Need to clean fuel tank - AGAIN

[Dr.Jeff]

That goo toward the bottom does look similar to what I had. And there appears to be rust - but that might be in part due the camera (they seem to make things look worse than they are). I can see how that goo would contaminate the pump and rest of the system.

I'd recommend following the tank cleaning procedure I outlined earlier. Putting fuel in it won't really help; it is too similar to the chemical composition of what's there and isn't strong enough to cut it. And don't follow my lead by taking shortcuts. As for the agitation, the rust does not appear to be really deep (hard to tell from the pic). If there isn't a thick crusty layer of heavy build up and rust (mine was up to an inch thick in places), then it won't need excessive agitation. Just enough to knock off the loose stuff. That helps to speed up the acid process.

I don't think that type of pump can be disassembled/serviced without sacrificing it. If fuel is coming out clean then you should be fine. One way to give it a little rinsing without wasting a lot of fuel is to add a big filter and run the fuel in a loop back through it.

The engine on mine was running (poorly) when I got the car. So now I wonder how badly the rest of my fuel system is contaminated. It just had the fuel injectors, pump, filters, etc replaced a year prior, but was then driven with the tank like that. So everything is likely ruined again - shame. However the engine also had a bad head gasket with coolant in the oil pan, therefore the fuel system may be the least of my worries.

 

[dllubin]

That goo toward the bottom does look similar to what I had. And there appears to be rust - but that might be in part due the camera (they seem to make things look worse than they are). I can see how that goo would contaminate the pump and rest of the system.

I'd recommend following the tank cleaning procedure I outlined earlier. Putting fuel in it won't really help; it is too similar to the chemical composition of what's there and isn't strong enough to cut it. And don't follow my lead by taking shortcuts. As for the agitation, the rust does not appear to be really deep (hard to tell from the pic). If there isn't a thick crusty layer of heavy build up and rust (mine was up to an inch thick in places), then it won't need excessive agitation. Just enough to knock off the loose stuff. That helps to speed up the acid process.

I don't think that type of pump can be disassembled/serviced without sacrificing it. If fuel is coming out clean then you should be fine. One way to give it a little rinsing without wasting a lot of fuel is to add a big filter and run the fuel in a loop back through it.

The engine on mine was running (poorly) when I got the car. So now I wonder how badly the rest of my fuel system is contaminated. It just had the fuel injectors, pump, filters, etc replaced a year prior, but was then driven with the tank like that. So everything is likely ruined again - shame. However the engine also had a bad head gasket with coolant in the oil pan, therefore the fuel system may be the least of my worries.

That literally does sound like the fuel system is the least of your worries.

I was doing some research on cleaning tanks tonight and one of the more popular recommendations for removing varnish and old gas gunk was OxiClean or cheap imitations of OxiClean. Apparently, the key ingredient is sodium percarbonate. I'm thinking of using it as the next step (the gasoline today was all I had handy). For real bad cases, acetone is used as the final step for the varnish removal. Phosphoric acid was widely recommended to address rust and provide a protective barrier, but not as a primary means for removing petroleum byproducts. I'll try it once I get it clean enough.

Yes, the rust in the tank is overemphasized quite a bit in the photo. Might be the lighting and/or the varnish over the rust.

 

[Dr.Jeff]

I'm not convinced this goo is from fuel varnish. It seems more like a growth or organic byproduct of some type. So it may require a different approach than most tank cleanings. I wondered if good old bleach might kill it?

I'll be curious to hear what you find with those 'Oxi' products. I've used oxalic acid ("wood bleach") to clean out really bad radiators and cooling systems (block, etc). It strips away all of the heavy build up that clogs things up. It has a somewhat similar chemical property as sodium percarbonate (mostly concentrates of hydrogens and oxygens). Not sure how it would work here.

The phosphoric acid seems to have removed this goo stuff from my tank. But it was slower than cleaning a tank that is just rusty. As I noted, it appeared to loosen the goo and put it in suspension in the acid mixture, rather than completely dissolve it. So the goo washed out with the acid. But it also pretty much ruined the acid from future use for anything else (cross contamination).

