Fuel tank removal

💡⚡️❄️DRY ICE!❄️⚡️💡 That would be both cheaper and more effective at shrinking the tank, than gas, you'd need to let it boil off before trying to remove the tank as it might make the tank too brittle, and the weight would make removal more difficult, but hopefully it would go back to it's original dimensions and stay there due to it's plastic memory.

The use of a plastic tank would've been motivated by the same old reason we have to suffer the fall out of stupid decisions.....Cost!  tooling for roto-molding is much cheaper to make and maintain than the stamping dies for pressing  out metal sheet, and all you have to do is pump the required amount of molten plastic from the extruder into the mold and multi axis spin it to use the centrifugal force in combination with gravity and vibration  depending upon the complexity of the shape to make to hollow form you require, where as you need to stamp out the sheet metal and them weld the two halves and any other shaped features such as the filler tube neck and any double skinning required like the gauge/ fuel pump mounting points, brackets etc. to a fuel tight seal!

Does anyone know exactly what the properties of the fuel tank are, i.e what are the materials of construction/which particular plastic.
I definitely would not use dry ice.
When dealing with rubber lined storage tanks the life span was seriously affected if contaminated with traces of organic materials.
So there will definitely be things not to use.
If "the words of wisdom" passed down the food chain by "the elders" is such that time alone leaves the tank marginally smaller then I can only imagine that the use of copious volumes of warm air passing through the tank will aid that process. But if it is too hot it may have a detrimental consequence.
(Pour boiling water into a fizzy drinks bottle and watch what happens ~ it shrinks and becomes far less pliable).

The tank will in all probability be polypropylene, that's the go to plastic if an inert & resilient material is required. We've just replaced the chairs at church & have stripped the metalwork off, the fabric & plastic: the plastic is polyprop & I want to make a form to cast some fibreglass & assumed that by heating the stuff up I could produce what I wanted. I cant get the entire piece to soften uniformly to do what I want. And she came home early when I had it in the oven. The bollocking wasn't as bad as expected.
Right Cobbs. Your problem is only a pain in the arse when its your arse where the pain is, the rest of us are just fine. Mind you there only seems to be you who are troubled. The tank is an odd shape, you knew that when you started & as the car is supposed to be a light weight sports car a metal tank would be counterproductive.
It was made by a cash strapped company, which is why they went for the cheapest, most appropriate material. There is only you who has recent troubles, & that was due to Antipodean Rotten Rust Riddled Rolling Juice, whose to blame for that?
Thuryar yuv bin reet bollocked futhi daftnes. I have another idea, which I'll return to later, Av bin shoutid after. (my wife requires me).
As ever, your friend M

That is indeed a bollocking....of the friendliest kind.... but we all wish Cobber a good result or we will never hear the end of it.

Is there not a way that a flexible magnet would pick up the rust?  Not as dumb as it seems mate.

 

Plastic fuel tanks are made from HDPE, High Density Poly Ethylene,
Often SoarnoL is added.
 

There mixed in with his vast mechanical knowledge is a firm grasp of material science, lost to most folk. And this is no piss take, it is genuine admiration. Would this soften more evenly than PP in my wife's oven?
M

Seriously...a long flexible rod with a magnet attached would hoover up the ferrous flakes.
I've done that myself with an old Celica tank which is harder because it's steel.

I've worked for various plastics manufacturers and recyclers over the years, in fact I've worked in a vast array of manufacturing fields due to being a contractor who's specialty is plant installation and relocation means I move about a lot so always dealing with something new, always learning....the day I stop learning is the day I will have dropped dead!
I can't imagine working in the same place day after day year after year doing pretty well the same thing my whole working life. Even then I've wandered in and out of other fields like highrise construction, telecommunications, ship building, and rail. Still so much yet to learn and have a crack at!

If HDPE then it suggests it is a welded tank construction rather than bonded. From what I can read it will not withstand temperatures approaching 80 degrees C.
It can be prone to cracking.
My suggestion would be the magnetic fishing rod even if you had to put water in the tank and slosh it around a bit to get the rust close to the magnet.
Failing that try dilute HCl and wait for that to dissolve the rust before pumping that out and starting a caustic wash followed by lots of water until pH neutral. Stand back when changing from HCl to NaOH though so I’d give it a good rinse before introducing the NaOH.
Not a simple process.

A magnet on the end of a piece of string works..you can swish it about at will.

The tanks were blow moulded & I think they are polyetherketone (PEK).
Or so I've been lead to believe.
M

This is just a thought, a theory.
In another life I supplied air movers of the type shown, you provide a compressed air supply at around 4 bar at the threaded port shown.
The locking ring allows adjustment of the unit on a large screw thread, the units are assembled in 2 halves, this way you adjust the suction..
It utilises the coanda effect, for every litre of air supplied it pulls 7 litres through its body.
It is essentially an air powered vacuum cleaner, no electrics required, except of course at the compressor.
They come in various diameters, small enough to fit a tube that will go down the fuel filler end of a fuel tank.
So, you can with a piece of flexi tube and a compressor clean out the tanks, safely hopefully.
The bigger the compressor the more suction you get, but an average garage compressor can do the job.
it is best to fit a tube at the exhaust end, otherwise you get petrol soaked crap all over the workshop.