Gas tank anxiety

[Pepperbilly]

Been trying to clean out my gas tank. So far I have used the pea gravel approach. To the point where after several rounds of gravel tumble and water flushing the rinse water runs clear. I don’t see any evidence of pinholes. Looking inside the tank there (especially on the lower half) there is still a brown crust with small areas of shiny metal exposed. I feel like I should treat further with muriatic acid BUT I am anxious about this. The acid step is aggressive and I don’t want eat holes. I feel I should just proceed with the OSPHO rinse and be done with it. I don’t think I am a fan of any tank inner coatings either. Before I make a mistake I am looking for advice now. You can’t replace these tanks.

Bill

[Hawker]

Greetings,

My advice would be to rinse the tank around with vinegar/acetic acid or correctly named Ethanoic acid.

This will dissolve any iron oxides that remain in the tank and will leave you with a clean and shiny tank. It will not attack the metal of the tank itself unlike stronger acids.

BR,

Rob

[raygreenwood]

STOP!

The sloshing around of gravel and things like chains...will work to loosen up crusty rust but it also "scratches" the surface of the steel. This creates stress lines that are more prone to rusting at the scratch.

Ok...a few things.....

Most commonly available CLEANING acids ...will not actually "hurt" steel...structurally. They can cause hydrogen embrittlement at the surface of the steel but since the gas tank is not a high carbon, high performance ...surface hardened steel....we dont care.

Exceptions are:

Nitric acid which reacts with the iron in the steel to produce iron nitrate. Nitric will dissolve steel.

Sulfuric acid can be used for surface pickling but it also is an oxidizing acid.

The two BEST acids for cleaning the gas tank are Muriatic/Hydrochloric acid and/or phosphoric acid.

The best gas tank cleaning method I have found:

NOTE: this assumes your tank is structurally sound...no pin holes or rust throughs.... and can be sealed up. Even if you need to weld it...clean it like this first.

This also assumes you o not have tar or varnish in the tank. Its worth having it boiled out to get rid of that if you cannot use something like solvent or MEK.

Buy a cheap 23 gallon or larger plastic laundry tub. Biggest one you can find. Buy 2-3 five pound boxes of cheap baking soda at walmart.

!!!!!!! Use goggles, gloves and a respirator with an OVP100 acid/VOC cartridge

This first method assumes you have large flakes of crusty rust.

1. Muriatic acid is ideal for removing the crusty thick rust. It literally dissolves rust down to the bare metal. It WILL remove all rust.

Plug up all of the holes with duct tape. Pour about 1 quart of acid in and slosh it around. Take your time. Let it soak for a while at all angles. Keep it over the tub so any leakage goes in the tub.

Pour the acid out into a container and repeat. DO NOT ADD WATER TO THE ACID!

2. When you are ready to neutralize the spent acid....fill the tub with about 15 gallons of water. Pour the acid into that slowly. Neutralize it with a mixture of baking soda and water mixed into a bucket. Keep adding slowly until it quits fizzing. Then dilute with more water. This can now go down the drain.

You will notice...when looking through the fuel sender hole...that after its very clean...it almost instantly flash rusts on the surface. THIS IS WHAT WE WANT!

3. Get any standard phosphoric acid product like Ospho....that does not have to be diluted. Pour about 16 oz in the tank and slosh around and then let it sit for a while. Make suer every surface is coated.

Pour it out in a container and repeat with fresh Ospho. Once its all coated and wet..... DO NOT RINSE IT.

Let it stand and dry with all ports uncovered for 24 hours.

The phosphoric acid will convert the surface flash rust ...into an inert layer of iron phosphate...that WILL NOT RUST...again once the tank is filled with fuel. There is no need for a sealer.

If its going to be a while until you use the tank....put some WD-40 into the tank to slosh it around and coat every surface. This tank can be put on the shelf and not likely to rust in your lifetime.

Alternately.......


If you do not like or want to deal with Muriatic/hydrochloric acid.....look around for a Phosphoric acid product that NEEDS to be diluted. My favorite used to be Jasco metal prep and prime...but they quit making it.

