The finishing.com Hotline -- Serious Education ... plus the most fun you can have in metal finishing
Muriatic Acid for Fuel tank cleaning?
Q. I am restoring a Porsche that has been sitting idle outside for about 7 years. I am at the point where I need to clean the fuel tank and get the rust out of it before using fresh fuel and possibly burning up a rather expensive fuel pump. I have heard that muriatic acid was the way to go but haven't found any literature on 1: How fast acting is it? 2: Will it clean all the rust that is in the bottom of my tank? 3: Is there actually a safer product that will do the job just as well?
I have been restoring cars for some time now but this is the first time that I haven't just replaced the tank because of the expense involved. I would appreciate any advise or comments.William M [last name deleted for privacy by Editor]
Hobbyist Auto Restorer - Georgetown, Texas
A. Muriatic acid is a weaker mixture of Hydrochloric acid, don't let that fool you, it is still very potent stuff and should be handled with the utmost care. In regards to your idea for cleaning the tank with the acid I can say that yes, it will eat the rust out of your tank, and then promptly let it rust back up again, very very quickly, about 30-45 minutes you will have rust on it again. You will need to seal the tank (possibly fiberglass?), very quickly after using the acid. Overall I think this is a bad idea and you would be better off getting a new tank, but there is my prediction and suggestions for you.
Good luck with the PorscheMarc Banks
- Elizabeth City, North Carolina
A. I would caution you about using hydrochloric acid on your fuel tank. While it will do a good job dissolving the rust, you may uncover holes you didn't know you had. In addition, you will need to rinse the metal very well to remove the chlorides that can cause more corrosion. I recommend using the least aggressive method possible. I assume this rust in on the interior of the tank. If it is light rust, phosphoric acid or citric acid will do well. Try a 10% (w/w) solution and drain and rinse well after 60 minutes. Temperature is important too. Batch the solution using hot tap water and try to keep the tank at least warm throughout the process. Good luck.Joseph Lockrem
- Indianapolis, Indiana
A. As you can see, no one here thinks derusting with muriatic acid is a good idea. Muriatic is too aggressive, and you will have a subsequent rusting problem. There are two good approaches. 1). You can buy a kit which contains cleaner, deruster, and tank coating materials, and do the job yourself. I used this process on my AH tank fifteen years ago, and it is still fine. 2) You can send your tank to a company which will derust and hot dip galvanize it. Either of these methods will prevent future rust and seal small pin holes. Get a copy of "Hemmings Motor News" [link is to product info at Amazon]. You'll find both advertised there.
Jeffrey Holmes, CEF
- Spartanburg, South Carolina
A. Hi William,
What Marc suggested about fibreglass seems to be a good idea.
However, this does mean REMOVING the tank first of all.
Having done that and 'cleaned' out the insides, then I'd suggest you clad the whole outside with at least one layer of mat plus a suitable fibreglass resin (Isopthallic may not be good enough chemically speaking, go for a vinylester due to its better flexibility over a Polyester). This should cover, as Joseph said, any 'holes'.
Maybe you should 'coat' the inside of the tank first of all. Ask your friendly local frp shop for some advice. They might well suggest a THIN vinylester coating by pouring it into the tank and sloshing it around ... maybe that should be first thing to do. Thinning done with Acetone [linked by editor to product info at Amazon], I believe.
Re hydrochloric, have a gander in the archives at # 12044 which might/might not be useful.
I did use fibreglass on my rear muffler ... the Volvo's rear muffler didn't last too long in winter/salt conditions. It worked out A.OK. ... but that was in Ye Olden Days of the 70's.
- White Rock, British Columbia, Canada
(It is our sad duty to advise that Freeman passed away April 21, 2012. R.I.P. old friend).
Agree with David. For $55 you can't go wrong.
Jeffrey Holmes, CEF|
- Spartanburg, South Carolina
A. You can use 5% citric acid solution (or 50 gm citric acid/1 lit water/+ some ammonia, pH must be 3,5)! Rinse well! Much better and safer than muriatic acid! Good luck!Goran Budija
- Zagreb, Croatia
A. I can vouch for the POR-15 fuel tank repair kit [linked by editor to product info at Amazon] , and have used it in motorcycle fuel tank restoration. In addition to the kit(which includes a metal etching chemical), however, I have also used muriatic acid to remove rust from the inside of the same tank. The muriatic acid(1 qt for a 6.5 gallon tank) was put in full strength and the tank was then "rolled" for about two minutes. I immediately drained the acid into a drain pan, and rinsed the tank for about 5 minutes. Then dried the inside of the tank with hot air. As soon as it dried, the POR-15 was applied. The muriatic acid was then poured from the drain pan into the original container for proper disposal at the municipal hazardous material disposal center. The muriatic acid did a great job of removing the rust, as, overall, the inside of the tank looked like bare metal.
