[NylonAdmiral]

I'm thinking about making my own fuel tank. I'd like to make one to fit under the car which will mount as the original stock one did.

I'm trying to work out what the best material is to make it out of and it seems to be hotly debated online. Some people seem to think stainless steel tanks are more likely to crack whereas other seem to think aluminium ones are, but I'm guessing it must somewhat depend on the application and also the skill of the fabricator. Most of the discussion around aluminium vs stainless tanks seems to be for marine applications whereas I'm looking at an automotive application.

I'm guessing there must be a few professionals on this forum with experience of making fuel tanks?

Is there any reason to favour one material over the other?

My current tank looks like one of the ones in this picture:

Original.jpg (7.29 KiB) Viewed 2929 times

The one I'm thinking of making would look something like this:

modified.jpg (7.31 KiB) Viewed 2929 times

I would however strengthen it with beads rolled in to the panels etc.

Thanks for your thoughts

[Otto Nobedder]

Material choice is determined by a few factors you must balance. Cost is one, environment is another. Aluminum is a good choice, but in the installation it must be completely isolated from the steel structure of the car, or there will be cathodic corrosion. A high-salt environment will accelerate the process. This means Buna-n or silicone isolation pads everywhere aluminum would otherwise touch steel, including any bolts in brackets, or straps like the factory uses. This creates both a cost factor for the protective measures and a design issue to allow room for the isolation at every point.

Stainless steel, such as 304 and 316, are NOT immune from salts, but the effects can take more than 20 years to show and tend to happen along welds, and in very small ways that don't present the risk of sudden failure.

So, you have a cost-benefit analysis to do. Both are good options.

Steve S

[LtBadd]

Just curious, why do you want to make a fuel tank for your car? Larger capacity? Perhaps a Mad Max modification?

[NylonAdmiral]

Otto Nobedder, thanks, good points about the isolation. This should be relatively easy as the standard tank uses isolation pads around the top of the tank and rubber between the tank and mounting straps. This will hopefully make the same setup relatively easy to reproduce on a new tank.

LtBadd, for three reasons really. Firstly the tank is pretty tatty, I looked inside it the other day and there's a lot of rust/flaking coating etc in there so it would at the very least need to be blasted and recoated if I were to use it again (I got quoted £300GBP for this which would easily be enough to cover the build costs of a replacement). Secondly, the original engine was carbed and the current engine is fuel injected so it would require modifying anyway. Thirdly, it's a bad design. There are no baffles or anything in it but there is one partition about a third of the way from one side. Oddly the fuel return seems to feed back to the smaller side of the partition, and the pickup seems to draw fuel from just the other side of it. This means if you were going round a right hand corner, the fuel in the larger partition is going to be thrown to the far corner away from the pickup, and the fuel that's being returned is being dropped the wrong side of the partition.

If I make a new tank I can solve the surge problem through better design, alter it to be suitable for fuel injection, and have a nice new tank for the same price as what it would cost me to get it refurbished anyway.

Plus, it would just be a fun thing to make anyway

So in terms of an automotive application, if we ignore the issues of cost and assume that the tank will remain isolated, there isn't any particularly strong reason to use one material over the other? I'd read some people saying that stainless welds can be more brittle than aluminium welds which might make them more susceptible to cracking in a high vibration environment such as an automotive one. Does this sound plausible or is it nonsense?

Thanks for your input both.

[Poland308]

That issue with SS is possible but usually a result of no back purge and running way to hot on the weld. The cracks will show up next to the welds along the edge. If you carefull and don't cut corners it will probably never crack.

[ex framie]

I'll swim against the current here and say why not mild steel? Zinc coated, will provide added protection everwhere except the weld and HAZ.
This is what the after market long range tank builders use here in oz.
For extra protection you could use kreem or por15 tank sealeants.
Why steel?
Cost
Ease of welding
No back purge required
Strength and impact resistance.
Multible choices of welding process.
Minimal cracking issues.

Thats my call.
Goodluck with the project.

[Coldman]

The long range aftermarket tanks available through arb and tjm etc are aluminiumised after fabrication not zinc. I have not seen any zinc coated tanks with untreated welds, who makes them?

[NylonAdmiral]

Well at this stage, I'm not really too fussed about the cost, it's largely a no-expense-spared build and I just want to use whatever will be best for the application rather than be most cost effective.

The other thing with steel is that although the materials are cheaper the subsequent finishing costs of treating/sealing etc all start to balance the total cost out anyway. By the time the tank was finished it would most likely be the heaviest too. In addition to that, most of the contributors on this forum seem to live in the States where many of you benefit from a warmer environment. With the fuel tank sitting where it does, it's in a prime place to corrode away here in the UK! Wet weather and salted roads are a nightmare. Even with the exterior fully coated, if you get any stone chips or scuffs in the exterior then you'll quickly get rust developing underneath. Corrosion resistance was the main reason I wanted aluminium or stainless.

If I used stainless would I need to get the tank passivated once it's finished?

Thanks again for everyone's input.

[ex framie]

The long range aftermarket tanks available through arb and tjm etc are aluminiumised after fabrication not zinc. I have not seen any zinc coated tanks with untreated welds, who makes them?

Seems I stand corrected.
Wasnt aware they aluminised them after the welding, makes sense though.