Removing rust from a gas tank can be accomplished in a number of ways. Different strategies include using abrasives such as gravel or washers, using acids such as muriatic acid or vinegar, using a battery and washing soda, using a tank coating kit, or using a combination of the aforementioned strategies. No matter which method you use, clamping a hose to the gas tank outlet hole like shown here (if possible) makes life a lot easier.
Many people recommend using nuts and bolts inside the tank to help scrape or knock off big chunks of rust. While this can be an effective way to start the cleaning process, it will probably not be entirely effective by itself. Also, doing this in a step-through moped can be very frustrating because it will be difficult to remove all of the nuts and bolts. Ice can be used as a substitute for nuts and bolts -- it will still act as an abrasive, but it will melt, which will save you from having to dig 50-100 nuts and washers out of your gas tank.
NOTE: you can use a section of chain, tied off w/ fishing line to mostly eliminate the issue of getting all the nuts and bolts out. Only problem is the rare instance when the chain works itself into a knot inside the tank.
Hydrochloric (Muriatic) Acid
WARNING: Wear protective gear during this process. All skin should be covered -- long pants/shirt, work boots, gloves -- and eye protection and filtration mask are very important because the reaction of muriatic acid and rust gives off extremely harmful vapors. If spilled, muriatic acid can be neutralized with baking soda. When working with these chemicals, make certain that you have ample ventilation. It's good to have a fire extinguisher handy as well. Always dispose of solvents / hazardous chemicals responsibly, please. And, be safe. An alternative method of using muriatic acid is explained (with pictures too!) in the blog post linked above.
- Start by removing the petcock. The aluminum body and rubber internals will have a world of woes with the acid solution.
- If you have a pressure washer, fire it up and blast out all the solidified chunks of rust/oil/fuel in the tank. If the outlet becomes clogged by the chunks, use a pair of hemostats to pull out the debris. Continue until the water runs free of debris.
- For best results the tank should be de-greased with a de-greasing solution or very hot soapy water prior to etching. Let the de-greasing solution set in the tank for several minutes and agitate as you see fit. Drain the de-greasing solution and rinse tank with water.
- Attach a piece of Nalgene hose to the outlet of the tank with a zip tie. Clamp it off with a pair of hemostats.
- ALWAYS ADD ACID TO WATER. Start with a more mild solution of 1:1, water:muriatic acid. Be careful not to get the acid on the moped (especially the paint!). Watch it to see that bubbles are being produced in the tank. Let this sit for about an hour.
- Drain the tank by removing the hemostats. Flush the tank with water.
- If necessary, repeat this process with a solution of 1 part water and 2 parts muriatic acid.
- Drain the tank by removing the hemostats. Flush the tank with water.
- In a bucket, mix about 1/4 cup baking soda to 2 gallons of water. Fill the tank, let it sit for a few minutes, drain and repeat perhaps 4 or 5 times. You really want to neutralize any remaining acid in the tank, so don't be stingy.
- After draining the tank of all available water, seal the Nalgene tubing with hemostats and fill the tank with 70% isopropyl alcohol. Let is sit for 5 to 10 minutes. The water molecules in the tank will bond to the alcohol to avoid further fuel issues. Drain the alcohol and discard responsibly.
- Seal the tubing again. This time fill the tank with straight gasoline. Let this sit for five to ten minutes. Drain the fuel and discard responsibly. You may see some minor clouding and sediments, but it should look a lot better than when you started.
- If you hadn't done so already, clean out your carburetor with spray carb cleaner and/or Seafoam. Replace the fuel line and make certain that you install a new fuel filter. It's a very good idea to have a couple spares on your shelf. Take a moment to clean your spark plug and gap it to spec.
- Fuel up your ped with perhaps a quart (max) of fuel or premix, whatever it takes. Prime the carb, say a little prayer and fire the bad boy up. Avoid long rides until you're certain that you have no fuel leaks and good fuel delivery.
WARNING: Wear protective gear during this process. All skin should be covered -- long pants/shirt, work boots, gloves -- and eye protection and filtration mask are also a good idea. Although phosphoric acid used for de-rusting tanks is somewhat less insanely toxic than muriatic acid, it's still not something that you want inhale or have spilled on you. If spilled, phosphoric acid can be neutralized with a bicarbonate solution, such as baking soda. When working with these chemicals, make certain that you have ample ventilation. It's good to have a fire extinguisher handy as well. Always dispose of solvents / hazardous chemicals responsibly, please. And, be safe.