One word of caution regarding the POR-15; if you have any small passages(in my case the tank crossover tubes), insert a wire cable prior to applying the POR-15, as it hardens like iron, and those passageways will be impossible to clear. Let the POR-15 cure (4 days), and pull out the wire cables.
Good luck,Johann Uhrmann
A. Try Eastwood. The company has it all for restoring cars (including gas tanks)Pete Ross
- Portsmouth, Virginia
A. FYI, muriatic acid can be neutralized with baking soda [linked by editor to product info at Amazon]. It must still be properly disposed of, but neutralizing makes it much safer.Bob Nauta
- Nunn, Colorado
A. Muriatic/Hydrochloric Acid is just HCl + Water (not sure of the dilution).
Add Baking Soda (NaHCO3), and one gets NaCl + H20 + C02...
I.e., when one neutralizes HCl with Baking Soda, one gets a resulting mixture of Water, Carbon Dioxide, and SALT, none of them are considered caustic substances. If "pure", it would require no special handling.
That doesn't mean that the sludge that you are picking up isn't caustic.
You might note, your own body makes and regulates Hydrochloric acid (stomach), and regulates the sodium and carbonate levels quite effectively.
- St. Louis, Missouri
A. Suggest you look at a product POR-15 [linked by editor to product info at Amazon] I had a rust problem in the fuel tank of my Austin Healey which I treated with POR 15
I was quite impressed with the result.
- Brisbane, Australia
I have used Muriatic acid and it works great. I don't see the big deal about the stuff, dump it along the fence as I also do with used motor oil. It makes a great edging solution and I don't have to weed it. I really think everyone is going way over board about the environment stuff as if this is the worst thing that is being done to the Earth in each person's daily life.Jason Heights
That was probably a put-on, Jason, but just hope you never have to sell the property. Not sure about Florida, but in most states all that earth will have to be excavated and disposed of. The muriatic acid probably wouldn't last for too many years, but the oil will be around for many decades.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
A. THERE ARE A NUMBER OF OTHER PRODUCTS THAT WORK JUST AS WELL. Ospho [linked by editor to product info at Amazon] FOR ONE WORKS GREAT AND ANOTHER IS CALLED Rust Bullet [linked by editor to product info at Amazon]. RUST BULLET "KILLS" THE RUST AND TURNS IT INTO A PRIMER. IT SAYS IT WILL LAST FOR 10 YEARS Guaranteed BUT I DON'T KNOW about INSIDE A FUEL TANK. ANYWAY, YOU CAN CHECK THEM BOTH OUT. HOPE THIS HELPS!JEREMY MORGAN
- WESLEY CHAPEL, FLORIDA
Q. I have a gas tank that I am redoing. It was in an accident and someone was going to fix it and didn't. It has been sitting with no paint or any coverage for 2 years. There is start of rust. Should I remove the rust before I Naval Jelly [linked by editor to product info at Amazon] (Big project), or will the sanding after Bondo [linked by editor to product info at Amazon] take care of it?Joan Cooper
hobbyist - Orangevalle, California
A. I just got off the phone with Rust Bullet, and was told that their product can NOT be used for the inside of a fuel tank.Scott Flanders
- Gig Harbor, Washington
May 18, 2008
A. Have you ever tried Naval Jelly [linked by editor to product info at Amazon], it destroys rust and washes off with waterDanny Roberts
- Lawrenceville, Georgia
August 18, 2008
Q. I am planning to clean out the front and rear fuel tanks on my 1944 Ford F250 diesel truck. I will drain them, remove them, wash with Purple Power [linked by editor to product info at Amazon] cleaner and a pressure washer.
If it rusts I am planning to use muriatic acid . What effect does muriatic acid have on the internal finish (aluminum)? - Thanks
- Atlanta, Georgia
September 5, 2008
A. I have used muriatic acid for rust on motorcycle tanks. Of course, these petrol tanks can easily be removed.
I use 1:2 dilution with warm water and get good results in about an hour.
