so currently I have a thread in the sale section where im trying to unload an overstock supply of fuel tanks ive been storing for an alt fuel company. I have about 30 of the things I need to sell to make room for a mezzanine and staircase, and im selling them without all the bits that make a alt fuel system, so this thread is basically a how to on using these plastic tanks as just a big 18gal extra fuel tank for anyone who has purchased one of them off me.

Im selling them without mounting hardware, fuel pickup ect, so im hoping anyone who has bought one will chime in with their solutions and ideas on installation.

so here is the item-



underneath there is a pretty decent fuel sump-



the features are pretty nice, the ones I have are unfinished tanks, so there is a big bolt pattern that hasn't been cut out

this pic shows the top features-



Its got fill spouts on either side, and the boss at the lower left of the pic above is for the rollover vent.

Biggest issues with using this tank are going to be figuring out mounting I think. I will be installing one in my 83 240 and documenting what I need to do to plumb and bolt the thing in.

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Would this fit in the trunk behind the regular MB fuel tank? What are the external dimensions of this thing?

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Unfortunately I'm on my phone and can't save a hyperlink, but the external dimensions are in the parts for sale thread I have. I believe its 12 inches deep, by 30 something long, but definitely double check down there
Its designed to fit against the back of the trunk up against the regular fuel tank, at least that's how it fits in my 123, the design seems to be a universal general trunk mount setup

EDIT- dimensions on the large one are- 12 inches deep, 36 inches long, and 14 inches high

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so I had purchased one of these things a while ago with all the parts, so ive got some stuff to reverse engineer against for those of you who have one.

This is approximately where it would sit in the trunk of a 123, and where I will mount this one below-



Here is the same tank mounted in my old car when I had bought the whole shebang a while back and fully installed it. basically this thread is going to be about reverse engineering a lot of the bits that come on this tank that i dont have. Most of the accessories on here we have to come up with-




This is the mounting hardware that would come with a full $700 dollar alt fuel product. Its pretty clever the way they have it set up, they are using several sections of C-channel steel for the tank to sit on, and steel straps that go over the ends



The lowest point of the fuel tank is actually this sump, so it has to sit up on something on the ends, it won't sit flat. its 1/2 inch lower than the rest-



the strap channels are 1.5 inches wide-



Here is some C-channel steel I have laying around that I bought at fastenall. This works perfectly as a pair of rails for the tank to sit on. When I first bought the above tank for my old brown 240, I used two pieces of this C-channel to mount it instead of the weldable pieces they sent me. The usual purpose for this stuff is hanging lighting and drop ceilings and whatnot. Fastenal carries an incredible selection of hardware that can fit in this style C channel. I believe this is the type of hardware the manufacturer is using also

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Thank you for the pics.

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no problem!


ok, more info. For this part of preparing the tank, you definitely could use a dremel tool or similar and a drill.

Below details installing the roll over tank vent. The purpose of this vent is if you happen to roll your car, the vent will seal closed and prevent the contents of the fuel tank from dumping out and possibly igniting in an accident situation.

What I have sent with each tank is vents I got from the manufacturer, they are kelch brand, and consist of the vent itself, and a bushing.

This is what it looks like on the finished tank they sent me. I assume you can point it in any direction, but they pointed it at this angle if you want to duplicate-



what you get with the tank-



The unfinished boss on the tank itself-



First thing you want to do is drill a hole down the center of the boss. (note, metal tools will cut through the plastic like butter, this whole process does not take too long, but be careful not to cut too much too fast)



Then widen the hole with your dremel tool, the object is to get it to a nice sliding fit for the bushing, you don't want it too loose-
This will also create a lot of debris



The hole will look approximately like this, and the bushing should pop in like so-




next lubricate the sealing surface of the vent (otherwise its impossible to install), and press it into the bushing, it should pop into place, and be able to rotate. The pressure of the vent on the bushing will make an excellent seal around the hole.
EDIT- Note, I just tried turning the vent in the tank I bought a couple years ago, and the vent body itself looks like it might break before it actually turns, so before the lubricant dries up and the rubber bushing gets a solid purchase on the plastic, better to decide what direction you want it to face when you can turn it.




and you are done, apart from vacuuming up all the debris.