Oxalic acid (wood bleach) can be a cheap safer alternative to muriatic / hydrochloric acid. It gives similar results to phosphoric acid , but will flash rust some if you do not neutralize it and spray the tank with WD-40 when you are done. I used 4 tablespoons per gallon of water and let it soak 24 hours. Follow the naval jelly method and it will work out great.
The Naval Jelly or Milkstone remover Method = Phosphoric Acid + Galvanizing Agent = Tank will not rust again.
Milkstone remover from Tractor Supply Company is 56% phosphoric acid. Use one quart for a 1 gallon tank — about 14% acid.
- Dump out all gas/funk from tank, rinse 5–10 times to get large rust chunks out
- 1/2 jar of naval jelly dissolved in 2 liter bottle of water
- Dump in tank (fill completely with plain water) and let sit 24hrs
- Dump naval jelly and rinse with fresh water
- 1/2 cup baking soda dissolved in 2 liter bottle of water
- Dump in tank (fill completely with plain water) and let sit 2 hrs
- Dump baking soda and rinse 2x with fresh water
- Shake all or as much water from tank as possible. Use a shop vac or compressor set to blow air. Most water can be blown out.
- Use 1/2 can or more WD-40 on tank to help emulsify water so rust wont start again
Behr Concrete Etcher and Rust Remover
This product can be used to clean rust from the inside of a gas tank because it contains phosphoric acid. This can be accomplished by completely first de-greasing the the gas tank with a commercial de-greaser or very hot soapy water. Flush the tank with water after de-greasing. Next you plug the hole where the petcock goes, and then fill the tank with the etcher (make sure you mix the etcher with water at a ratio of 1:1). It must be watched carefully so that it doesn't eat through the good metal. Next carefully drain out the etcher and rinse the tank with water. Next fill it with a solution of water and a small amount of baking soda to neutralize the acid. After 15 minutes, rinse the tank with water again and continue rinsing until the water you pour out of the tank is completely clear. At this point it is important to make sure the tank has no more water in it. This can be accomplished by getting as much water out as possible, adding WD-40 or rubbing alcohol to the tank, and rinsing it out with gasoline. Immediately fill the tank with premix to prevent further rusting.
Vinegar can be used to clean rust from the inside of a gas tank because it contains acetic acid. This can be accomplished by filling the gas tank with water and then draining that. Next, plug the hole where the petcock goes, and fill the tank with the vinegar, leaving it in overnight to dissolve the rust. After pouring out the vinegar, rinse the tank with water. Next fill it with water and a small amount of baking soda to neutralize the acid. After 15 minutes, rinse the tank with water again and continue rinsing until the water you pour out of the tank is completely clear. At this point it is important to make sure the tank has no more water in it. This can be accomplished by getting as much water out as possible, adding WD-40 or rubbing alcohol to the tank, and rinsing it out with gasoline. Immediately fill the tank with premix to prevent further rusting.
Alternatively, a salt and vinegar mixture can be used as these ingredients will react to form a weak sodium acetate and hydrochloric acid solution. This solution should remove rust more quickly than the acetic acid in vinegar alone.
The following is a documentation of a five day vinegar run in a Maxi tank by Andrew Buck Michael as posted on this thread:
I went with the vinegar/salt combo (gallon of vinegar and 1.5 cups of salt) for a mild acid that would slowly eat away at the rust, for less $$$. I emptied the vinegar out every day to take a picture and to flush it out, and only adding a new gallon on day 3. It took about 5.5 days, but it looks pretty damn good for only spending $6 on two gallons of vinegar and a bottle of salt. When I rinsed the tank, I put lots of baking soda to stop any acid. Actually i added to the vinegar to make it foam and I capped the top of the tank so it would bubble itself out of the petcock. I think this may have loosened any lingering rust because there were a few flakes that floated out. I then rinsed with water and soap several times followed by a few wishes of fresh fuel. I did not see any flash rust before I topped it off with pre-mix.
This method can work because of the acidic quality of the drink, but it has been questioned due to the sticky sugariness of it. Diet Pepsi will also do the trick just fine. Whether you use Coke or Pepsi, the key word here is Diet!! No sugar.