When I cleaned the other tank (non-Fiat) with the "tar" in it (from dissolved rubber/plastic components), I found carb cleaner cut through it very well. Made a easy job of what was otherwise a real mess. Don't know if you have ever experienced this, but on some old vehicles that have been sitting the rubber components on brake calipers (boots, seals, etc) will also dissolve from old contaminated brake fluid. It creates the same sticky thick tar and even brake cleaner won't get it off. But carb cleaner will. So I wonder if a gallon can of Berrymans carb dip poured into the gas tank will wash this goo out?

 

[lookforjoe]

Today I began the phosphoric cleaning of the tank. The acid that was readily available at my local builders supply (inexpensively) is a pre-diluted solution (40%). At this dilution you could use it full strength as packaged. However the X's tank is about 13 gals, so it would get a bit expensive to do that. Instead I used 2 gals acid and 3 gals hot water. That means I will have to do one end of the tank, then flip it on one side, then the other side, and finally the other end. Furthermore at this dilution it will have to sit overnight to clean a tank as bad as this one. So about a 4 day process. Not for the impatient I agree, but it is the most effective method and will save this tank. I'm the type that would rather spend the time and a few dollars this way than spend a lot of money for a new tank (which I've read has its own issues).

To do the phosphoric cleaning process:
1) Clean as much unwanted material out as possible with plenty of rinsing, physical agitation (eg. shake the tank around with a piece of chain inside if it is that bad), and a degreaser rinse to eliminate any oily coatings (dramatically slows the acids effectiveness).
2) Plug all openings with whatever it takes. Here is what I had on hand; some plastic/vinyl hose caps/plugs (red arrows), a piece of old rubber inner tube with a hose clamp (blue arrow), and a plumbing temporary plug (yellow arrow). The plumbing plug is nice because you can take it in and out easily.

View attachment 14638

3) Prop up the tank to whatever position you wish to clean. In the above photo it will clean the bottom third or so. With one plug removed (yellow arrow), add the hot (adding heat energy will help the chemical reaction) water to the tank first, then using a funnel pour the acid in second. Keep the garden hose on hand to rinse any spillage and wear appropriate safety gear.
4) Secure the removed plug and shake the tank around to help mix the solution. Then loosen one of the plugs at the top (yellow arrow one in this case) to allow it to vent. Otherwise it will build pressure as the chemical reactions take place and may blow off one of the plugs.
5) Let it sit, in this case overnight. The length of time required will depend on how bad the tank is, what percent of acid solution you have, and the temperature. Occasionally shake the tank around to agitate and keep the solution mixed.
6) Tighten the loosened plug at the top and turn the tank to a new position to clean another portion of it. Loosen another plug to allow venting again. Repeat this until all areas inside are cleaned. The inside surfaces will get a grey color to them when they are clean. This is the phosphate coating that is left from the phosphoric acid's reaction and provides a great protective coating from future rust, etc. Other acids will not do this and that is the main reason for using phosphoric acid. Plus it is a safer acid to work with than most others.
7) Drain the solution from the tank. Save it because it can be reused several times for all types of cleaning and metal prep. Then rinse the tank using some water mixed with baking soda to neutralize it. Here is where the remaining phosphate coating is great, because without it any rinse with water would immediately start new rust formation on the fresh bare metal. Dry the inside thoroughly and it is ready to be put back in the car.

As you can tell from the description of the process, it should be done with the tank out of the vehicle. It is a bit physical (a tank with liquid inside is a little heavy) and takes time for the acid to work. But the general prep and overall process is not difficult.
I'll try to get a picture of the inside when it is done. But I won't risk getting my medical borescope dirty so I might not be able to show much.

Many thanks for the detailed description! I just removed the gas tank from my parts car, and clean as it looks,I'm goign to treat & store it for future use. I'm looking locally, and see Kleen Strip Phosphoric Prep & Etch. It doesn't say what the concentration is though - but looking around it is in the 35-45% range, so I'm assuming I can follow your steps.

 

[dllubin]

I'm not convinced this goo is from fuel varnish. It seems more like a growth or organic byproduct of some type. So it may require a different approach than most tank cleanings. I wondered if good old bleach might kill it?

I'll be curious to hear what you find with those 'Oxi' products. I've used oxalic acid ("wood bleach") to clean out really bad radiators and cooling systems (block, etc). It strips away all of the heavy build up that clogs things up. It has a somewhat similar chemical property as sodium percarbonate (mostly concentrates of hydrogens and oxygens). Not sure how it would work here.

