Rusty Petrol Tank.

[Spelli]

The next part of my project is to get the rust out of the petrol tank.

I have been using a rust eater product from Frost Auto Restorations. It seemed to be working at first but it seems to be loosing its effectiveness. 
I put a gallon of the stuff in the tank and turned the tank over every day. It has worked quite well but I am struggling to  remove the rust from the raised central section. ( more liquid needed to keep it wet. )

rather than buy more of the product I am eyeing up a gallon can of brick cleaner that is sat doing nothing in my garage. 
I have run a test on some rusty old bolts in a container with a 50/50 mix of acid and water. Looks to be doing the job well. But I am a but worried about putting  it in the tank and splashing it on the paintwork. 
 

Anyone got any advice? Is the a good idea or a terrible one? 
Is there a better way?

[rodneya]

If you use something like concrete remover that is quiet aggressive you will need to line the tank to stop flash rusting.

I used electrolysis for my tank and the last few rounds I used TSP solution. This leaves a phosphate coating that does not flash rust.

[Swiss Toni]

Brick cleaner is a mild form of Phosphoric Acid. That’ll do fine at the dilution you’re using. When you’re done, neutralise the acid with Baking Soda and water.  The surface you’re left with will form a coating against rusting. 

Edited November 29, 2021 by Swiss Toni

[Spelli]

8 hours ago, rodneya said:

If you use something like concrete remover that is quiet aggressive you will need to line the tank to stop flash rusting.

I used electrolysis for my tank and the last few rounds I used TSP solution. This leaves a phosphate coating that does not flash rust.

Thanks for your input. I taken a look at the electrolysis process ( YouTube again)  looks like it might be less risky to the paintwork.

Edited November 29, 2021 by Spelli

[Spelli]

6 hours ago, Swiss Toni said:

Brick cleaner is a mild form of Phosphoric Acid. That’ll do fine at the dilution you’re using. When you’re done, neutralise the acid with Baking Soda and water.  The surface you’re left with will form a coating against rusting. 

Thanks for your valuable input. I did know that the baking soda neutralised the acid so it is important to clean the tank out afterwards with it but 
I wasn't aware the baking soda formed a protective coating against flash rust. 
that is very interesting.
 

I have bought a POR tank sealer   to finish the process which comes with a product called Metal Prep that is suppose to remove rust and provide a final etch for the POR to key to. 
I am not confident that it will remove anything but surface ( flash rust ) so my plan was to use this as the final step before applying the paint. 

I would just like to see as much clean metal as possible before using the MetaL Prep. 
 

Anyone else used this product?

[Swiss Toni]

It’s not Baking Soda that stops the re-formation of rust … it’s the acid. 

Edited November 29, 2021 by Swiss Toni

[bluedog59]

Dezza appears to have got a handle on dealing with rusty tanks, did a couple for me and they came up a treat. Could be worth dropping him a message.

[Muddy]

Tank liners polarise people - some love 'em, others hate 'em.  I've used Red-Kote and KBS both with good results - both are similar to POR from what I understand.  The liner I pulled out of my Kat tank after buying it was just a real mess.  The tank had not been cleaned properly before applying the liner and the liner was just left as a big thick puddle in the bottom of the tank - no wonder it had let go in so many places.  If you spill the liner on a painted tank, it will take a bit of removal.

I do like Swiss Toni's suggestion for a painted tank.

[Swiss Toni]

An alternative (paint safe). Dissolve 1tin of Black Treacle in 1gallon of boiling water. Obviously you’ll want more, but that’s the mix ratio. Fill your tank up with it. Agitate now and again. It takes longer than acid, but won’t damage your paint. Flush thoroughly, and dry. 

[Dezza]

This topic crops up regularly so probably just requires a sticky somewhere. Acid removes rust but only some acids produce some sort of protective coat that does not rust again very quickly unless care is taken. Phosphoric acid and oxalic acid are both used in commercial rust removers. Oxalic is cheap and easy to obtain in powder form. Mix your own solution. I have used oxalic and citirc acid to de-rust tanks with good results. I have also used reverse electrolysis with good results.

Seal the tank using whatever you can find in the shed. The last one I used a bit of old plastic cut to seal the fuel tap and fuel guage outlets with a bit of wilko's finest silicone sealant. Keep the stock cap on. Quarter fill  with the acid solution along with a load of non-stainless nuts and bolts, bits of chain and so on. Close the cap and shake it all about on and off for a couple of hours. Remove the bolts etc. with an extendable magnet, drain, and fill with the solution and leave for a few hours. Periodically open the filler cap to release gasses. Then drain and flush with a garden hose. Then spend a whole load of time drying the inside with a hair drier and dry, dry dry. Keep the tank indoors for a few days to ensure it's completely dry. Then, line with POR (great stuff) or similar or spray a load of WD40, GT85 to prevent further rusting. The acid will not bugger the paint if rinsed quickly with water after contamination.

I have heard that Alan Milliard fills rusty tanks with dilute molasses, leaves for a few days, then flushes and this works well. I have not used this method but he knows what he is doing.

Edited November 29, 2021 by Dezza

[Spelli]

Thanks Dezza, & Swiss Toni

it seems like there are a lot of different ways to achieve the same thing. 

I have always fancy’s giving Molasses a try but have heard conflicting opinions on its effectiveness. But at least it is not going to be as potentially  harmful to the paint. 

If it is good enough for Allen Millyard then it is good enough  for me  

 

I found this video which seemed to speak well of the molasses if a little slow. 
I am not in any rush, so I might give this a try first. 

Edited November 30, 2021 by Spelli

[tobar]

didnt someone on here say DEOX C was great and can be flushed down the drain after?

[rodneya]

If there is a lot of rust or old fuel residue it will speed the process up if you remove some of it first. I put a handful of drywall screws in the tank and sloshed it around with some water. They did a great job scraping off the big stuff and are easy to get out with a little magnet on a telescoping rod or something.

[Swiss Toni]

13 hours ago, tobar said:

didnt someone on here say DEOX C was great and can be flushed down the drain after?

The price of that stuff, you strain it and re-use it!

[Spelli]

So I have decided to go down the Molasses route.

Having taken a look at my trial  using brick acid, while it has certainly removed the rust but I did not like the look at what it had done to the rusty bolt. 
don’t fancy doing that to my tank. 
 

I am not in any rush. So it is the long slow method for me. I will update in 3 weeks or so. Most of the rust has been removed already so it might not take quite as long.

It will give me some time to sort the brakes out next.