Custom fuel tank

[gimpyrobb]

SO I have an M35(deuce) army truck. I'd really like to carry more than the stock 50 gallons of fuel. I don't want to use bed space or put another tank in the spare tire's spot. I've been thinking about the space between the bed rails. They are as wide as the frame rails(24 or 27 inches wide) and about 8-12 ft long. I weld as a hobbyist and don't think I want to attempt something this "important". If I were to try it, is there a set amount of baffels I need in a certain span? To check for leaks before I were to put into service, I just fill with water? What else do I need to know or keep in mind? Thanks for any input.

[denrep]

One basic thing to keep in mind is that if the truck is powered by a multi-fuel Hercules, the original fuel tank holds a 24v electric lift pump which is used to feed the engine.

How about modifying the driver's side step to hold a DOT factory built step-tank, complete with brackets, which could all be pirated from another truck?

Good Luck

[gimpyrobb]

The driver's side step is a tool box. I hate to loose any tool storage, I carry a bunch of tools incase of breakdown. One of my other military vehicles has a primary tank on the driver side and a secondary smaller tank on the pass. side. It has its own 24v transfer pump to re-fill the primary tank. I was thinking of using a similar settup(with inline filter). I have a good idea of how to plumb it, just not too sure about making the tank itself. I also forgot in the original post, what size stock to use. Since this sees lots of road and off-road time, I will probably go one size thicker than needed to protect against puncture.

[denrep]

Originally Posted by gimpyrobb

. . .just not too sure about making the tank itself. I also forgot in the original post, what size stock to use. . ..

Well... Steel or 'luminum?

What kinda welder, and what kinda tin-knockin' tools ya got?

And what kinda pin-hole leak-checker ya got?!?

Weld up a box that holds fuel; seems simple and cheap, right? It's neither, but it can be done.


Good Luck

[DSW]

I'd probably head to a junk yard that specializes in heavy trucks and start looking for some thing you can just bolt on. I'm betting with a little bit of thought and looking at all the different shapes and sizes out there, you can find one that will probably work with out major changes.

If you are thinking about a short, long tank here's something to keep in mind. If the tank is 1/2 full or less and the truck sits on a hill or an angle so the pump is on the high side, the tank can be effectively "empty" as the fuel runs away from the pump. I've had this happen to my buddies Mack with dual tanks when parked sideways on a hill when the fuel was 1/4 full. The fuel drained away from the high side pickup and into the low side tank leaving the truck "empty". I also run into this with my L shaped transfer tank. There is so much volume down low that if the truck sits on a sideways slope to the off side, it can hold 15-20 gal and not reach the pump pickup. Even when the tank is level and empty, pitching the truck down hill and putting the pass side tires on the curb will get me 5-8 more gal out of the empty tank.


If you decide to build one yourself or have it built, the purpose of baffles is to limit fuel motion. Diesel is about 7 lbs to the gal.When you slam on the brakes from 30mph, 50 gal of diesel moving 4 feel then hitting the tank wall is going to beat the cr@p out of it at some point. On the other hand if that fuel tank is divided into 4 one foot compartments with baffles, then the 50 gal now becomes 12 1/2 gal and that only moves 1 foot, greatly lessening the force of impact.

[gimpyrobb]

I am thinking of using steel. I have stick, mig and oxy/act settups, but figure I'd use the 110 mig 3200 Lincoln. I have lots of hammers and some anvils I have made. I just got serious about the tank install and plan on visiting some bone yards to see if something close is available. I wanted to start educating myself on what I'll be doing, so this post was made. I knew I needed baffels, just was unsure about how many, good explaination, thank you. I was unsure of the best way to look for pin holes, thats why I figured I'd fill it with water. I also figured I'd have to be carefull transferring the fuel, so I plan on mounting it with a "pitch". All good points, thank you.

[denrep]

Gimpyrobb- I was thinking, maybe you could find a stock under-floor boat fuel tank, made in a shallow flat shape that would fit between the sub-frame's rails?

When mounting the tank, beware that the deuce is a soft truck. They're not as rigid as you'd expect. When used off road they flex like crazy. Also, the top-mount differentials can travel up a long way, so keep plenty of clearance.

Good Luck

[flatbustedbroke]

you said this would be used on the road then it should also meet DOT standards. This alone means that a step tank or something salvaged from another vehicle would be the cheapest way to go.

[gimpyrobb]

Do you think a DOT compliant tank, if modified, would still be DOT compliant? I have a buddy that thinks he knows where something close is. He said he will get some measurements and let me know. Believe me, I would much rather find what I need, instead of building it, but I have seen alot of trucks, setup alot of different ways, and nothing I've seen meets my "vision". I tend to get an idea and not like to deviate from that vision. I know that sounds narrow minded, but there are reasons to have standards. I really hope none of my posts come off too arrogant or serious cause after all, this is just a hobby truck. Thanks for all the input so far, it has made me think about a few points I have not put much thought into.

