Gas tank cleaning and sealing

[Conaway2]

I last cleaned and sealed a Model A gas tank 35 years ago and have had no problems since. I used the Eastwood products that were available at that time.

I’m now ready to clean and seal the tank on a 1929 Sport Coupe I’m working on, and there are many more products available today. Paul Shinn has also released a video showing use of lead air gun pellets in kerosene as a way to clean loose rust from a tank.

I don‘t think the products I used 35 years ago are still available, so am trying to decide how to proceed on my current project.

The gas tank is out of the car and has light to moderate rust on the bottom - no pinholes that I can see.

I would be very interested in hearing about products that have worked well to clean a Model A gas tank.

Many thanks -
Jim

[Brentwood Bob]

Rust 911 has worked, don't know about sealants.

[Oldbluoval]

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[rotorwrench]

Sealers won't stick to rust. The corrosion has to be completely removed without creating pin holes there the corrosion is worst. Any and all debris and old hardened gasoline varnish crust has to be removed first. The metal on Ford tanks is close to 1/16" thick but I've seen more than one tank corroded all the way through in multiple spots. Acid based rust removers work but sometimes work too well, The 30/31 tanks have a complicated baffle set up in there that is near impossible to inspect around. I have a bore scope that I use to look into tanks but I can't see every square inch in there. The tank etch or prep is still available and is a phosphoric acid based liquid that not only removes rust but also converts the metal to decrease the chance of flash corrosion as the tank is dried prior to using the sealer in there. I've used the Kreem and the Bill Hirsch sealers but have not used some of the later types.

With chemical rust removal, there is always a chance that pin holes will appear after cleaning. Using MEK to dry the tank will tell since it will come out of any pin holes that are there. Tank sealers won't seal pin holes well at all. It's basically just there to prevent further corrosion. The only sure fire way to insure a tank is completely derusted it to cut it open along the original weld seems and then use mild grit blast to removal all corrosion. Weld it back together and then apply sealer. It's not an easy task but then full restoration never is.

There is a modern epoxy marketed as MAX GRE that is supposed to be fuel resistant but I would have to try it before I could say it works. It comes in liquid and gel coating forms. It is used for fiberglass or carbon fiber type tank construction.

[Conaway2]

Thanks for all the comments.

I finally got the filler screen out of the tank and was able to see into the tank under the gas cap opening. There’s some rust, but mostly light surface rust. I’ve got Ospho ordered and will post progress as I try to clean this tank. Not sure what I’ll use for sealing yet.

Thanks - Jim

[BRENT in 10-uh-C]

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Originally Posted by Conaway2

Thanks for all the comments.

I finally got the filler screen out of the tank and was able to see into the tank under the gas cap opening. There’s some rust, but mostly light surface rust. I’ve got Ospho ordered and will post progress as I try to clean this tank. Not sure what I’ll use for sealing yet.

Thanks - Jim

Jim, I can show you picture after picture of tanks that have rust inside. The tank sheetmetal was coated with a Terne finish prior to stamping the tank. What we find is in areas such as corners or radius' where the metal blank was moved in the dies during the stamping process, this rubbing wore into the coating. I have found that the majority of the tank rust always comes from the roof area behind the baffle area. You are wasting your money with the Ospho for two reasons, -one being the Ospho typically causes the iron phosphates to loosen however the loose material generally needs to be removed either with hydraulic pressure (-pressure washer) or mechanically (-rubbed with a cloth or ??). You have no way to access the backside of the baffle areas which the coating will not adhere to loose particles. Second, the Osphos needs to be thoroughly neutralized to remove any of the powdery residue once it has dried. The same method of pressure washing all surfaces, -or wiping all surfaces is generally required to get the metal thoroughly clean. Again, access to these areas is where this becomes a problem.

One final thought on this. It has been my experiences from tanks sent to us that 1 quart of sealer is not enough to ensure that all areas of the tank are properly coated. While the perimeter of the tank walls can be coated while the tank is rotated, generally the back side of the baffle area never receives any coating. As such, the rusting continues in that area. It is my opinion that the only way to ensure the rust has been completely removed is to open the tank, and then use an abrasive media to remove every instance of rust until only bare metal is seen. This metal will now have a slight texture due to the coarseness of the media which allows the urethane sealer to adhere better.

[rotorwrench]

Make sure there is no varnish residue in the bottom of the tank. Metal conditioners won't remove that stuff so corrosion can be trapped underneath. I don't use Ospho in tanks since it has a thickening agent added and is more appropriate for metal parts such as frame work and plate metal where it can be painted over and appearance doesn't have to be perfect since it leaves a bit of a resin like residue. I consider it a primer of sorts unless it is thinned well with water. It may still function OK as a metal prep but I would rinse it well after treatment and then flush it with MEK well before pouring the sealer in. You will want that sealer to stick the best it can. Just to add, I don't know how the metal prep solution will work with a lot of remaining tern plate in there. A person will just have to hope that it has little affect won't detract from the sealing process.

I would use one of three products for a tank. Hirsch gas tank etch, Por 15 Metal Prep, or Eastwood Fast Etch. On a 10 gallon tank is would likely take around a half gallon poured in with a fill up to the top of water to get a good phosphate conversion coating in all the nooks & crannies of a 30/31 tank. The stuff can be reused but 10-gallons worth could be a pain to store. The only way to check progress is to pump or drain the stuff out so that the tank can be checked for complete corrosion conversion. If corrosion is light, it may only take as little as 4 to 6 hours for it to work but is can stay in there longer as long as the metal is still solid. MEK is the best drying agent since most of the sealants use it for a thinner. I know Bill Hirsch's stuff does since I've used it before. Make sure you rinse the tank well with water after completion of the metal prep part. The MEK is the last step in cleaning. If you have any pin holes then that's when you will find them.

One of the big problems is sealing the gas gauge opening and the fuel cap has a vent too. I'd get a large quantity of sealer to do this job since there is so much cross sectional area to cover with all the baffles in there. It takes a while to get a very thick coating on a tank. It takes a lot of patience turning the heavy tank around to distribute it all over in there. A person has to alternate with moving the tank and letting it set to get the coating build up to a good thickness. It can be a pain with a smaller motorcycle tank but they weigh very little compared to a Model A tank. It may be a good idea to recruit a good friend to help with this kind of project and treat them generously.

Brent's photos will give you an idea about how hard it is to get everything coated as well as getting all the corrosion converted. The sealer can be drained and stored for another job but it does take a lot of it to get a complete coating in there. It can be purchased by the gallon.

I've not used the urethane sealer yet so I don't know much about. I've used the Kreem and Bill Hirsch stuff and had good luck with it as long at the tanks are properly prepped and allowed to cure.