Gas tank derusting, what techniques have worked for you?

May 29, 2006
The 74 Roadster (with Interstate tank coversion) that I bought had been sitting for 20+ years in dry storage but no fuel tank preservatives. What is the best way to remove the surface rust inside permanently? How do you assess if the rust pitting has deeply eaten into the inside of the tank?

I have heard mixed reviews of different tank liner compounds, and I did buy Kreem finally. Yea or nay?
You must get the old gas residue out or the acid will not be effective. I don't like Kreem this is why. They give you a small bottle of MEK to dry it out . The slimy rust is not a good base for this product, Tech phone # was a joke.
Getting the rust out is easy, acid . Now you have put water in and get it back out. Using MEK just don't get it.
Useing POR-15 at this stage you put a hair dryer into the tank the dry thin layer of rust is a good product base. That's what I found.
I just completed my tank with POR-15 and I am pretty happy with how it came out. I haven't ran gas through it yet, but the stuff is rock hard.

I figured I would throw my process on here to help out with any doubts/questions.

So first, of course, I ran the Marine Clean through it for about 30 minutes or so. All I used to seal the tank was duct tape and It leaked alot, but I later fixed that problem. Read on.

I ran the Metal Ready for about an hour and a half, turning the tank every 20 or so minutes (basically followed instructions).

I then rinsed the tank with pretty warm water about 6 times (about a gallon of water each time).

Afterwards, I took a regular fan and taped a plastic bag from the fan to the filler hole of the tank, leaving the back (inlet) of the fan completely unobstructed. I ran that for about 2 days.

After drying, I notice that I didn't get all of the rust out. I then placed ANOTHER order to POR-15, this time for another quart of Metal Ready (rust remover) and A GALLON of Marine Clean (I love this stuff and I plan on using it to remove surface rust and paint from the outside of the tank).

As I said before, I had a lot of leakage from just plain duct tape. So, I cut up an old t-shirt and rolled the fabric into a cylinder shape and twisted it tightly until it was just a bit wider than the petcock holes. Then, I twisted it into the threaded holes until I got it pretty much all the way in. I wanted the fabric to be somewhat difficult to twist into the threads so I would know it sealed well. Then, with about an inch or so of fabric still sticking out of the tank, I slid the finger of an old latex glove over it, being sure to overlap the raised petcock mount and reach the body of the tank. I then wrapped it in duct tape with several smaller pieces rather than one or two long continuous pieces. I spent a good 5 minutes just pressing the tape to insure a good adhesion. Then I repeated the process for the other petcock. **I left these seals on through both the Marine Clean AND the Metal Ready process.***

For the gas cap hole, I took a large piece of fabric and rolled it the same way, making sure that it was very tight. I rolled it to where it was about 1/4" or so wider than the hole when it was wound tight. I then wrapped one half of it in duct tape. I twisted it into the tank fabric side down and went to town.

After running the Marine Clean, rinsing with about 4 gallons of warm water, running the Metal Ready and rinsing with about 6 or 7 gallons of water, I ran compressed air through the tank for about 25 minutes, making sure to get inside each hole and move the flow of air about quite a bit, to get the puddles of water out. I then duct taped a hair dryer to the gas cap hole and ran it on 'Cool' for about 24 hours (most hair dryers run a little warm on 'Cool' setting, which is plenty hot enough). I ran a normal fan against the side of the hair dryer to prevent it from overheating. For the last hour or two, I ran the hair dryer on 'Warm' to expand the metal a bit and get out any last bit of water.

I just taped up the holes when I ran the sealant through it and had no leakage. One thing I found is that it's really hard to get all or the sealant out because the petcocks are slightly raised inside the tank. So, to prevent pooling, I emptied the tank very thoroughly and switched the position of the tank several times for the first few hours of curing. I ran a fan against the entire tank, making sure to get a decent flow through the gas hole, to speed the curing process up a little.

The nice thing about using the t-shirt is that the chemicals will go soak into the fabric and still get to the surface that's covered by it without passing through due to the latex and tape.

So there's how I went about it. Like I said, I haven't ran fuel through it yet, but I could tell it cured well within the first 24 hours. The big thing is drying the metal. 24 hours of drying time with a hair dryer seems about perfect, the fan did the job in about 2 days.
I had good results using the the three step POR15 process when I treated the tank on my T120R about three years ago. The tank had a small fracture underneath. However, about 6 months ago the fracture became larger and the tank leaked. I have had it TIG welded and so far so good. I have not touched inside the tank.

When it came to cleaning the tank on my Norton Commando, which had stood for years with stale fuel in it before I acquired it,I found that Marine Clean was not effective. I tried all types of cleaning solutions-caustic soda, washing soda crystals etc, but none of these worked. I achieved excellent results using a product called CLR[Calcium, Lime, Result] . The product contains Sulfamic Acid, but no phosphates. I diluted the product with water [50%] and the inside of tank cleaned backed to nice shiny metal finish.
Gas tank rust

Just got my commy tank back from Rusteco in long beach CA, they charged about $225 the tank is rust free and best of all they use a bio degradable solution tha wont screw up your paint job.
Thanks to all who have contributed to this thread. I will do a few more internet searches on the specific techniques described here and then take the plunge. I might rig up some kind of jig to attach the tank to and tumble lead shot inside it as a first step before getting involved with chemicals that may affect the paint and require proper disposal.
Michael A. said:
tumble lead shot inside it as a first step before getting involved with chemicals that may affect the paint and require proper disposal.

Will work...but not as well as either throwing a good number of handfulls of smaller nuts and bolts....or buying a length of smaller/medium sized chain at the hardware store and throwing it into the tank with a half quart of heating oil and spending a number of occasions shaking and turning the tank like a mad man on uppers, will.
Nuts and bolts will get to all corners of the inside, and the chain is easy to get out afterwards and works well if both are used simultainiusly. I keep a large can in the shop with just this mixture in it just for the couple of occasions I need this. Hard on the muscles, and the eardrums...and takes a few goes at it ...but works and costs next to nothing...won't ruin a paint job (unless YOU drop the tank...:wink:) and the tank can be rinsed out with gasoline to take the oil and rusty mud out afterwards......

Personally...I see no reason to use any chemical liner in a tank that has had the rust taken out and doesn't leak or have seepage. The rust only needs to come out ...actually...because of the rust getting the filter stopped up, and getting into the carbs to do a stoppage of the jets...other than could sit there and disturb no one. So you have to remove it......but do you have to use a liner? The purpose of a tank liner is to seal the tank...if the tank doesn't leak...why put extra garbage in it?......and if you bother to keep the tank full after going to the trouble of removing the rust....the mere fact that it is full...will insure that rust can not start from anew....

I used liner only one time in a tank....but that tank had sat since 1941 with dried fuel in it and after getting all the crap out of it...there were 12 pin holes in the tank. Now that's a reason to use a chemical liner, and that is just what I did...used the nuts and bolts and chain to clean it, sealed it with Kreem I think, and retained the original paint...after 8 years...still no leaks.