I then neutralize by rinsing with common dish soap and water. Rinse completely, and blow out with compressed air.
I then immediately coat the inside with two-stoke oil and rinse out with cheap gasoline. The tank is then ready to fill with fresh premium.
I guess they're all right for car tanks, but I have had bad results with tank liner solutions. The stuff never seems to set completely and causes paint on the outside to blister.
- Madison, Tennessee
November 2, 2008
A. You guys are missing the boat. BIG TIME. I worked in the steel treatment industry for years and Phosphoric acid is the way to go. WHY ...... The FeO3 with be removed and a Phosphate coating with convert the FeO3 to a higher resistant to corrosion surface. Used to treat metal before painting for years. So go with a 5% solution, heated to 140 F. Follow with water rinse and then alcohol rinse.
Tank will appear slightly gray in color if done correctly. Google Phosphate coatings for more info.
- Waynesboro, Virginia
August 31, 2009
A. The issue of disposal of muriatic acid should not be a problem. After use it is easy to neutralize the acid with sodium bicarbonate (baking soda) or sodium hydroxide. In the first reaction you yield CO2 Salt and Water.
HCl (muriatic acid) + NaHCO3 (sodium bicarbonate) --> H2O (water) + CO2 (carbon dioxide gas) + NaCl(Table salt)
In the second reaction you yield salt and water
NaOH(sodium hydroxide) + HCl(muriatic acid) --> NaCl(table Salt) + H2O(water)
There is no problems with disposing of this into most city sewer systems (it's just salt water). The only issue to be aware of is ensuring the material is completely neutralized. This is much easier with sodium bicarbonate because as it is buffered, so you can add too much of it and end at an acceptable pH. With Sodium Hydroxide you can create a very high pH mixture which can also be dangerous. In either instance, most water treatment plants prefer between a 7 and 10 pH. You can test this will relatively inexpensive pH strips.
Always follow proper neutralization techniques when working with acids and bases - Neutralization releases energy, so when you neutralize a solution quickly you generate a potential for explosion, and trust me... exploding acid all over you and your equipment is dangerous (and destructive).
These neutralizations are very common, and information about the techniques involved are very readily available online.
- Central Point, Oregon
March 18, 2010
A. Like Johann U. in Michigan said, I will vouch for POR-15 fuel tank repair kit. Just finished my 25th gas tank, thank you Daytona Bike Week!
Only thing I did different was first I used the Marine Clean [linked by editor to product info at Amazon] which is a very good product, it does remove any old fuel tank liner and varnish and a "small" amount of rust. I was out shaking tanks like crazy and rotating them. Usually let them sit for 24 hours then rinsed them out till they didn't feel slippery.
Then I still prefer to still use Muriatic Acid, pour a quart in raw, non diluted and added about 100 daisy bb's, and just shake the gas tank around for 4 minutes turning it constantly.
This will remove all of the rust. It's just a pain in the ass trying to get all the bb's out. Then rinse it for like ten minutes to get all the Muriatic Acid out. This stuff is very dangerous, you must wear protective gloves gloves and put goggles on cause it will burn through your shirt and your skin in seconds and hurt like hell.
Then I dry the tanks out with a heat gun, use a hair dryer if you don't have a heat gun for like an hour.
Then tape of the drain and air plugs and pour in the POR-15 Metal Ready and duct tape off the cap hole and roll it around for like 5 minutes. Then turn the tank on its side for 30 minutes a side for no longer than 2 hours as the instructions specify. Rinse the tank out several times then back to the drier for at least an hour.
Then pour in the tank liner and let it dry. And walla! You will have a just as good as brand new gas tank. I just did 25 this week and every one looks as good as the other.
Just remember that rust will flash in seconds, so plan on doing your tank project when you have 4 hours of free time.