Also, while you have your dremel out, check your fill ports for width compared to the cap. I noticed that on the one I bought from the manufacturer, that they had cut back around the inside of the fill a little to match the sealing groove on the cap itself-



here is what the unfinished one looks like, the cap cranks down with a satisfying click, but it won't truly be sealed, it will be a hard plastic to hard plastic connection. You need to cut back a little to make sure the threaded part actually seals down on the rubber gasket

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Ok, this post is about making the tank straps.

For this you will need-

1- a piece of 2 inch pipe, or something that is 2 inches around and hard enough to bend things against
2- A vice
3- A hammer or mallet
4- drill
5- Masking tape

So step one is visit home depot of maybe lowes. All the parts to build the mounting bracketry just like the manufacturer are available in either the electrical section of the home depot, and in the hardware section. (I assume lowes also)

The electrical section has the C channel and C channel specific spring nuts you want to grab. hardware has steel stock for the straps

Here is an example of the C channel spring nut-



I purchased 2 1/8th inch thick, 1.5 inch wide, flat bar stock 4 feet long. Don't get anything shorter than 4 feet, thats just the right length with a little extra. Also, I would get 3 bars, one as a practice piece.

parts from home depot-



Next grab you masking tape and tape it to the tank like so, and mark the bottom, and the centerpoints of the corner radius on the top-



Remove and place the masking tape on the bar stock like so, and transfer-



(note, the following pics show a 3 inch pipe being used, the radius on the tank is pretty close to 3 inches, so I tried that first, the problem is when you bend it back to 90 degrees, you end up with much closer to a 4 inch bend instead. The principle is the same, but use 2 inch pipe instead of what I used in the pic.

Here is an example of how close to the right bend 2 inch pipe will give you!
Its pretty much perfect



take your bar stock and mount up like so. I used a clamp to make sure my radius center point didn't move



then bend both curves-



next go in to where you marked the bottom, and make a 90 degree bend



you end up with a piece that looks like this. Factory below, jury rigged above-



Even my test piece with the wrong radius makes a pretty fair tank strap-



Once you have two of these made, grab your C channel spring nuts and break off the springs, (or keep them if you went with the far thicker C channel). You will have to break the spring off it you want to use the C nut in the factory depth C channel though.

The nut will slide like so in the C channel-



last step is cut the ends off the straps where you want them, drill 4 holes to accept bolts to run into the C channel spring nut. The factory tabs area about 1 and 3/4 inches long with a hole in the center for the bolt

Cut two pieces of the C channel 16 inches long (same as the factory pieces I have), and you should have your mounting system!

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ok, some pics on the top plate these tanks are designed to use.

The unfinished tanks have a solid plastic top with a hole in the middle-



By design these are supposed to be removed. The structure is very solid, so you could just drill holes in this for your fuel sender and pickup, but if you want to remake the plate designed for this tank, here are some steps and pics-

this is a factory plate- (painted as ive been making templates for everyone who bought one of these)



Here is how it fits in the top of the tank- it actually has three ports by design, one comes down right in the center of the sump, the other one is outside the sump, and they had a capped third center threaded hole which is for an optional return for the alt fuel design with heat exchanger.