The phosphoric acid seems to have removed this goo stuff from my tank. But it was slower than cleaning a tank that is just rusty. As I noted, it appeared to loosen the goo and put it in suspension in the acid mixture, rather than completely dissolve it. So the goo washed out with the acid. But it also pretty much ruined the acid from future use for anything else (cross contamination).

When I cleaned the other tank (non-Fiat) with the "tar" in it (from dissolved rubber/plastic components), I found carb cleaner cut through it very well. Made a easy job of what was otherwise a real mess. Don't know if you have ever experienced this, but on some old vehicles that have been sitting the rubber components on brake calipers (boots, seals, etc) will also dissolve from old contaminated brake fluid. It creates the same sticky thick tar and even brake cleaner won't get it off. But carb cleaner will. So I wonder if a gallon can of Berrymans carb dip poured into the gas tank will wash this goo out?

I went out and got a big box of OxiClean today. I'll plan to try it out tomorrow. Right now, the tank still has the gasoline I put in yesterday. Today, I got a long, thin pipe and used it to stir up the bottom of the tank. It turned out to be quite effective in loosening everything off the bottom and getting it into suspension. I decided to leave my gasoline stew in the tank overnight to see if it will dissolve anything else in there. Tomorrow, I will empty it out and start on the OxiClean. I have a feeling most of the garbage in there will come out with the gasoline, which turns out not to be too bad a solvent for what is in there.

Speaking of Berrymans, last night during my research, I came across a number of people recommending it for cleaning fuel tanks. I think the specific product was B-12. Could get expensive though. I used a can of Gumout carb cleaner to clean out my new fuel lines that got fouled. It seemed to be quite effective. A number of the tank cleaning discussions I read pertained to motorcycle tanks. The smaller tank sizes make some options more practical than if they were dealing with an automobile tank. However, they seem to have issues with successfully cleaning the inside of the tank without destroying the paint job on the outside. Definitely not an issue for an X1/9.

 

[dllubin]

Many thanks for the detailed description! I just removed the gas tank from my parts car, and clean as it looks,I'm goign to treat & store it for future use. I'm looking locally, and see Kleen Strip Phosphoric Prep & Etch. It doesn't say what the concentration is though - but looking around it is in the 35-45% range, so I'm assuming I can follow your steps.

I saw the Kleen Strip in Home Depot today but decided to see if I could get some information on the concentration before buying it. It says to paint metal within 48 hours to prevent rust so I was wondering if it was too low a concentration to provide any meaningful rust protection.

 

[Dr.Jeff]

see Kleen Strip Phosphoric Prep & Etch. It doesn't say what the concentration is though - but looking around it is in the 35-45% range

I saw the Kleen Strip in Home Depot today

In the past I was able to get regular phosphoric acid (I believe around 80% concentrate) in gallon containers at local stores. But the other day when I went to get more (for the tank cleaning I just did) I only found the same as you guys - "Prep and Etch" (although I only looked at one store). I've used this product before for pre-paint prep of bare metal. It is a 40% solution (the old label used to say that on it). I went ahead and bought a couple gallons. By the time I added a couple gallons of water to help fill more of the tank, it was pretty weak. I had to let it sit in each position for 24 hours. A stronger concentration will do the same in a couple hours. So it's slow but it will work. As mentioned, with a car tank (vs a bike's) the volume is large and it takes a lot of fluid to cover much. If you find ways to plug the holes well enough, and calculate how much area inside the fluid covers, then you can plan a method of placing the tank in a position to do one wall at a time and turn it again and again to new positions. That way you can use less fluid (I recommend the straight 40% Prep and Etch acid without diluting it).

 

[lookforjoe]

In the past I was able to get regular phosphoric acid (I believe around 80% concentrate) in gallon containers at local stores. But the other day when I went to get more (for the tank cleaning I just did) I only found the same as you guys - "Prep and Etch" (although I only looked at one store). I've used this product before for pre-paint prep of bare metal. It is a 40% solution (the old label used to say that on it). I went ahead and bought a couple gallons. By the time I added a couple gallons of water to help fill more of the tank, it was pretty weak. I had to let it sit in each position for 24 hours. A stronger concentration will do the same in a couple hours. So it's slow but it will work. As mentioned, with a car tank (vs a bike's) the volume is large and it takes a lot of fluid to cover much. If you find ways to plug the holes well enough, and calculate how much area inside the fluid covers, then you can plan a method of placing the tank in a position to do one wall at a time and turn it again and again to new positions. That way you can use less fluid (I recommend the straight 40% Prep and Etch acid without diluting it).