The Works (toilet bowl cleaner)
The Works toilet bowl cleaner is a cheap, readily available, fast, and effective product that will remove rust from your gas tank. However, the main ingredient in The Works is hydrogen chloride. Hydrogen chloride + water = hydrochloric acid = muriatic acid. If you want to use The Works, scroll back up and read the muriatic acid section above. Already read it? Read it again. The following instructions should be considered an addendum to the much more complete directions above.
If you decide to go this route, you MUST do the following:
- Remove your petcock. Petcocks are generally made out of aluminum. Aluminum and "The Works" react rather dangerously. Run a google search for "The Works bomb" if you want to see for yourself what happens. If you need something to plug the petcock hole, a piece of hose/tubing with a cork or other stopper in the end works well.
- Do not get it anywhere besides the inside of the tank. It will eat concrete. It will eat paint. It will eat chrome. It will eat rust.... which is why it works so well, but again, BE CAREFUL.
- Don't touch it, and don't breathe the fumes. This is toxic stuff.
Battery and Washing Soda/Electrolysis
Remove rust and amaze your friends with Science! Electrolysis is a technique for returning surface rust to iron. The process actually alters the tank wall on the molecular level removing the oxygen that has oxidized (rusted) the tank. This method has advantages over old standbys like vinegar, Coke, muriatic acid, naval jelly, wire brushing, sand blasting, etc. because those methods all remove material to get rid of rust. These other methods also remove un-rusted material. The electrolytic method removes only the oxygen from the oxidized metal by returning surface rust to metallic iron, rust scale is loosened and can be easily removed. Un-rusted metal is not affected in any way.
What do you need to make this work? Not much, really:
- Your rusted gas tank.
- A battery charger or other source of 12V DC power.
- Wires or cables to connect the electrodes together, lower gauge is better, less heat. Make sure it is insulated.
- Sacrificial electrodes - iron re-bar works great, stainless steel is very bad (and the result is illegal and dangerous). Go to your hardware store get some non coated steel
- Arm & Hammer LAUNDRY Soda, also known as washing soda.
- Some chains or steel wire to suspend the part in the solution - copper wire is bad and messy.
The basics are pretty simple:
- Look in your tank. Get familiar with the inside of your tank you are going to need to fit the Sacrificial anodes in there and have them not touch the edge, because it will cause you to ground out and not work.
- Mix 1 Tablespoon of Washing Soda with every gallon of water to create an Electrolyte solution. (Don't go overboard with the washing soda people. It won't help.)
- Cut your sacrificial anodes to lengths that will fit in the tank. I drilled holes at the top to attach a wire. Now use electrical tape to tape the wired end and the other end thickly so there is no possible way you can ground out on the edge. You can use more then one at a time.
- Wire all of the electrodes together so they are, electrically speaking, one big electrode. Make sure all connections are on clean metal and sufficiently tight to work.
- Suspend your part in the solution using the wire/chains so it is not touching the bottom and is not touching any electrodes.
- Attach the battery charger NEGATIVE lead to the part and the POSITIVE lead to the electrodes. Do not get this backwards! If you do, you'll use metal from your part to de-rust your electrodes instead of the other way around -the positive electrodes are sacrificial and will erode over time. That's how the water becomes iron-rich. THE POLARITY IS CRUCIAL!! The iron or stainless electrode is connected to the positive (red) terminal. The object being cleaned, to the negative(black). Submerge the object, making sure you have good contact, which can be difficult with heavily rusted objects. Get it backwards and your object will be relentlessly eaten away! Make connections on a part of your electrode that protrudes out of the solution, or your clamps will erode rapidly.
- Double check everything to be sure the right things are touching, the wrong things are not touching, and the cables are hooked up correctly.
- Turn on the power — plug in the charger and turn it on.
Within seconds you should see a large volume of tiny bubbles in the solution — these bubbles are oxygen and hydrogen (very flammable!). The rust and gunk will bubble up to the top and form a gunky layer there. More gunk will form on the electrodes - after some amount of use, they will need to be cleaned and/or replaced - the electrodes give up metal over time. That's why re-bar is such a nice choice — it's cheap and easy to get in pre-cut lengths.
The process is self-halting - when there is no more rust to remove, the reaction stops. This is handy because you don't have to monitor it, and because you can do large parts where they are not totally submersed at one time (aka, by rotating them and doing half at a time) without worrying about "lines" in the final part.
Once you are done, the part should immediately be final cleaned and painted - the part is very susceptible to surface rust after being removed from the solution. There will be a fine layer of black on the part that can be easily removed, and once it is removed, the part can be primed/painted as needed.