The stock plate is 1/4 inch thick aluminum. To meet design specs, im told that we should use either 1/4 inch plate minimum if we use aluminum, or 1/8th thick steel plate. Ive chosen to make my new plate out of 1/8th steel. The 1/4 is nice because you can tap right into it, but im going to be using bulkhead fittings for my 2nd aux trunk tank, so I went thinner-



every tank ive mailed out comes with this paper template I made of the stock plate I have in hand-



The idea is cut this out, and tape it to your top material you have chosen-



Then go around and centerpunch all the bolt flange holes, including the centerpoints for the fuel pickup and sender if you are installing one-



when you are done, all you need to do is cut it out, and drill the holes, ill update this when I get my plate all ready

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cutting out the top of the tank-

So I consider this definitely worth doing, as there is quite a bit of debris that ends up down in there from doing the vent-

First I drilled a bunch of holes in the corners-




then I used one of these blind end hack saws to cut it out-



definitely worth cutting out, as this is the debris that ends up in the tank from the vent cutting-



I went around and sanded a bit to get rid of burrs that might fall off and get sucked up eventually-



looking down into the freshly cut out hole where you can see the pickup area-

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so a small update. Over the last couple weeks, ive been buying and rejecting valves to switch between stock and aux tanks. Either too complex, or too poor a quality. Ive been doing the same thing with switches off amazon, ive bought a few aux tank switches for ford dual tanks or whatnot, and every time they arrive, the quality is so poor, that I couldn't allow them to be part of this project. The car is currently out of my hands getting rust repair, but soon I should have it back and get the tank installed

How I intend to plumb this is with its own fuel gauge and a switch between the two.

This is the valve I think Im going to use. It seems to be a decent quality, and it has very decent reviews on amazon. its also extremely simple, grounds through the valve body, and 12 volts to the center post. Any switch will do, so I can find something really nice.

Its a GM dual tank application I think, for much older vehicles, I think 60s-70s. The part number is- AC Delco 467513. Another part number on the box is BOO16HT92G

here is what it looks like-

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finally have the car back, and its time to get this thread updated as a few more people have tanks.

This post will deal exclusively with mounting one of these tanks in a 123 chassis sedan. Things will not be identical for other chassis or other applications, but the basic process for setting up the rails should be the same.

First I made a cardboard template of the shape of the bottom of the tank, and I cut two sections of perforated C-channel to 16 inches long.

with the tank upside down, it looks like this-



then I placed the template in my cleared out trunk-



On a 123, it turns out to be really convenient to line up the brackets. The driver side lines up perfectly with the body feature shown here-



and the passenger side lines up perfectly with the edge of the spare tire well-



I removed the tank and marked all the hole positions I could potentially use-

NOTE- super important lesson I made a mistake on, DO NOT bolt the rail down at the very end of the rail. If you do that, you can't get the strap hardware into the rail.

driver side pic, notice the shaded area above shows where any hole will come down into a closed frame member instead of through the floor-



passenger side as well-



Next to really get a clean install, you should drop the exhaust and remove the heat shield. It doesn't have to come down too far, just enough to grab the bolts-




On the passenger side, the holes come right down into a protected area and can be easily accessed. I made mine right next to each other, but I could have spaced it a little more



Once everything is buttoned down, the rails look like this in the trunk-



The hardware slides in the rails like so-



The tank will sit nicely on both rails. Even though the passenger rail is suspended partway over the spare tie well, the tire is easy to remove and install, and it seems nice and strong. I wouldn't using anything other than grade 5 or 8 bolts with lock washers to attach these rails. (I used grade 5).

I have been told that screws should not be used to hold down the rails, remember this thing is going to weigh as much as a person, a screw into sheet metal will have the thing flying around with ease in any accident.



Next step is cutting a hole for fuel supply and return, and getting the plate finished and tank permanently installed

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next step, finishing the tank top. This post will deal with completing the top part of the fuel tank to prepare it to be installed-

Here is my steel top plate cut out, and a hole drilled for fuel sender, and two holes for bulkhead fittings.

NOTE- I did all this with a regular hand drill, hole saw, drill bits, and an angle grinder to cut out the plate. No special tools beyond these basic ones required



Here are the fittings for the plate, I have two brass bulkhead fittings, and I grabbed two huge fender washers and bored them out a little to fit, so I had a large gasket surface.

