[TRUKTOR]

I scrubbed mine with 'Purple Power' and a stiff scrub brush, and that got most of it. Then, I went after some paint on it with lacquer thinner and then scrubbed it again. It came back very well. On the backside there were some rust deposits from where it rested against the fender and some from the strap.

I used a 'kitchen grade' rust dissolver and it took care of the rust, after many doses. I soaked paper towels with the potion and let them rest on the rusty patches, keeping the areas wet. I wanted to dissolve the rust away, rather than 'convert it', so I stayed away from the stuff that turns the rust black, ready for paint.

I see that your strap is off already, but for the benefit of others -

A note of caution : I had a heck of a time trying to get the strap unbolted at the front. It was stuck tight, and access to the nuts was tricky. The strap wanted to twist into the tank, and it was a real struggle. Eventually I got it free and cleaned the threads all up.
I painted it, and used plenty of anti-seize , as well as stainless washers and nuts, when I put it back together. It was much more difficult than it should have been.

 

[krietpiel]

Thanks Truktor, let the fun begin !
I also managed to track down some tank strap rubber (35mm) which was not that easy ! Nitrile, so it is oil safe....

 

[TRUKTOR]

This is what I used. I didn’t use any sandpaper, but I did use fine Scotchbrite , and it cleaned up the surface but did not dig into the plastic of the tank.

 

[krietpiel]

Whink not available here, but CLR is, and would not be surprised if it contains similar chemicals....

 

[TRUKTOR]

It'll probably do fine. I have both here, maybe I'll compare the labels.

 

[TRUKTOR]

 

[krietpiel]

Oh wow ! hydrofluoric acid is pretty serious stuff - perhaps that is why it worked
Our version of CLR is alkaline and quite mild - so obviously quite different - Mmmmm

 

[krietpiel]

I must be mistaken about it being alkaline - however, it has that soapy feel which is typical of alkalines. I will stick a litmus test strip into it later...

 

[photobldr]

Oh wow ! hydrofluoric acid is pretty serious stuff - perhaps that is why it worked
Our version of CLR is alkaline and quite mild - so obviously quite different - Mmmmm

Yeah, serious. Hydrofluoric acid is used to etch glass (I have done this, actually), and must be stored in polyethylene containers.

Many years ago, I had a rust stain show up on the white marble veneer of a fireplace I had recently built. Not good for customer relations. My dad, being a high school chem and physics teacher, brought home some oxalic acid. We mixed it into a paste with baking powder, painted it on the stains, and covered with plastic to keep it wet. Worked like a charm, but a very slooow charm.

From Wikipedia:

Applications[edit]
Oxalic acid's main applications include cleaning or bleaching, especially for the removal of rust (iron complexing agent). Its utility in rust removal agents is due to its forming a stable, water-soluble salt with ferric iron, ferrioxalate ion. The cleaning product Zud contains oxalic acid.[51] Oxalic acid is an ingredient in some tooth whitening products. About 25% of produced oxalic acid will be used as a mordant in dyeing processes. It is also used in bleaches, especially for pulpwood, and for rust removal and other cleaning, in baking powder,[15] and as a third reagent in silica analysis instruments.

Lee

 

[krietpiel]

Have used oxalic acid - esp to clean timber decks.
Stuck a test strip into the so-called CLR concentrate and I call it a 6. Not that acidic - but certainly not alkaline - so, I am left wondering.....

 

[TRUKTOR]

OK, I'll stop putting it in my coffee.

It just sharpened it up a bit, although I was wondering why the bottom of the ceramic mug was being eaten away.

 

[krietpiel]

After a good coffee and decent scrub, it came up well enough for me to call it a success.
Happy with the result. Just waiting for the epoxy paint on the strap to cure before it all goes back in and another job done

 

[TRUKTOR]

I didn't really find any good 'Before' photos , but I'm sure I must have them. Here are some 'After' shots.

Looking at the backside, you can see the two rusty patches on the back of the tank, a result of it rubbing on the inner fender. There is a second shot showing some of the rust removed.
I kept working on it, getting it almost down to zero, and when the fender was refinished, I placed a chunk of the thin, super-slippery cutting board (can't really call it a 'Board', it is really a sheet, but that is how they market it...) on the fender to separate the two combatants.

The Washer Fluid tank really came out great - The secret potion was toilet bowl cleaner soaking the inside, some bottle brush scrubbing, and then the same sort of scrubbing that the hydraulic tank got on the outside.

The coolant reservoir on top of the engine, uh, not so much. It was recalcitrant, to say the least. I tried every rust dissolving medicine I could come up with, toilet bowl cleaner with bleach, CLR, and I don't remember what all else. I think that once the rusty color is cooked into the plastic, it is there for good. It is a little surprising, as the coolant has always been up to snuff, but looking at many UNIMOG engine bay photos, they are all that way unless a new one has been installed.
So, eventually, I will probably drop the $200 for a new reservoir tank. This is a MB price that is out of line, really. Out of curiosity, I spend a fair amount of time pricing translucent coolant tanks for a wide variety of vehicles, many of which were larger and more complex than the UNIMOG version. The UNIMOG is the Price King, in the bad way.
I really should check TEKSAN, as they should have it. Tomorrow.

 

[krietpiel]

That looks absolutely fantastic ! Job well done Truktor.
Interesting about the coolant reservoir - had the same experience - nothing I threw at it helped !
Some time ago there was a chap on German Fleabay that was selling them new for pocket money ! He did not ship internationaly and I tried to get someone to act as an intermediatory, but too late ! Not surprisingly, they disappeared in a flash ! Still have a bad feeling about that missed opportunity..... Ah well.......

 

[TRUKTOR]

I explored replacing the coolant tank with something else, just to avoid paying the price...
I found some Moon Equipment tanks that could fit, but they would take a lot of work - welding new bungs and so on, and without a sight glass, you could not see the coolant level at a glance.
It could be done, and would look good, but it would explode the concept of saving money.

 

[TRUKTOR]

Moon Equipment is close to McMaster-Carr, so if I was in the area to pick up stuff from McM-C, I'd always swing by Moon for some goof-off time.

 

[Chas Stricker]

I use the oxalic acid for varroa mites on my bees. Do Not Vaporize it!! You will die....just sayin'
Have a nice day,
Chas

 

[m37charlie]

TRIVIA: Re HF (hydrofluoric acid):
It must be quite dilute in that product. My daughter is an isotope geochemist and used concentrated HF to dissolve ground mineral samples for mass spectrometry.She uses a fume hood, protective gear etc. Remember the scene in season 1 Breaking Bad? Where Aaron poured HF over the corpse of the Mexican narco gang member? And what happened after?
HF is the third strongest acid in existence, exceeded only by fluorantimonic - 6 to 8 orders of magnitude more potent, and most potent helonium, HeH+, found only in interstellar space and maybe nuclear weapon boost gas (that would be 3HeT+) after it’s been sitting for a while. HF deserves immense respect, and MUST be extremely dilute in a household product.
Incidentally, one can order concentrated HF online. To my surprise, one can also order fluorantimonic online in small quantities, very expensive.

 

[TRUKTOR]

The warning label.