That's what I had in mind - buy two gallons & keep rotating the tank to allow a wash to cover a surface plane. I would expect 2 gallons is sufficient to submerge each of the largest planes in a film of acid if done that way, even heavy "liquids" such as 2 part epoxy resins are good for 48sq. ft. surface area per gallon coverage, for example. The largest flats are not that great, not even 16sq.ft. I'd reckon - I didn't measure it though. The only reason it wouldn't work that way is if the acid needs a certain depth over any given surface for it's properties to operate?

 

[Dr.Jeff]

The 'depth' really isn't too critical. Technically the ratio of liquid to surface area covered does effect the dilution strength at any given point due to the availability of sufficient acid for the chemical reaction to take place. But in this case with a 40% solution (full strength Prep and Etch) and the quantities/surface areas we are dealing with it won't be an issue. Depending on the condition of your tank, it will need to sit in each position for several hours (perhaps as much as 24 hours). So if the area covered by the solution is fairly small it will be a long process to get everything covered (that time period for each of the numerous tank positions).

 

[dllubin]

I poured the gasoline out of my tank today. It seemed to have loosened the tar at the bottom of the tank enough that it would slowly flow. I turned the tank upside down over a pan for about an hour and got most of it out. I then put in 5 scoops of Oxi Clean into the tank and filled it right up to the sender hole with hot water. I plan to give it about 24 hours and see what it looks like. The concentration I used was perhaps a bit on the light side but the time and temperature should help a bit. If I end up needing a real high concentration, I'll go to the tank flipping trick to conserve the cleaning solution. When I first got the tank loaded up, there were quite a few bubbles coming out of the orifices so some kind of reaction was going on. The instructions say that for real tough cleaning, you can add a small amount of water and use it as a paste.

UPDATE: After about 5 hours of Oxi Clean in the tank, I stuck in the pole that I had been using to stir things up with the gasoline. I noticed a big difference in the feel and sound of the aluminum pole sliding on the tank interior. Where as earlier you could sink the pole into the tank and feel the debris, and not really hear a sound, now the pole slides along the interior and it sounds like a steel drum. There must be some serious cleaning going on in there. I'll have a look tomorrow.

 

[Dr.Jeff]

For anyone that uses the 40% "Prep and Etch" phosphoric acid to clean a tank. This was my first experience using a dilution concentration of this (low) level so I've found a couple things to help with it.

It will work great, but that concentration is about the lowest level of acid that should be used. As mentioned earlier I diluted it more to get greater coverage. But I've found it to be too weak. Not only does it require a LOT more "soak" time to get a thorough cleaning. But it does not 'etch' the tank's interior walls as well as I would like. When the acid reaches the metal wall (after eating through whatever contamination is covering it), it creates a chemical reaction with the metal. That is where the protective phosphate coating is developed, from that reaction. So the weaker acid only causes a lesser level of reaction and makes a thinner phosphate layer. In places it is not sufficient to adequately protect the bare metal surface from reacting with the rinse water, and a light flash rust can form in spots. This was with a solution diluted to about 25%. A stronger concentration will work better; not only with the cleaning (removal of contamination) but with the protection (phosphate coating).

Two options:
1) If you can find a concentration of phosphoric acid around 50% to 60% it will work best. The time required will be less. And rinsing with water will be no problem.
2) If you use the 40% concentration it will work well but do the following; a) do not dilute it further before using it, and b) consider rinsing with a non-water based agent (paint thinner or even gasoline for example) to help avoid any possibility of flash rust from forming. This level of concentration is low enough that the rinse process is not as critical, so it does not require a lot of rinsing. How contaminated your tank was to begin with may be a factor; really heavy contamination will leave a really dirty acid solution after soaking, and a little more rinsing is needed to get all of the loose material out.
If you choose to dilute the acid further or find a product with a concentration lower than 40%, then it won't work as well. Be prepared to have a very long soak time (as much as 48 hours per position if the tank is bad) and definitely do not use any water based products afterwards.

