Increasing the capacity

[CRSMP5]

i myself would get 2 disks.. and a sheet to wrap around it.. add a piece of tubing in the middle for support.. so its not a drum.. nipples on 1 side.. rember if you use it to fill the stock tank no baffle needed.. also this eliminates need for gauge, servo/switches and all.. thats how they were designed in 70s... ive seen the kits... read the instructions.. and it was all pre interwebz..

[RabbitJockey]

a local mk1 guy told me that years ago he threw away 4-5 of those spare tanks at the time they were no big deal and he had no use for them. DOH!  theres another fellow around here with an audi 4k tank behind the seat in his mk1 jetta.

[R.O.R-2.0]

The steel 55 will fit in the spare tire well of a bunny..   It's a tight fit, I had to bounce it in there with a mallet..  Nice part about that, no hold down needed...  IIRC I did massage things a bit at the very bottom of the well so that it would fit down down against the bottom, otherwise there was a half inch gap.. I could have made it shorter, but that ran into fitment problems for the goodies in the tank.. I welded a 2" wide ring (like a donut) to the top where I had cut it off, then made a round plate that bolted to that with a gasket so that I could open it up if need be.. The fuel gauge sender (universal type), pickup and return, and a nipple for the filler are mounted in the "lid" as was (for my case) a heat exchanger.. The pickup was just 3/8" brake line welded in there with no screen.. I opted for an inline fuel filter outside of the tank for easier cleaning..

I think when I was all said and done it turned out to be about an 8 gallon tank..  I'd imagine less the heat exchangers it would have been about 8.5 gallon..  A solid lit would work fine for plain ole diesel, since I used it for WVO I wanted the option to be able to get in there and really clean the thing out if need be..

Kevin, baffles are a MUST!!!   I did not put baffles in my tank, and I have darn near paid for it several times taking a turn a bit fast on wet roads.. So far the guard rail and poles have gotten out of my way...

i used to have a big stainless keg in the back of my black bunny, and it looped me out a few times, driving too fast on wet roads with questionable tires..

but!

i had a 15 gallon fuel capacity from the keg..

thank god that toyota pickup got out of my way fast enough!

[ORCoaster]

CRSMP5   Can you expand on this?  . and it was all pre thats how they were designed in 70s... ive seen the kits... read the instructions.

Are you filling the second tank first then having that fill the primary?  Or storing it all and opening some valve to dump entire contents of second tank into primary?  An electric valve? 

I would still want baffles.

My son had that beer barrel setup in his Rabbit for his WVO setup and never complained of the handling.  Maybe because it had tons of other issues and really couldn't race it anyway.  When he cared to go fast it was drive the Miata.

[CRSMP5]

well the spare tire tanks came out late in 70s... in 94ish.. pre interwebz.. somehow i received a caddy, mk1 jetta tank and 2 different steel spare tanks.. all with full instructions.. some stealership in cali found them in the rafters and put a ad in the back of a mag.. and my boss picked them up.. i ended up with mk1 jetta tank.. and he retained the others.. but i did look thru the how to install of them all.. but thats stuff pictured in my brain.. if there was a good relationship with that person scans of his stuff would be tits.. but its sour.. and bitter so not happening..

they would hook  t into the fill pipe between the stock tank and the spare tank.. so filling the car filled both tanks at same time.. and well since main tank is still lower then the sprare tire well it fills up the main tank as level drops.. aka gravity.. they also used a T to hook into the original vent line.. but due to size and both tanks using it.. its a SLOW SLOW fill up.. really need to pull the filler neck and solder a 2nd vent to it..

so yep no baffle needed in the spare tire.. your still getting fuel from stock location.. to feed the engine.. it just fills the main tank via the fill hose..

now for my mk1 jetta tank.. aftermarket people who did the 27gal caddy tanks.. did these (all aluminum/tig welded).. its kinda set up like a audi 4k but again t's into the filler pipe behind the wheel.. gotta be carefull on wheel offsets with this.. to drain it completly it has to also have a t into the fuel return line to main tank.. i can get tons of pics and measurements for this.. i have it in my 84 coupe.. never had diesel in it only gas though.. and that flaw is gas expands in warm/hot weather and to have it full on a 80*+ day makes a hell of a mess as it pshes gas out of anywhere it can.. even with extra expansion tanks i had installed.. no idea how much diesel expands...

the biggest issue i found with it.. when that tank gets 1/2 empty it needs a baffle.. it acts like a unsecured tool box in the trunk.. but spare tire tank is so low its not a issue..

[ORCoaster]

thanks, makes sense in my pea brain.  Not sure what I will do.  Maybe a 5 galloner with a hose to siphon out as the level goes down.

[R.O.R-2.0]

how to increase capacity?

upgrade!

mk2s hold more fuel than mk1s.. i dont remember how much more, but they hold more.. like 3-4 gallons more..

mk3s hold even more than an mk2.

and passats hold A WHOLE LOT, like almost 20 gallons.

[ORCoaster]

I sat with a map and my mileage book and figured out that if I was to get 40 miles to the gallon, which seems to be my low end, that I would need 11 gallons to make the full round trip from the cheap Fred Meyer station in Salem.  The cost is generally 20 cents cheaper than anywhere else on the route and with the foodie discount I knock another 10 off of that. 

I am currently packing an extra gallon in the back as it is my mixer for my wax and ATF.  But that may have to go as I am not going to have the drips all over the new carpet I am trying to install.  I have been dumping that in at the rest area just before the station stop, about 40 miles.  Still rolling in there and getting 10.6 gallons is not a good measure of safety now is it.  So here is what I am trying at this time.

I bought an extra 5 gallon tank that I fill at the station and then remove from the car.  But, I add the one gallon that I use between Salem and Portland back in as I park it for the week.  That way I have enough to get down to home and back to Salem (400 miles) without the need for pouring in the extra.  I still run it pretty low but IF I were to get slowed down in bad weather or got less than 40 mpg then I would pour it in as needed.

This method allows me to get more discounted fuel, keeps me from modifying anything and I can keep the car I have.  Simple solution for now.

DAS

[745 turbogreasel]

My Caddy came with a 30 gal belly tank, and needed air springs if it was full.

[R.O.R-2.0]

My Caddy came with a 30 gal belly tank, and needed air springs if it was full.

HOLY SH**!!!

thats ~250# of fuel and tank when full..

[CRSMP5]

ohhh that nothing..i used to visit myke and pick up bio in my b3 wagon.. fill the main 20 gal tank... then a few 30 gal tall boys... and a few 5 gal cans.. then drive back mostly up hill 4 hours...

when i do my 7k in the toaster ill have a 10-20 gal main tank.. and a 100gal cell inside... 

[BigVWman]

ROR if your making them i'd be in for one preferably fullsize spare mk1 style, i'll figure out where to put the tire later! There is a set of instructions from an old kit scanned in and floating around somewhere i saw last year, maybe vortex if i can find it i'll post it up.
here it is:
http://forums.vwvortex.com/showthread.php?4030569-FS-ACV-Auxiliary-Fuel-Tank-for-the-Spare-Tire-well-Never-installed-with-all-parts