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So far the only leaks have been at the petcock, fuel level sensor, and the expanding plug I put n the fuel fill hole. This is encouraging news! Tomorrow I will drain all of the Evapo-rust and rinse out the tank. I will then inspect the insides with a bore scope to see how well (or not) the rust has been dealt with. The plan is to mask all openings really well, and bead blast the exterior clean in prep for the paint. All the other bodywork is ready for final paint, so the tank is the hold up. Either the tank is at paint by the end of Thursday, or the restoration work continues next week as I am off to bounce around the desert with a group of friends over the weekend. Still crossing my fingers that no weld repair is required.

Belly of the beast!

I know you are on a path there and I don't want to disrupt it but Home Depot sells some phosphoric acid sauce denoted Kleen Strip Metal Prep. If you strip all the paint on the outside of the tank, remove the sensors and petcock, then sink the tank in a tub with water/metal prep the sauce will clean the metal nicely and leave behind a great surface to paint on. Phosphoric acid is pretty safe for the metal so no worry about eating it away like HCl.

HCI? This stuff is supposed to be easy on the metal, too. I have used it numerous times already. I guess the bore scope inspection will tell. I will get some screen shots and video from it and post up the results. I don't have a tub big enough (that I could use without fear of DEATH) unless I go purchase something large enough to submerge the entire tank. Are there disposal issues with the left over liquid?

Don´t use HCL or H2-SO4, it´s a to agressiv acid!!! Phosphoric acid will convert rust FE2-O3/FE2-O4 into a zinc ZN layer.
You have to wash out/neutralize the surface of your tank with spirit alcohol to prevent flash rust.

Iron an phosphor will never produce zink.
But Phosporic acid at 20% concentration will easy eat away rust in your tank in a couple of hours. Then when you rinse the tank with water and the acid concentration gets between 3-5% iron and the phosphoric acid will react more slowly and turn into ironphosphate. Which will act as a rust inhibator long enugh for you to rinse the tank, empty it, dump half a bottle of wd40 into it, turn it around so that the wd40 covers all surfaces and then heat the tank to drive out all moisture. I usually use a hair dryer that I blow in to all openings while turning the tank around.
Dont just leave the tank sitting with moisture still in it, as it will accumulate at the lowest spot and you will have a new rust spot.

Heat, turn, heat, turn and heat along the seams.

Good luck
And no, coke doesn't work, it contains only 0,017% phosphoric acid and that concentration will not turn miracles.

/Anders

I have a couple of heat guns that I plan on using to dry the tank out. Evapo-Rust instructs to rinse with water. if you don't, it dries into a sticky film. I will pick up a gallon of WD-40 today since the soaking is ending today. My bore scope should be arriving today as well.

Bore scope arrival is pushed back until Friday (I am leaving on a 3 day trip that morning). Contemplating leaving the solution in the tank until I get back. I really want to see the inside surfaces prior to ending the soak, so I don't have to do it again if there is still some areas not treated well enough. I still have not run across any pin holes or leaks (still crossing my fingers!).

Evaporust is pretty safe for the most part, it will eat up zinc though (like your petcock.) I learned this by soaking a fuel level gauge in the stuff and it ate off all the zinc plating. Beware the same thing happening to your low fuel light sensor.

Nessism is ofcourse right, always remove the fuel tap, the fuel level sensor and the tank cap. Phosporic acid will eat away cromate and zink on metal that is electroplated and it is quite aggressive on alu.
Make blanking plates from a nylon cutting board to blank the holes for the tap and the sender and I have a silicone bung that I put in the filler hole.
The cheapest way to get your hands on phosporic acid is to buy ceramic tile cleaner at your hardware store. It usually contains 20% phosphoric acid and som detergents that will not affect the derusting process.
/A

Due to the travel restrictions placed today in California, my trip for this weekend was cancelled. Probably the right call. On a bit of good news, my bore scope showed up a day early today, and now I have an open schedule. So the tank will get drained and inspected tomorrow. I will post what I find!

With conversations about engine stands going on with some of these threads, I realized I already have the raw materials on hand. I may just need to build me one of those...