Old coating in gas tank?

T

Thearne3

Member
I have a '31 68B. The tank appears to have been sealed at some time in the past, but rust is starting to come through. No issues with clogs -- yet! Car is off frame for painting and now is the time to do something with the tank - but what to do?

Do any of the cleaning or sealing methods work when there is old coating or does it need to be removed completely first?

Thanks for any advice...
 

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Acetone will soften the latex base stuff. How well it will act to remove it is something I can't relate since I've never tried it. The rust has to be removed completely or converted to iron phosphate with phosphoric acid based chemical or it grows underneath any sealer put in there. Grit blast is the best way but it requires opening the tank at the original seams to do an acceptable job.
 
That appears to be the old Permatex sealer that Hirsch used to distribute. I have never tried the Acetone to see if it would dissolve it, but hot caustic will dissolve about 80% of it. The rest we just abraded away with media since it was 'goo-ey'.

IMHO, the only way to restore that correctly and thoroughly is to open the tank and mediablast everything inside. You likely are going to find when it is opened that there are places that were not covered with that sealer.
 
Cut it open and sand blast it clean. The old coatings won't stand up to the ethanol in the new gas. They will turn into a gooey mess that clogs everything. This is not the cheapest route but one of those pay once cry once moments.
 
Thanks all!

Tank is coming out! Local folks have preferred not to open original seams, but rather cut 3 holes in the back (see pic), bead blast and solder back together. Then use KBS Coatings Tank Sealer (following instructions!)

Any suggestions? Alternatives?
 

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Not on a Model A tank but on a tank for a boat, I have cut three holes for access and then bolted plates over the holes for continued access. I threaded the tank where the machine screws went. I think I used stainless 10-32 machine screws. I used a sealant from Aircraft Spruce. I cannot remember the exact sealant but it was something like https://www.aircraftspruce.com/catalog/pnpages/09-04493.php. The sealant is still holding up after over 10 years and will probably last the life of the boat or over 50 years.
 
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There is Products Research PR1422 and an equivalent from Flame Master Chemseal that are used in wet wing aircraft tanks. The stuff is good but it's expensive and lasts an average of 20 years before the tank starts getting seeps. The old Pro Seal 890 dates back to the late 50s or so. The others I mentioned are newer products but not a lot different. They don't stick to rust any better than other tank sealers. They are available as a thin slosh type material and as putty types so a person has to research them to get exactly what they need. I've yet to try the Max GRE or Caswell epoxy sealers.

I didn't find it too difficult to cut on the seams since I don't cut all the way through. You only have to cut through half way to open the seam. They were resistance welded using the roller type electrodes. Machines similar to what Ford used are still available but a good TIG welder can make the seams look original or at least close. The 1928/29 tanks are a bit more difficult to do but not by a lot. A person can clean and repair them better when they are completely opened up. Those baffles really make it tough to clean 100% of the inside surfaces. There's just too many nooks and crannies in there.
 
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Proseal type sealants will contain pretty much any form of non caustic or non acidic fluid but it will soften with MEK. Ethanol won't even touch the stuff. I've used a lot of chemicals trying to remove the stuff in my career so I've tried a lot of different solvents without much success. Paint removers work faster but they are nasty stuff.

On aluminum & titanium skinned airframes, I used a product called Cee-Bee strip to remove polyurethane and epoxy coatings. Proseal was also used to seal panel seams on the Hughes and MD helicopter types. The Cee-Bee strip would remove most of the coatings but had issued with some epoxy primers like Super Coropon and proseal. That stuff was methylene chloride with acid mixed in. It would burn a person on contact so heavy rubber gloves, safety glasses, and lots of water had to be used during the stripping process. What it didn't remove was scraped off with plastic scrapers and rubbed with MEK soaked rags to get the proseal residue. Not a fun job.

The caveat for using proseal product is the difficulty of removal when it finally starts to seep around rives and screws in wet wings. It is the dirtiest job in the aviation industry.

If the fuel resistant epoxy works well then it may last longer than the proseal products but that is a big unknown until someone uses the stuff to lay up a fiberglass tank to try it out. It will work as a liquid slosh sealer since Caswells has been around quite a while but I've just not used it so I don't know it's limitations.
 
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I had a 1934 Tank that someone had used a tank sealer on. Don’t know exactly what it was. But the stuff had a fairly thick rubberized texture.

I tried acetone & Muratic acid to remove it. Acetone had no effect but the muratic acid seemed to soften it up. But that’s about it.

I cut the tank open and picked and scraped it all out. Media blasting got everything else. Far more work than the tank was worth.
 
The proseal type tank sealers (polysulphide) are more elastomeric or rubber like in nature and are either medium brown or medium gray in color depending on the manufacturer. Methylene Chloride softens them but it's nasty stuff and harder to find in this day and age. MEK fumes will knock you over if you breath them. They make some stuff called Poly Gone 300AG for removal but I haven't tried it yet.
 
rotorwrench,

Just remembering the large quantities of fuel used in The Central Highlands in 1968.

Does JP-4 have the same rusting problems as Av-gas and Mo-Gas or does JP-4 have more "Diesel like" oil in the formulation that reduces rust?
 
JP-4 is mostly what I refer to as white gasoline or wide cut gasoline with a small percentage of high grade kerosene. The civilian Jet A is the other way around with mostly high grade kerosene and a small percentage of white gasoline. I've worked on a few turbine shaft engines that can even run diesel fuel for winter operations. Turbine shaft engines could burn near any type of low viscosity fuel but some are better and some are safer overall so that's what the difference is based on. Military can get away with the lesser cost fuel in JP-4 but I think the Navy only uses JP-5 which is basically similar to civilian Jet-A but it has a higher flash point. JP-5 is a safer fuel to contain on Naval ships so we pay the price for it.

In aviation, we are taught to keep the fuel tanks full. This is for both flight safety and for better fuel system preservation. 100LL avgas is very high quality gasoline that still has tetra ethyl lead in it but the amount has been reduced so it can be used in more general aviation aircraft. The old 80/87 fuel is rarely stocked anywhere in this day and age so operators either have to use 100 Low Lead or use an STC based mix of fuels to lower the octane. Aviation fuels don't have much in the way of oxidizer mixed in like Mogas does. The ethanol is an oxidizer that increases volatility of Mogas but it also absorbs moisture. As is absorbs the more dense mix drops to the bottom of the tank and the little bubbles of that slowly get more acidic and that causes further deterioration of the mix over time. If the vehicle is used regularly then there is not any big problem but if it sets a lot then the fuel goes bad. Higher octane Mogas does last longer but it still has the ethanol so time runs out on it too, Avgas will stay stable for a much longer period of time. Jet fuel can have microbial growth which leaves clot like gel substance rolling around on the bottom so it doesn't last as well as avgas but longer than mogas. When the military puts an aircraft into long term storage (60-days or more), the maintenance crews have to drain the jet fuel out and put light oil in it's place. They bleed the systems with light oil so it fills the system and preserves it. To put it back in service, they drain and filter the light oil into special tanks, then refill and purge with jet fuel. They take it seriously. Most of us hobby DIY guys don't always take things that seriously due to the time involved and the expense of equipment involved.
 
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