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Rusty gas tank


Hidey Ho
Feb 8, 2022
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I have a 1978 DT250 basket case project bike I am working on. The fuel tank has some corrosion on the inside. I wouldn't be surprised if there were a few pinholes, but I've never filled the tank to see if it leaks.

What is the best way to clean and seal the tank? I am thinking of using Evaporust and some new nuts/bolts in the tank for a shake and clean method until rust stops coming out of the tank. Then seal it. I have experience with POR15 products so I was considering the POR15 fuel tank sealer, but I see there are a lot of other options out there. My biggest fear is dropping some product in the tank that wont work.

What is your experience?
I Like the Molases and water option get normal equestrian molases available from stock feed outlets. and mix 9 parts water with 1 part molases you can mix it stronger even 3 to 1 but the weak mix works and i never saw an advantage that was worth the extra cost.
This method has no abrasion no physical effort worth mentioning and its quiet and dust and chemical free.
Fill the tank leave it three or four days then check to see what the tank looks like wash out the tank imediately you pour out the mixtre. the orangey gloop will dry to a crust fairly quickly if you leave it long unwashed i just use hot water and washing up liquid but i have used just hot water before and it moves it just take the time for a extra rinse or two. Check see if the tanks clean if you are not happy just repeat until its clean two or three goes in my experience moves even the worst rust.
You could try the old handfull or small bolts and nuts with a half pint of vinigar method first to free the lose rust if you wanted then use the molases mix but realisticaly i just go straight for the molases method myself.
I have another thread on the old forum where I cleaned out the tank on a XL500S. There's more details there is you want to Google it, ( Shinyribs XL500S Advrider and it'll pop right up) but here's the short version. After trying all the different tricks through the years ( electrolysis, vinegar, etc) I was tired of tinkering around and just wanted results.

Muriatic attacks rust like rust owes it money. It'll clean out the tank in minutes. No matter how fast I came back in with a baking soda neutralizing rinse it would flash rust. But you can buy a product at Lowes called Prep n Etch ( phosphoric acid) that will knock the flash rust off within seconds. Just keep swirling that stuff around in the tank until it evaporates and you don't have to worry about flash rusting as it will do a conversion process and actually halts the rust. You'll know it's done when it see the flash rust dots turn in to a chalky film. You can go straight to using the tank then. The whole thing can be done in 15 minutes being careful not to spill. The acids aren't depleted after use, do you don't have to dispose of them. Pour then back in to their container and reuse next time.

Liners, I'm no help. I've removed more than my share, but I've never installed any.
I just cleaned up a Triumph tank, first removed the shitty lining with acetone then filled tank with vinegar, tank is clean and ready to use.
Oh ya h2o when cracked is a stoichiometrically correct air/ fuel ratio! Dont ask how I know. Ventilation is reqired and no sparks or flames.
I had fair luck with citric acid- works slowly and not as aggressive as muriatic acid but disposal is easy and low investment.

Line a trashcan with a trash bag, fill with water. Remove all the tank fittings, bag the tank in 2nd trashbag along with a few lbs of citric acid powder, float that in the trashcan. I used about 1lb of powered citric acid per gallon of tank capacity. Add water to the 2nd bag (ensuring the citric acid powder is dissolved), so it sinks inside the 1st. Only a few gallons will be needed- enough to fill the tank plus a bit extra.

The idea is to add enough water to the 2nd bag so the tank floats just below the water level in the trashcan- that way the acid is contained inside the 2nd bag, filling the tank, without dissipation in 50gals of water. Floating the 2nd bag w/ tank in the 1st avoids tearing the bags. Placing a small rock or similar on top of the 2nd bag helps to ensure it stays below the trashcan's water level. Wear gloves and eye protection when messing around in the 2nd bag.

Leave it out in the sun and once a day circulate the acid by slightly raising and dropping the tank inside 2nd bag, so acid flows in and out of the tank. Maybe flip the tank if possible so any air pockets dont stay in the same place. The citric acid is well-behaved, easy enough to let it run for a week without concern about paint and so on.

To shut it down, cut open the 2nd bag while submerged, which dilutes the concentrated acid into the main water- remove the tank and immediately rinse. I didn't put in liner but fogged the tank with oil. Empty a couple boxes of baking soda into the acidic water to neutralize the acid a bit, then dump it.
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