How to Clean out a Rusty Fuel Tank.


Keep er' Between the Ditches
I spent a bit of time the last few days over Christmas break on cleaning out the tank of my SL 70 Project.

I know a lot of people have covered their method of tank cleaning, but I'll tell you mine anyhow. Like most things that I do, I am sure that there are better ways, but that's never stopped any of us giving our 2 cents before... ;)

Here's a list of what I used for this project. Some of it I had laying around, so I'm unsure of the true cost. If you had to buy EVERYTHING from scratch, I'm guessing youd be around $50, but chances are you already have some of this stuff too.

  • Dish soap
  • Hot water from the tap
  • 5 gallon bucket
  • Shop Vac (hair drier will work too)
  • Small can of acetone
  • 1 gallon of Sunnyside Rust Remover bath
  • WD40, or some other anti-rust solution. Not the spray, but a bulk can.
  • Funnel to pour liquids into tank filler. I used the top cut off of a 1 gallon milk/ water jug
Here are the steps I used. There are some pics at the end.

Step 1. Remove petcock and make block off plate. I used an aluminum plate with a gasket made of parts store gasket sheet. That said, the chemicals I use are not supposed to be caustic or damaging to rubber or aluminum, but I didn't want to risk it.

Step 2. Flush the tank THOROUGHLY with hot soapy water. I probably flushed it 5 times with soapy water, then 5 times with clean water until it came out pretty "clean" and clear with as little flake and residue as possible. I had a length of chain in the tank as I sloshed the water around to help knock off the flakey rust and varnish mixture. The chemical I use doesn't eat through varnish well, so you have to get that outta the way so that it'll work on rust.

Step 3. Fill the tank up with the rust remover solution. I use "Sunnyside Rust Remover Bath". This particular gallon I've had for several years and this is probably the 3rd tank I've used it on. When I first bought this stuff, back round-abouts 2016 or 2017, when looking up the MSDS, the page header was actually for Metal Rescue or Evaporust. I cannot remember which now. It has since been changed to a "Sunnyside" header on the MSDS. It currently sells for $22 a gallon at Menards in Central Ohio. Its expensive, especially compared to some of the phosphoric options, but it works well and at least there's no acids to neutralize. Also, I was plenty careless and it didn't hurt the paint at all. This particular tank is just a hair over a gallon so it filled up with 1 gallon fairly full. In a bigger tank, I have had success with moving the tank around so that the solution sits on all the inside surfaces. It just takes longer and more work, but I am cheap, so that's what I do.

Step 4. Let it soak. The label says do not exceed 48 hours. Following instructions is for idiots and all generalities are false, including this one. I left it for 4 days. Oops. Good news is a whole didn't tear in the universe at 48:01... or maybe it did? is Rona my fault? Am I why were getting a $600 stimulus check instead of $2000? Am I why "Baby Shark" has more YouTube views than any other videos on the platform??

I Digress.

Step 5.
Poor it out. I put it back in the O.G. container to be used again. I'll strain it before using it again, as I did last time.

Step 6. Flush with lots of hot water, until it comes out clean and without bubbles. I didn't use soap, just water. (note, I don't have a hot water spigot in my basement where this went down. If so, id have just run hot water outta the tap through the tank. Instead I got a free workout carrying gallons of hot water from the kitchen sink. I used a 5 gallon bucket to dump everything into.)

Step 7. After getting all the water shook out as possible, IMMEDIATELY pour some acetone in the tank and slosh around. Its probably not the best practice, but I just covered the filler with my hand. This helps to chemically dry the water outta the tank.

Step 8. Pour out as much acetone as you can, then insert a shop vac hose in the filler neck on "blow" to dry up any remaining acetone.

Step 9. IMMEDIATELY pour in something to stop flash rusting. I personally used a splash of acetone mixed with WD-40. Enough to fill the tank about a half inch on the bottom, then sloshed it around. This tank is going to be sitting on the bench for a while as this project slowly progresses.

Step 9 Alternate. If you are a more organized and faster bike builder/mechanic than I (which you prolly are), you can replace the petcock and IMMEDIATELY fill full of gasoline in order to stop the flash rusting.

For your enjoyment, here are some pics. (Warning, first pic is graphic, viewer discretion advised)

Before Pic of the Inside of the tank. (No, that's not a close up photo of Mars....)

I like to sit the tank over a 5 gallon bucket, in case it springs a leak or the petcock block off fails. (note: this pic was actually taken before the petcock was removed and blocked off, but you get the gist)

Here is the rust Remover bath solution that I used.

This is after the acetone and shop vac "dry" but before the anti rust treatment. As you can see, if you work quickly, there will be minimal flash rust.

This is after a slosh of WD40 / Acetone mix.

Now I have a nice piece of moto art on my home office desk until I get the rest of this thing done...

I use the shop vac on suck instead of blow. Moves the same amount of air, and should dry the metal a little faster by slightly reducing the internal pressure. You can kind of judge the progress by feeling the tank and when it starts warming up, it should be near dry.
I use the shop vac on suck instead of blow. Moves the same amount of air, and should dry the metal a little faster by slightly reducing the internal pressure. You can kind of judge the progress by feeling the tank and when it starts warming up, it should be near dry.
Makes perfect sense. I'll try that next time

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