You're playing with serious stuff here, so stay safe. It's not rocket science, but if you're new to this, you might not know all of this - so read up before you do any of this.
- This process produces highly flammable and explosive hydrogen gas (remember the Hindenburg?), so do it outside, or in some other well ventilated area. Hydrogen is lighter than air (like natural gas), so it will collect near the ceiling - not sink to the floor like some other flammable vapors will (like propane and gasoline). If you have open flames near this (Hint: gas appliances like water heaters and furnaces have pilot lights!) you will most likely severely injure or kill yourself (and others near you) and become a contender for the Darwin Awards in the process.
- Assuming you used re-bar and steel wire/chain like you were told to, the waste water resulting from this is iron-rich - it's perfectly safe to pour it out onto the grass and your lawn will love it. Beware of ornamental shrubs that don't like iron-rich soil though, unless you like making your wife mad at you.
- Make sure the battery charger (or whatever source of power you use) stays dry. All of the usual cautions about any electrical device in a wet environment apply here.
- The solution is electrically "live" - it is a conductor in this system. Turn off the power before making adjustments or sticking your hands into the solution. You can get a mild shock if you stick your hands into the water with the power on.
- The solution is fairly alkaline and will irritate your skin and eyes. Use gloves and eye protection. Immediately wash off any part of your body the solution comes into contact with with plenty of fresh water.
- Don't use stainless steel for the electrodes. The results are toxic and illegal to dump out.
- Don't use copper for the electrodes and anything else in the water - the results are messy.
- Remove finger rings - if you short across one they instantly hit about 1200 degrees.
If you are unsure of any of this or unsure about your safety - STOP! Get help before you do something stupid. Use common sense, be smart about what you're doing, and stay safe so you can finish your restoration project and enjoy it.
If you're like me and cannot find Laundry/Washing Soda in the stores, you can 'cook' your own following the instructions here.
Edit by Rdhawg 11/27/13 Did my tank by itself. Clamped one lead to the petcock, made an anode that fit in the fill spout (Left room for flushing around it) with the other lead attached to it. Filled tank to the top with electrolyte solution. "cooked" it for about 24 hours. Flushing the fill spout area frequently and cleaning my anode with a wire brush about every hour. Worked great. When done I flushed with clean water and a bunch of nuts rattled around inside. then dried it with a blow dryer. After I poured a bunch of 2 stroke oil in and rolled it around to coat everything at least till I get it full of gas.
Kreem is a commercial product for coating the inside of a tank with a chemical compound resistant to the corrosive effects of gasoline. It's available as a fuel tank liner kit, including tank prep chemicals. One thing to note is that it's a bit more difficult to use properly than is initially apparent. For one thing, it's extremely sticky and viscous. Also, it's hard to get an even, thin coat without cutting your tank in half. Overly thick coatings result in flaking, which will clog your petcock or filter, or worse, destroy your carburetor jet etc. However, when done professionally, it is effective for many years.
See also, this forum thread on removing Kreem from a gas tank.
POR has a cycle tank repair kit available that includes all the chemicals to clean, prep, and coat a tank. The most challenging part of PORing tank is the tedious drying process. After the cleaning and prepping, which adds a charge to the metal so the coating will adhere to it, the tank must be completely dried. If this step is not done correctly the entire process will fail. The most effective ways to dry a tank seem to be running a source of hot air through it, while setting it out in the sun. Once the tank is dry, the coating may be applied. Once dry, the tank will last for years without worry of rust (some user's have experienced 15+ years of no rust). POR is highly recommended above Kreem, as Kreem has a tendency to fail after time, while POR does not (when done properly).
Evapo-rust and Rust Release are "green" rust removers because they are not harmful acids and they do not create harmful fumes. It can be dumped out onto gravel when you're finished using it, which can save you the hassle of storage or paying to remove the acids stated above. The other good thing about Evapo-rust and Rust Release is that it is only designed to eat rust and not metal, so you can leave it in your tank for over 24 hrs without burning a hole through the metal. The downside is that it was necessary to leave it in the tank for 36–48 hrs to get it about 90–95% clean.
I followed the same steps stated above: Drain old gas, remove petcock, de-grease tank and do a post-de-greasing rinse, use Evapo-rust or Rust Release, fill it with nuts and bolts to knock off loose rust, wash it out, fill it with Isopropyl alcohol, drain that, flush it out with gasoline a few times (drain and store). After all that, buy and install a fuel filter as a precaution.