The level of results obtained is determined by several factors. How bad the tank is. What concentration of acid solution you use. The prep process that is done prior to the acid wash. The length of time allowed for the acid to work. Even things like the temperature (heat affects chemical reaction rates), humidity, etc can play a role.

 

[dllubin]

For anyone that uses the 40% "Prep and Etch" phosphoric acid to clean a tank. This was my first experience using a dilution concentration of this (low) level so I've found a couple things to help with it.

It will work great, but that concentration is about the lowest level of acid that should be used. As mentioned earlier I diluted it more to get greater coverage. But I've found it to be too weak. Not only does it require a LOT more "soak" time to get a thorough cleaning. But it does not 'etch' the tank's interior walls as well as I would like. When the acid reaches the metal wall (after eating through whatever contamination is covering it), it creates a chemical reaction with the metal. That is where the protective phosphate coating is developed, from that reaction. So the weaker acid only causes a lesser level of reaction and makes a thinner phosphate layer. In places it is not sufficient to adequately protect the bare metal surface from reacting with the rinse water, and a light flash rust can form in spots. This was with a solution diluted to about 25%. A stronger concentration will work better; not only with the cleaning (removal of contamination) but with the protection (phosphate coating).

Two options:
1) If you can find a concentration of phosphoric acid around 50% to 60% it will work best. The time required will be less. And rinsing with water will be no problem.
2) If you use the 40% concentration it will work well but do the following; a) do not dilute it further before using it, and b) consider rinsing with a non-water based agent (paint thinner or even gasoline for example) to help avoid any possibility of flash rust from forming. This level of concentration is low enough that the rinse process is not as critical, so it does not require a lot of rinsing. How contaminated your tank was to begin with may be a factor; really heavy contamination will leave a really dirty acid solution after soaking, and a little more rinsing is needed to get all of the loose material out.
If you choose to dilute the acid further or find a product with a concentration lower than 40%, then it won't work as well. Be prepared to have a very long soak time (as much as 48 hours per position if the tank is bad) and definitely do not use any water based products afterwards.

The level of results obtained is determined by several factors. How bad the tank is. What concentration of acid solution you use. The prep process that is done prior to the acid wash. The length of time allowed for the acid to work. Even things like the temperature (heat affects chemical reaction rates), humidity, etc can play a role.

That might be why the instructions say to paint the bare metal after etching. I looked on line and 75% phosphoric acid seems to run about $50/gallon.

 

[dllubin]

I emptied my tank full of Oxi Clean. The results were impressive, especially considering I was running half strength (1/2 scoop per gallon). About 80% of the tank is down to bare metal. Better yet, I have found no rust in the tank. What looked like rust was varnish. I think the combination of gasoline varnish and tar actually preserved my tank. I shot up the inside with a pressure washer and found quite a bit more loose chunks of varnish came off. There were pieces coming off the bottom close to an inch thick. One of them had a decent sized piece of that aluminized firewall insulation sticking out of it. I guess somebody accidentally dropped it in the tank on the assembly line. Right now I've got a 10 scoop, ~5 gallon solution in the tank (double strength) with it laying on its side. I plan to flip it after a few hours and soak the other side. I'm sure the tank is good enough to use now but I am compelled to get it spotless for some reason. At this point I probably won't be using the phosphoric acid since I have not found any rust. The nice thing about Oxi Clean is that it is cheap, biodegradable, and it actually works. If you don't want to do any flipping, it is cheap enough to fill the tank. I did that yesterday and if you get the angle right, you can fill it up so that everything except the last inch or so of the filler is covered without using plugs.

Here is a photo:

The stuff left easily comes off with a pressure washer. What would be nice for this would be a 90 degree rotating pressure washer head.

 

[dllubin]

I decided to fill the tank a third time with the full strength solution and let it sit a couple of days. This softened up the remaining deposits to the point where a fan spray pressure washer nozzle or even a strong hose nozzle was able to remove them. Time to paint the outside and stick it back in the car.

 

[Dr.Jeff]

I was wondering how you came out with it. Hope that's the end of the fuel contamination for you.

