I believe most was removed from the MEK due to the thick layer of varnish/guard left in the collection can. As to the Oxi Clean, I use the power washer when raising that out after letting it sit over night. I didn't get a good look before I power washed. I did flush out the tank several times after the Oxi Clean and was pretty brown at first, could be Rust or could be more curd.Nice job so far. Looks like you got all that gooey crud out. Could you tell how much the gunk was removed by the MEK vs the Oxiclean, or vice versa?
Some of those rust spots appear to be a bit deep (difficult to tell in photos). No leaks? If not then check again after the acid treatment.
Phosphoric acid is a relatively weak acid (especially at that dilution) so it's action is slow. I think I let mine soak for several hours and still had to do it again. But I did not use another cleaning agent before the acid (as you did), so that would have slowed mine down. However don't be afraid to let it soak for a couple hours. The acid solution can be reused multiple times. Therefore if it still needs more cleaning then just pour it back in.
After the acid you'll need to rinse it. As much as I hate to introduce water to a freshly exposed metal surface, it is the easiest way with a large tank like this. You can flush it with a garden hose for a few minutes. Then make up a solution of water and baking soda for the final rinse. Do all of your flushing consecutively and immediately follow it with some denatured alcohol to absorb any remaining water. If you don't have denatured alcohol then try using a leaf blower to evaporate the water quickly. It will hide in the seams and crevices so dry it well. While the phosphate film that results from the phosphoric acid will act as a protectant, it isn't perfect. It results from the reaction of the acid and existing rust. Therefore areas that had no rust won't get the phosphate reaction and rust is always a possibility.
That's what I was trying to say earlier about getting it completely dry immediately after the rinse. It's difficult to do.Was hoping the surface rust would not come back so quickly
That grey color is the phosphate that results from the conversion process. Ideally the inside will be that greyish color over most of it, but it will never be 100% [see the note at the bottom of the post about this*]. As Dan says, if you did not get a good change in color then it may need more acid treatment.Since the acid is supposed to convert the bare metal and rust to a phosphate, the only conclusion that can be drawn from the last pic is that wherever the rust is that darker color, that conversion did not happen. Maybe this is telling us that the areas that are still dark-rusty did not get cleaned well enough to allow full contact of the acid with the metal. If that sounds reasonable, maybe another round of degreasing to really get it clean and then another round of acid (or a commercial product like Metal Prep) is called for.
So it sounds like you did get a decent conversion and should not need further acid treatment. As for the flash rust.....When I first empted the tank of the acid, it was gray and white with no rust.
That's what I've been saying, it is critical to get it completely dry immediately. One way to help achieve that is use of a highly hygroscopic agent such as acetone or denatured alcohol. Most tank coating treatment kits include that as the final step prior to applying the actual coating product. It is difficult to properly dry the inside of a large enclosure like the fuel tank.Flash rusted pretty quickly before I got it completely dry.
I don't think you need a sealer in your case. They are better suited to more severe rust conditions where the metal has developed pin holes or very thin/weak areas. The sealant then acts as...well...a sealant.do I use a Tank sealant or just fill it with gas
Just for the record, Metal Prep is phosphoric acid.then another round of acid (or a commercial product like Metal Prep)
Thanks for the insight into your experience, it does seem to be a hit or miss which I'm sure is related to the condition of the tank and its preparation.I did my tank back in 2007. A full report is on my webpage for the car.
No problems since then.