measure the hose length from the bulkhead fitting to the tank bottom fitting, cut the Aeroquip Pushlock -4An hose to fit. Install the AN Pushlock fittings as instructed, pretty easy. Attach to the bulkhead and tank fitting, use the stock fuel line metal tab clamps to hold the hose in place.

Measure the hose distance from the bulkhead fitting to the fuel pump (in-line fuel filter if desired) and cut to length. Install the fittings and run the hose as to avoid hot areas that would compromise the hoses longevity. Depending on the fuel pump style will depend on what connection is needed at the pump.

I chose the Aeroquip Pushlock system as it is very easy to use and yet carries a very high pressure rating with the largest ID (inner diameter) of all the Aeroquip hose systems. The -4AN hoses in Pushlock carry a .25 inch ID which is right on track for most VWs needs. For the all out HP fanatic go for the -6 setup though or anything with fuel injection.
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bus, gas tank, type 2

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