In its undiluted state....it will dissolve rust just like muriatic acid but is a bit slower...les violent and is not an oxidizing acid.

But.....once you use strong phosphoric acid to dissolve the rust....you need to rinse it well with water...but do not neutralize it. It will then take a day or so to flash rust.

Then....use properly diluted phosphoric acid/oshpo ...to convert the surface to the black iron phosphate for rust protection.

There is a little about this process here:

https://www.thesamba.com/vw/forum/viewtopic.php?t=645335&highlight

Ray

[Pepperbilly]

Ray,

Well, I am done with pea gravel part anyway. Just wondering... if someone wanted to use a sealer could you not prepare the OUTSIDE of the tank and apply a coating say like MasterSeries? Do the reverse I guess.

Bill

[raygreenwood]

[Pepperbilly]

Ray,

I am finished with the first step doing two flushes with muriatic acid. I stopped there... no OSPHO yet. What I am seeng is a very clean and rust free upper tank, the exposed metal looks in fine condition. The bottom say 1/4 of the tank has a brownish crud layer still. Does not look like rust. Where clean metal is exposed thru this layer the metal is pristine. It looks like a layer left behind by the old gas that was still remaining in this 1/4 tank area. Now, where to go from here? The tank has no pin holes or rust thrus.

Bill

[raygreenwood]

[Pepperbilly]

Before I try any more abrasive methods it has been suggested to try diesel. Had some extra diesel so what the heck, i’ll give it a try. Will let you know how that came out.

Bill

[KTPhil]

Also check this thread if you are thinking of cleaning and sealing the tank:
https://www.thesamba.com/vw/forum/viewtopic.php?t=748783

[raygreenwood]

[Pepperbilly]

Hey everyone,

Wanted to let you know how the diesel worked. I love it when a project moves forward! I soaked the tank overnite with diesel. When I emptied the diesel some brown sediment came with it... not much though. The tank was still not as clean as I wanted. I flushed further with some acetone two times. Still not what I wanted. Decided I needed the two muriatic acid steps again. After the muriatic soaks I had complete success! The tank looks brand new inside... no brown stuff anywhere. I proceeded with the OSPHO rinse and I am a happy camper. Will coat the inside with some ATF fluid since it will not be holding any gas for a while.

Bill

[raygreenwood]

[Pepperbilly]

I went ahead and prepared my tank for painting. Used MasterSeries silver. Tank was in nice shape with no holes. I think I’m just gonna leave it in MasterSeries silver and not finish paint it in black. Once it’s in the car you don’t see it. It came out nice!

Bill

[raygreenwood]

Man...I just love that paint. Its not cheap...but worth every penny. That stuff is tough as nails and very good chemistry.

By the way...there is another product I highly recommend. Its not a rust killer like Master series silver....but it is a protective coating for painting CLEAN parts. Its like ceramic when its dry.

If you have ever looked inside of an old steam engine or oil field pump jack or pump jack engine gearbox from way back when...and even now days....you see that the inside of the cast iron gearboxes and cases are painted with an absolutely bulletproof enamel coating that lasts for decades. Oils and solvents wont touch it.
It is especially used in engine castings that have been bead, shot or sand blasted. It fills and seals the pores....encapsulates any debris that is also left and makes oil flow off smoother. Its good to about 385* F constant.

Its usually red....sometimes comes in green. I am looking for some in black. Its called "Glyptal paint". It is an alkyd enamel.

Eastwood carries it or you can buy it from the manufacturer.

https://www.eastwood.com/glyptal-red-brush-on-1-qt.html

It is not cheap...but it is killer. The red is Glyptal 1201.

The black is Glyptal 1209. They say its "similar" to 1201. I hope to find out how similar or different.

https://www.electro-wind.com/glyptal-1209-black-en...n-can.html

Wait...here is the main site.

http://www.glyptal.com/glyptal_products.html

I will have to look at the whole line.


Ray