- New Smyrna Beach, Florida
July 31, 2010
A. A chain or old nuts and bolts, shaken inside to remove pieces of rust, 50/50 mixture of normal swimming pool acid called hydrochloric acid and water poured inside for about 3 hours to remove all rust,rinsed with water and thereafter with acetone to remove all traces of water and your problems are solved-Andrew of South Africa.Andrew Pietersen
- Roodepoort,South Africa
December 12, 2010
Q. I had severe rust in my gas tank, could this cause damage to my fuel injectors? I just put in a used motor, ran great for first 20 miles then lost all power just like the first motor, I pulled the tank to replace fuel pump and noticed the extreme rust, replaced the tank, pump and filter but the engine running very roughLes Daniell
just me - Lubbock, Texas USA
June 4, 2011
A. I'm in process of rehabilitating a John Deere E35 edger (Kawasaki engine) with SEVERE internal fuel tank rust and some pitting on top around the breather holes. Many gardeners consider the JD E35 the Porsche of edgers.
Had no time to go to store so used ordinary household vinegar (glacial acetic acid, I think) and a bunch of nuts and bolts followed by water rinse. Got out most of the rust but got a light film of yellow corrosion, probably not enough to foul the rebuilt carb.
Found a university extension site that OK'd pouring out the vinegar on the lawn.
Also tried CLR after 66 yr. old neighbor told me he used Red Devil Lye for the job as a boy, but one has to certify they are a saponificator to get this methamphetamine ingredient today. I buy my soap at Walmart.
I may could try the Phosphoric acid trick above, before reassembly and use.
- Durham County, North Carolina, USA
June 6, 2011
Hi, Paul. Thanks for the info.
Two small corrections:
Vinegar is rather dilute acetic acid, whereas glacial implies 100% strength;
Lye is still readily available; drain cleaner crystals are often lye. It's dangerous stuff but has a very common household use.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
July 29, 2011
A. Look at a product called Red-Kote fuel tank liner by Damon Products. It can be found on the internet and eBay =>
- Thomasville, North Carolina
September 3, 2011
A. The tractor restorers I talk to tumble their tanks with sharp hard pebbles, any kind of small granite or marble chips from the garden center. It's easy enough to make a tumbling jig for your tank. Or if you have a pickup truck with bad shocks and bumpy dirt roads just put the tank and pebbles in there for a few weeks, turning occasionally.Greg Reid
- Millerton, Pennsylvania, USA
February 17, 2012
I have an old Suzuki Motorcycle that once had a rusty gas tank. My buddy told me to use this stuff called Muriatic Acid (with which I was unfamiliar). The first time I messed it up and it rusted all over again (because I did nothing afterwords). The second time around I managed to get out all the rust, I washed it out with a ton of water, took a hair dryer to it, and pumped in a bunch of WD-40. Well, 2 years and 4000 miles later I see no rust in my tank. So something must have worked! And on a lighter note, don't inhale the yellow smoke. That's what you call toxic.Ryan Naro
Hot Rodding - Loveland, Ohio USA
May 30, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. Hobby is car restoration and I am wrestling with a problem of removing rust from the inside of a Porsche fuel tank. I had it professionally done but am unhappy with the outcome. Examining the internal surfaces I see some black rust patches (probably neutralised) and quite a lot more brown patches, apparently not treated. The tank has a relieved area to accommodate part of the spare wheel. As a result of this it has complex interior surfaces.
I plan to prepare about 5 litres of muriatic acid solution of 1:5 (hot water) to give enough volume to cover all surfaces with some rotation. I would leave this in for about 30 mins rotating each few minutes, then flush with water and neutralise with solutions of baking soda flushing finally with fresh water.
At this point I am considering introducing phosphoric acid to coat the entire internal surface.
I would appreciate your opinion on the ratio for the solution of phosphoric acid and the length of time to leave it in the tank. I presume final flushing with fresh water and drying would be needed to prevent further rust.
- Eltham, Victoria, Australia
June 1, 2014
A. Try 5% ammonium citrate solution (pH 3,5) ... Much safer and better for you and environment ... Hope it helps and good luck!Goran Budija
June 3, 2014
The ammoniated citric acid works great on stainless steel, but is it effective on mild steel?
- Colorado Springs, Colorado
June 4, 2014
A. Ammoniated citric acid or ammonium citrate 5% pH 3,5 must work on mild steel too. Hope it helps and good luck!Goran Budija
December 1, 2014
A. Hey guys, here is the easy answer. Use a 5-6 meter thick dog chain. Shake the chain around in the tank to get the worst rust out. Wash out the tank with clean water. Use one bottle of Deoxidene - Rust Cleaner. Tape up the filler hole and shake around vigourously till it foams. Alow to dry in the sun. Wash out using three liters of fuel. Works for me!!Kendall Williams
- Cape Town, South Africa