Im also using an ISSPRO brand fuel sender. looks just like MB stock. Its a 12 inch fuel sender, the model number is RA9512-ISS.
These are available off of egauges .com
link- RA9512-ISS: Fuel Level Senders: Tube Type Senders (240-33 Ohms) - ISSPRO - egauges.com

NOTE- I was unable to find a single piece standpipe in copper or brass or even steel for my chosen pipe thread of 1/4 NPT bulkhead fittings. I didn't check plastic, could be its available. If I had gone up in size to 3/8ths NPT, I could have done the pickup as one piece. In the pics I had to use a union halfway down the pickup. Hopefully should not be an issue as I sealed it pretty well, but still, would be nice as one piece



Everything installed in the painted top plate-

NOTE- I couldnt use the ISSPRO hardware to screw down the fuel sender, as I drilled through holes, instead of tapping. I just swapped for some long machine screws instead.



Moving over to the tank, I bought a roll of 1/4 inch rubber round O-ring cord stock from mcmaster carr a while ago, and made an O-ring (plus some others ive been shipping out). Basically its cut to fit, and superglue together.
McMaster-Carr

However, I realized its really really hard to get the O-ring which wants to be a big circle to sit in the rectangular groove on the tank. The tank I bought several years ago, everything was already assembled, so the O-ring was already kind of a rectangle. I taped it down first, but then used spots of superglue to hold it in place which worked well!



Here is the tank top bolted down and the feed pipes installed. (im using 3/8ths supply hose, and 5/16ths return)

NOTE- before threading in the bolts, (which are 1/4-20 thread pitch), take a pick and clean out the aluminum inserts on the top plate. I noticed some have plastic that got in the threads, but its easy to pick out.



Another NOTE- I used 1/4-20 x 3/4 socket head cap screws that came with the original plate, and they are too long for this steel plate. Using 8th inch steel, it should really be 1/4-20 x 1/2 instead. I spaced mine out with extra washers to make it work, and keep them from bottoming out.



Next on the original tank there was weather stripping on all the strap locations, so i duplicated that top and bottom-

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Valve installation and line routing (123 chassis sedan specific)-

Earlier I had bought a 6 port 12 volt actuated valve off amazon. (part number above). Ive never seen one of these before, and haven't run it yet for any time, so it remains untested, but looks decent enough. Hopefully this upcoming week i can get some testing in.

For hose routing, I decided to go through the enclosed square channel of the body on the passenger side. There was already a large factory hole here-



I drilled two holes above, and installed grommets




Next I fed my supply and return lines through the body and out the stock frame hole (no pic from below, but pics later when I get into plumbing)



For the valve mounting, I decided that sort of protected area on the passenger side right in front of the spare tire well would be a good place. Its reasonably close to the stock lines, and I would be able to build a protective plate fairly easily once the plumbing was finished.

Inside and outside-




More pics of this later when I T into the stock fuel system

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Installing the fuel tank and finishing the trunk area apart from wiring-

Before installing, mark and cut your carpet around the rails, and nip the spare tire cover-





Once thats done, installation is really easy. First, (and I made this mistake) install and tighten down the back side of the tank strap-



Then you can slide the tank in and move the straps over the ends without too much difficulty-



Then you can bolt down the front-



Final step is connect the fuel lines-



And its in, the only thing left in the trunk is wiring up the fuel sender.

NOTE- The fill port looks like it will clear a normal style diesel pump fill under the rear deck, but I need to get pics of this and test it out to be sure.

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Just tested it out, filling is not bad, pop the trunk and fill stock and aux tanks at the same time pretty easily.

One thing I would do different is pull further forward and run the hose in from the back of the trunk to not muss up my new paint. And keep some towels handy on overspill.

I mounted the rails right up against the stock trunk wall, if you were to space them out an inch or 2, filling would be that much easier for a 123. Not bad as it is though. I kept careful watch of the pump to avoid overfilling and getting diesel in the trunk carpet area.

Next step is attaching the aux setup to the stock lines, looking forward to my 450-500 added miles of range on this 240.

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