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Discussion Starter · #1 ·
Took my tank off today in readiness for an outer repaint and inner surface treatment.
After I took the cap housing off, the pump, filter, etc, out I noticed the inner surface is coated in a metallic gold substance. So I'm wondering if it's paint, some type of metal treatment, or the original colour. There was some on the rubber fuel hoses so I'm betting it's sprayed or painted on after factory. Any thoughts?
The surface appears to be in good condition though, with no visible rust.

The front floor of the tank, shallow end, has surface rust so will use Metal Rescue Rust Bath on there, but as for the gold coating I'm thinking I should allow sleeping dogs to lie.

Cheers.
 

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If the coating is not coming off I agree with you, leave well enough alone. It would be nice to know what it is , though.
 

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I'm guessing the "gold" color is fuel residue. I would not coat the tank unless you have a significant rust problem.
 

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Discussion Starter · #4 ·
I'm guessing the "gold" color is fuel residue....
I dunno, as I stated in OP there appears to be overspray/paint marks on parts of the rubber fuel line (& elec. wires). Also the two brackets that hold the fuel pump are coated with the mystery 'metallic gold' but the pop rivet heads attaching the bracket are not.

Probably one of mysteries that will never have a unanimous answer.

Cheers.
 

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Discussion Starter · #5 ·
The mysterious substance (closer to bronze) is a tank liner of some sort. Anyway it had come away from the inside top and front surfaces, which allowed a fairly gruesome layer of rust to form.

From what others reported I decided on using Oxalic Acid. Twelve hours overnight and shiny new.
It is as good as reported; easy to use, cheap, safe for paint, rubber, plastics, everything except rust.
I don't have a before pic. but one can imagine it, rust is rust.

Cheers.
 

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Did the acid remove the coating as well?

This has been the worst part of re-coating tanks when they come in with a failing coating it can be a nightmare to remove all the old coating. I do like the idea of NOT coating as long as you can get away from it. One of my concerns with a acid washed tank will be flash rusting of the now bare metal. Keep a close eye on the top side of the tank where you often have no fuel to see if it flash rusts or is kept lubed and a layer of fuel keeps it rust free.
 

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Discussion Starter · #7 ·
Did the acid remove the coating as well?
It' still intact; the magic quality of Oxalic is it only affects rust. Re flash rust, it doesn't (at least not for awhile) - I can't explain why although someone has in a forum here already.

The painter found some repaired pinholes at the lower rear corners so that explains why the tank was coated originally. He pressure tested it and all is good.

l will regularly check the top underside for new rust and always top up after a ride.

Cheers.
 

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In your second pic it looks like a hole in the metal line ?
 

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Okay so it converts/removes rust but does not harm coating, our fuel in the states would be trying to get under the coating and lifting it so without a full membrane of a coating it would likely fail at some point. I may try the Oxalic at some point just to test, please do let us know how it holds up over time. I assume you do not have ethanol in your fuel with is a large part of our issues in the states, and trust me we have plenty of issues.
 

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Discussion Starter · #11 · (Edited)
Okay so it converts/removes rust but does not harm coating...
Correct, and there are you tube videos of it's use in action.


I assume you do not have ethanol in your fuel.....
Ethanol added fuel is a separate bowser so we have a choice. Older vehicles stay away from it.

Here is an explanation of how oxalic works, from a bike forum:
"Oxalic acid is superior to other acids for rust removal because it forms complexes with iron ions much better. The oxalic acid can pull the oxidized iron out of the rust and into solution where it can be washed away. Anyone who has seen a pale green color in the oxalic acid bath after soaking parts for a while has seen the iron-oxalate complex ([Fe(III)(C_2O_4)_3]^{3+**) in solution. Other chemicals will do this, including acetic and citric acids, but because of its structure oxalic acid is the optimal choice.
Yes, I'm a chemist."

Cheers.
 

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grrss
Thanks for the educated explanation, I am always looking for options as we seem to lose them more than we find new ones. I will order some up and test it out on a couple tanks, Thanks again.
 
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