It went from thick rusty sludge to barely any sediment running through my fuel line. You can buy Evapo-rust at Autozone (check their website for other retailers too), but the employees don't know that they have it, so tell them it is probably locked up. It also may be in the paint aisle. It is roughly 10-13 bucks per liter, and usually comes with a 3 dollar mail in rebate. 3-4 liters Should work, but depends on how big your tank is. Also available at Amazon.
Money saving tip: You can buy 2 liters instead of 4, then , tip your bike forward to make sure that the cleaner gets into the part of the tank that is closest to the stem, tipping the bike back every 4-8 hours, repeat, occasionally sloshing the cleaner back and forth. This obviously isn't the easiest way, but, it is very rewarding. You can also buy Evaporust at Tractor Supply.
Wood Bleach ( Oxalic Acid )
Oxalic acid, sold as wood bleach . Oxalic acid is a lot safer to work with, but still requires due caution (READ THE LABEL). It's not nearly as toxic as muriatic acid. It does NOT harm painted surfaces. It just eats rust and leaves a protective coating on the steel after being thoroughly rinsed with water.
For good description check out this forum thread.
J.B. Weld (for petcock repairs)
J.B. Weld is a welding substitute/epoxy. When cured, it is water, petroleum, chemical and acid proof. In rare cases, the petcock may take an impact which may break the weld on the threaded tube jutting from the gas tank. When this happens, the petcock appears to be leaking, or gas leaks from inside the frame and onto the engine. Because there is no way to weld on or replace the tank, it must be repaired likewise or the frame replaced. Removal of all gas and application of a degrease compound is essential in preparation for use of J.B. Weld. While it may be impervious to gas after curing, before cured, gas and oil will compromise the epoxy, grasp on the tank wall and crack. From personal experience, degreasing and riding around for about a month (with external tank) was enough to clear out and clean the tank. A generous amount of J.B. Weld should be mixed. Rough the inside of the threaded tube as best you can with a dremel tool for best adhesion. Bending a long wood screw (torch applied) at a 75 to 90 degree angle will allow you to rough up somewhat the inside back of the tank wall you can't see and be useful later. Pack the epoxy down inside the threaded pipe jutting from the tank. Once this is done use the bent wood screw to smear the epoxy all around the inside back of the tank where the tube is welded on. Before the epoxy cures, plug the tube with an assistants finger or other and create a seal around the fill hole (where the gas cap is) and use an air compressor to create pressure in the tank and hopefully blow epoxy into the cracked weld. Afterwords let cure for suggested time on box before applying pressure to the threaded tube or filling with gas. THE EPOXY WILL HARDEN AFTER FOUR OR FIVE HOURS BUT DO NOT FILL WITH GAS UNTIL FULL CURE TIME HAS ELAPSED. Hopefully when you fill your tank up it won't leak. If not, repeat the process, buy a new frame or get happy with and external tank.
AN edit/comment from Gabe:
Thanks for all the tips and research on getting the rust out of gas tanks!
I don't want to crap on your advice, but JB weld does not work in any application where it is exposed to gasoline no matter how well you clean it. I tell you this from experience. gasoline dissolves it no matter what the manufacturer claims. I don't think it is the ethanol either. the only successful patch to a gas tank using an epoxy resin was where I plugged the hole with wax and then used JB weld over it. it lasted a couple of weeks. best advice is to weld it or use brass solder if it is very thin iron. and don't be afraid of it blowing up. let it dry out overnight or blow some air through it to dry it and get the vapors out and it will be fine. test it with a match or a torch first if you want to, and keep the gas cap off.
JB weld works great on aluminum of plastic parts of radiators! I had it come loose once also where it was exposed to transmission fluid (high detergent oil)
For plastic gas tanks with a leak I have used a soldering iron or a hot flathead screwdriver to melt a hole shut. I also used the technique on a leaky plastic canoe once. another useful technique is to use a filler plastic. I have used ice ream pail lids cut into strips to patch gas tanks. I lit one end of the strip on fire and let it drip over the crack. It worked great on more than one leaky tank. But one time it didn't. I think there was some kind of incompatibility in the two kinds of plastics. it's worth a try.
Thanks for all the tips and research on getting the rust out of gas tanks!