Well, it's been a while since I've posted, and of course I still own my AW11s and SW20. After all this time I had to do the FP in my 91 turbo since I purchased it years ago, and well, the tank was rusty.
I did the Muriatic Acid method, and had it soak overnight since the 2-hour max time range wasn't enough for the 1:20 ratio I used for the entire 14 gallons. The next evening, I saw the results and was very satisfied, so, after draining the acid and neutralizing it with large amounts of baking powder, I gave it numerous rinses with soap and water, then soaked it with WD40 spray, where I could get it, and some Marvel Mystery Oil to prevent flash surface rusting. All this actually worked well, and the Acid, despite of the extra time, actually removed all the rust, which appeared more like barnacles stuck on an ocean dock post when I first saw it.
After all that I gave it a few rinses with Acetone, and then spent a few days drying this tank and that was mainly done after I got clever and used my house Dryer to get the job done. Basically, I attached the exhaust hose from the dryer to the Sender unit port on the tank and sealed it all up and let the hot air get it dry. The only thing to worry about on that method is getting lint inside the tank so, it's always good to clean the lint filter before doing such a thing.
So, after this detailed process which became a success, I am now at the stage of using POR15 sealer, to make sure this doesn't happen again, and from the way it looks so nice right now inside, I know that rust will come back with a vengeance, and this is the last hope for this tank to last through the years to come. I did also buy spray rust preventers, but it would be difficult to find a way to extend the aerosol nozzle in such a way as to get all the surfaces inside the tank. This means I will have to use this very expensive, like 70 dollars for a quart expensive, POR15, and use the tank roll method to do so.
Thing is, what about the plastic fuel carrier at the FP port, and then the back flow preventer at the filler port? I worry that this expensive filler will clog up the back flow preventer door flap, and just as well, have some negative effect with the plastic that will be difficult to get around using the rolling method. I also want to make sure I coat the top of the tank on the inside, as there was plenty of rust there too, and so I will have to turn the tank upside down to do so, and that may require hours of rolling just to make sure I get an even coat.
Anyone ever use this POR15 stuff, and if so, how did you coat the inside of the tank with it, and how did you prevent any puddling from happening while doing it? I know this liner is top notch stuff, and I am not worried about it flaking, however, I think it would be difficult to prevent puddling, and also difficult to keep this filler away from the plastics that are inside the tank. Maybe getting some filler on the plastic basket and back flow preventer isn't such a big deal, but I have never used a filler/sealer before so I don't want to risk 70 bucks trying it just yet.
***Edit Update: Just in case anyone else goes through this process..... I have a few things to mention during this de-rust and cleaning of the tank, in an SW20 MKII, and the same would also apply to any AW11, given that these tanks are close enough to partitioned in the same way. What I am realizing now, as I was prepping to apply finisher, is that I have not finished the whole tank yet, given that I could not garden hose pressure spray, each far end of the fuel tank, that are both divided at some point by a metal partition, between each port hole at the top of the tank. What I did not realize and neglected to do, is remove the two evaporators at the far ends, and the back flow preventer that is attached to the metal inlet hose that attaches to the filling end of the tank. Since I did a full muriatic acid soak, brimming to the top, I was able to loosen the rust on the surface metal, however, since I could not spray water hard at those surfaces, the rust appeared to just re dry and now I will have to do an end to end soaking, and I plan to use either concrete cleaner or CLR for a few hours on each end, then re rinse and wash, and get back to using my dryer to get it ready yet again, for the finisher. I am thinking I may be able to buy some kind of hand spray painter, that will have a flexible extendable nozzle that can spray around each one of these port holes.
The main thing I learned during all this, is that if you treat this fuel tank as x4 separate tank, divided by each partition, you can apply each acid bath dedicated to one partition at a time, and then clean and rinse in the same way. Then with this finisher, I have to apply it in this manner as well and try to get into each port hole and apply the finisher for each one, and ensure I don't end up with puddling, or empty spaces just as well. If I had done the cleaning in this manner, after the full tank acid soak, then I would have been able to get to this last remaining rust at the far end of the tank. Basically, I just neglected to remove the two end evaporator ports, and the filler tube port so I could gain access with my pressure wash garden hose and get it all out like I was able to do very well at the Fuel pump and sender unit ports.