On mine the acid wash removed all of the crud and left it quite clean. I will say it was different than any I've dealt with before though. Initially the gunk was hard in the tank until the acid attacked it. Then it became soft, broken down to a gel like substance, and suspended in the acid solution - looking like something from a alien movie. It poured out still suspended in the acid solution. But once the solution was allowed to sit still for awhile (in old containers), some of the gunk would separate again. Very sticky and viscous. I wonder if Fiat coated the tanks with something that broke down over time, creating this stuff. I've restored several old tanks and never come across this before.

 

[dllubin]

I was wondering how you came out with it. Hope that's the end of the fuel contamination for you.

On mine the acid wash removed all of the crud and left it quite clean. I will say it was different than any I've dealt with before though. Initially the gunk was hard in the tank until the acid attacked it. Then it became soft, broken down to a gel like substance, and suspended in the acid solution - looking like something from a alien movie. It poured out still suspended in the acid solution. But once the solution was allowed to sit still for awhile (in old containers), some of the gunk would separate again. Very sticky and viscous. I wonder if Fiat coated the tanks with something that broke down over time, creating this stuff. I've restored several old tanks and never come across this before.

I had a similar experience with the gasoline that you had with the acid except that it took a week+ to get the hard stuff on the bottom. Now that the Oxi Clean has it down to bare metal, I was wondering why the steel inside will not rust, even with water droplets sitting inside. I would not be surprised if there is some kind of surface treatment.

 

[Dr.Jeff]

Did you use anything to remove all traces of water, or are there actual droplets of water still inside? If there is water, then give it a day or two and see if there is still no rust. If the cleaner actually got it down to bare metal it will rust. But if there was some sort of factory coating and the cleaner got down to it (and not through the coating), then it won't rust.

When I look inside mine there are areas on some surfaces with a slightly different color. At first I thought it was due to the weaker dilution of acid I used, not allowing a good phosphate coating to form everywhere. But even after a second acid treatment there are a couple of small areas like that. I'm wondering if originally there was a protective coating that broke down over time.

By comparison. On my '79 carb tank there was no rust or contamination at all. But that tank spent its life in SoCal. The '85 FI tank that had all the crud spent its like life in a snowy wet area. When I look inside the '79 tank, the color of the inner walls appear to be a bit different color than most metal tanks. So it may be that Fiat did coat the tanks and the one that lived in a dry climate is still protected. While the tank that lived in a harsh climate lost its protection and allowed all the problems to form. I'm just speculating though.

 

[dllubin]

The outside of the tank may also have a coating. When I took off the insulation pad from the front of the tank, there was mostly shiney bare metal underneath. Not sure why the paint was absent except where the indents in the steel were. The paint stuck fine to the rest of the tank. Anyway, that bare exterior had standing water on it for a couple of days and no reaction - pretty much like the inside. I've got some light surface rust where there were a few scratches and also where the steel bands rubbed off the paint on the bottom. I plan to paint the outside tomorrow and get the tank back in.

My tank has led a relatively benign life in the Bay Area. It has also spent almost all of its life under cover. The worst thing that happened to that tank was having some gas sit in it for 23 years. Glad I managed to siphon out most of it in 1995.

 

[Dr.Jeff]

My '85 tank also has a very thick coating on the lower half only. It is like undercoating and is clearly from the factory, but it is different from the rest of the car's undercoat.The top half is just black paint. And like yours there are places where it has been disturbed and has rusted.

 

[dllubin]

My '85 tank also has a very thick coating on the lower half only. It is like undercoating and is clearly from the factory, but it is different from the rest of the car's undercoat.The top half is just black paint. And like yours there are places where it has been disturbed and has rusted.

The lower part of my tank has a bit of undercoating on it but it looks like it was from when I had the car undercoated when it was new. In this climate, it was probably more useful as sound deadening. The car was noticably quieter as far as road noise goes after it was undercoated. When I do my touch-up painting, I need to decide whether or not to remove it, paint over it or paint around it. Since it is providing protection and is not easily visible, I am tempted to paint over or around it. Also, not that easy to remove. I had a few bottom covers that had some on undercoating on them and I used a big wire wheel on my radial arm saw to get it off. The wheel makes short work of rust but can get a bit messy when removing undercoating.