[hotrodder]

If you can't find something suitable to use...

There's been several threads discussing the baffling of tanks, at least one went into quite a bit of detail with example pics and drawings posted. Be worth a search of the site for some more ideas.

A properly baffled fuel pick up will trap enough fuel for the engine to run for a few minutes when the tank is low and on uneven ground. several ways to do this, one method is to roll some strip into a spiral and weld it in...



I can sort a pic of one from a tank in progress to better explain if needed

Tanks can be a lot stiffer/stronger with some thought over the parts geometry, bead rolling large flat sections and radiused joints rather than regular outside corners...



Flanged joints are another way...

[farmersamm]

And for my 2 cents

See if you can find a used filler hose and filler neck out of an old pickup or one ton. A nice semi flexable rubber fill hose will make life a lot easier when fitting it all together

[gimpyrobb]

Thanks again for the ideas guys. I guess I should have stated in the OP, this will be an aux tank, not my primary feed to the motor. I will be using the original stock tank to run on and have a fuel transfer pump to switch on and off while on the fly. I got over to a buds house this week and took some measurements. The space under the bed is 7"x34"x up to 11.5ft. I did not realize how short it was. Kinda dissapointed, but will adapt and carry on. We did hoist a rear axle up with a forklift till the bumpstops "bumped" and then proceeded to lift the next axle off the ground. Not once did anything travel up into this space. So, I need to re-structure my thoughts and find a suitable solution. I will report back with updates.

[denrep]

Hey Gimp, Pssst... boat tank

[gimpyrobb]

Sweet, how much?

I did a search on craigslist and might have found a guy just down in Ky with some boat tanks. He is supposed to get back to me to see if anything is close.

[farmersamm]

If it's at all possible, Denrep, and his sidekick, will find you a way to scrounge your way out of a dilemna

(Alfred does the legwork, while the boss sits at home sippin' hot choclate, and tossin' bon bons to the pup)

[tankeedog]

I wouldn't use anything but nonmagnetic stainless for a gas tank.

[gimpyrobb]

Well, I caved this weekend. I found a 120gal tank for $80 brandy new. I'll get some pics shortly. Its almost as wide as the bed of my deuce and takes up MUCH less space than an IBC that I had borrowed. I will be boxing it with tubular steel and making a shelf for smaller items to sit on top of it. I will also include some lifting lugs to remove easy. It has lots of fittings built in and looks like I will be able to add a military fuel pump easily, maybe even a sending unit. This tank is new and built to last, I cannot pick it up by my lonesome.

[kenklingerman]

Originally Posted by tankeedog

I wouldn't use anything but nonmagnetic stainless for a gas tank.

why nonmagnetic??

[brandon mitchell]

Originally Posted by gimpyrobb

SO I have an M35(deuce) army truck. I'd really like to carry more than the stock 50 gallons of fuel. I don't want to use bed space or put another fuel tank in the spare tire's spot. I've been thinking about the space between the bed rails. They are as wide as the frame rails(24 or 27 inches wide) and about 8-12 ft long. I weld as a hobbyist and don't think I want to attempt something this "important". If I were to try it, is there a set amount of baffels I need in a certain span? To check for leaks before I were to put into service, I just fill with water? What else do I need to know or keep in mind? Thanks for any input.

Why do you want to have an extra fuel tank on your army truck? Isn't it dangerous to place it on the spare tires area?

[gimpyrobb]

The plan was never to replace the spare. I don't see any danger putting it there though, as the stock tank is opposite the spare's location. The tank I got will be mounted inside the bed when I use it. Why would anyone want an extra 120 gal of fuel? Because I can! I have cheap fuel available to me and would rather not pay $3.00+ per gal when I pay $1.00 or less.

[nk14zp]

It still might leak on its side.

[gimpyrobb]

Originally Posted by nk14zp

It still might leak on its side.

HAHA! I was wondering if you would say anything. The stock tank didn't leak, dunno why this one would.

To let you guys in on the "joke", I might have turned my deuce onto its side in one of my off-road outings.

[ASE_MasterTech]

Originally Posted by gimpyrobb

Do you think a DOT compliant tank, if modified, would still be DOT compliant?

Nope...

[gimpyrobb]

Originally Posted by ASE_MasterTech

Nope...

Yep, that statement was kinda a joke, but thanks for playing. I bought a tank, so no worries now.

[4x4_Welder]

Originally Posted by tankeedog

I wouldn't use anything but nonmagnetic stainless for a gas tank.

Stainless and diesel fuel do not play well together. Actually, stainless as a fuel storage tank material doesn't work well, it corrodes in the seams, leaks, and if left unchecked can split open.
Semi tanks are made of aluminum typically, some get a stainless wrapper to make them pretty.
One thing to keep in mind is that if the tank is used to fill another tank, it must be placarded and you may need an endorsement to carry that amount of fuel. If the engine draws from the tank, it's all well and good.