Gas tank rust

What's the best most cost effective way to clean inside of it?

 

That depends entirely on how bad the rust is, and how soon you want to deal with cleaning it out again. Phosphoric acid is my go-to for most situations.

 

It's not bad and I can do it whenever.. how do you go about phosphoric acid?

 

Not super easy to find phosphoric acid around me

 

here ya go
http://www.homedepot.com/p/Klean-Strip-1-gal-Phosphoric-Prep-and-Etch-GKPA30220/100406369

 

Thank you.. so do you have to neutralize it somehow after using acid?

 

shake some water around in it, maybe twice then drain it and dry real good. especially the seam, that's where it will stay wet and where most of the rust is. a heat gun works well.
do you plan on sealing it ?

 

Yup I have caswell two part and where is the seam exactly?

 

Anyone ever simply poured Evaporust in a tank? I have a moped with a one gal tank full of heavy surface rust. I'm thinking of just filling it up and letting it sit for a day or so.

 

the ridge that runs around the bottom inner edge of the tank. by the fuel valve. where people put the car door edge guard, yuck.
when you take the fuel valve off, you'll see it

 

guys that restore old tractors seem to like molasses and water mixture. sounds strange but they say is the best for big things

 

http://www.practicalmachinist.com/vb/general-archive/rust-removal-using-molasses-90452/

 

Discard what I'm recommending then. Follow Caswell's directions EXACTLY. They have a good kit, but proper preperation is vital for it to be successful.

 

A good article on fuel tank rust removal, just beware of the chemicals, safety first eh.

http://www.realclassic.co.uk/techfiles/petrol_tank_cleaning_and_rust_removal.html

 

like K-moe said, if you use a kit follow their instructions.

 

I used POR-15 on my XJ550R tank. Coating looks good except for one side of the tank where it seems to have pulled away, but not in in a flap, more of a bubble. I'll have to yank that off sometime so crap doesn't get trapped behind it.
My recently acquired FZR1000 has some mild rust in much of the tank and a few patches where it looks flaky. In the picture, there's a patch near the sender unit.



I was thinking either letting MetalRescue sit in the tank for a while and eat the rust away, or this method w/ electrolysis. I'd have to make up electrodes that fit in to the fill cap opening. The negative that's a ring that touches the sides of the opening and the anode that sticks down through the middle. I'd probably 3d-print a spacer to keep everything in place, but allow me to see inside to check the progress.

 

Evaporust will work, just have to make sure that all areas stay wet all the time or you will end up with an etch line. If it will hold the stuff, fill it up and let it sit for 8-12 hours and then check it.

The reason the POR-15 pulled away is from moisture. I had the same problem in my last attempt. My next tank coating will be done after a thorough torching. That urethane is a water-cure poly so if there is any amount of water in leftover rust pores or in seams then it will not adhere, it will set and roll off like rubber.

 

Not trying to contradict k-moe but I would be inclined to stay away from using phosphoric acid. I've used it on steel furniture I've built, and while I think the furniture came out beautifully, it was a pain to get all of it off, to get it to stop attacking the metal, even days later.

 

Keep in mind that acid treatment will eat good metal as well as the rust. I’ve used the phosphoric acid treatment and it works well. Follow up with baking soda solution to neutralize.
I’ve also used electrolysis. It works, too. I found it maybe too much work.
Metal Rescue or Evaporust are excellent choices for removing some rust from the bottom of the tank. They won’t damage good metal.
If you’re using the Caswell liner, you can buy 5 lbs of resin rust cutting media at Harbor Freight for pretty cheap. It looks like little green pyramids. Put a couple pounds in it and rotate in the dryer for an hour or two. I put the tank in an old sleeping bag then stuff the drier with pillows. Vacuum out the dust when you’re done. Rinse with alcohol and it’s ready to run or install Caswell.

Don’t screw up the Caswell liner. I don’t think you can remove that stuff.

I hope this helps.

 

Prep, and cleanup both matter when using any treatment. You can't just leave the acid on the metal and expect that it won't keep chooching away. You have to do a throrough clean-water rinse (or rinse with a base as JetmecMarty reccomended).

The second step of Parkerizing is an acid etch, followed by a hot water bath to rinse the initial acid off.

The Caswell liner can be removed, but it's a hassle and involves the liberal use of MEK.

Prep, prep, prep.
Process, process, process.
Be thorough.

Rust is a cat of many skins.