OT How are steel automative steel gas tank halves joined?
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  1. #1
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    Default OT How are steel automative steel gas tank halves joined?

    I have a fuel tank out of a 2000 Isuzu Trooper. All the tubes and penetrations rusted to nothingness.

    The outside of the tank has minor surface rusting, The inside of the tank is clean and shiny, with no leaks, But the faying surfaces between the two joined halves are spread about 3/8 inch in some areas due to rusting between.

    I need to do some brazing on the fuel tank, so will have the O-A set in hand,
    Can heat be used to clear out the rust prior to refinishing? If the halves are resistance welded, I'm sure any heat would be tolerated. If the halves are BONDED, Heat would be the end.

    Replacement fuel tanks are NOT available for these vehicles, I can't even source fuel pump assemblies to get the tubing parts.
    So I'll do the repairs myself.

    Don't worry all you safety first guys, The tank has been sloshed out with hot sudsy water. You can't even smell fuel with a nose to the fuel pump access hole.

    If you know about fuel tanks, I'm listening.

    TIA

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    I would think they are resistance welded.

    That's a lot of work for a 2000 trooper. Those things are like $300 with the standard equipment slipping GM auto around here or a grand for a stickshift one.

    I was just looking at troopers for a beater hunting rig and went towards Montero since they're the same price, but better all around.

    There is no rust out here. Have you tried any wrecking yards out this way?

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    Trying to repair that is the dumbest thing you could possibly attempt.

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    Did Carparts for the used look, nada. I'm wondering if a wrecker can ship a used tank.

    I've got the Trooper pros on the case.

    Yea, a lot of effort for a cheap rig. But it's real 4WD, and the TOD system is great. I've rebuilt the transmission, and just put new brakes on all four corners.

    It's the only rig I have3 with a HD tow hitch,

    I just spent $40 on steel tubing and rubber hose. That should get it back together again ;-)

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    Quote Originally Posted by kustomizingkid View Post
    Trying to repair that is the dumbest thing you could possibly attempt.
    Is that because it intimidates you?

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    Quote Originally Posted by CalG View Post
    Is that because it intimidates you?
    I agree with kk, from your description, its one rust spot chasing another. Heating will not clean out the rust. In this case you probably will need to cut away all the rust and replace with good metal. A lot of gas tanks were aluminized for corrosion. Don't know how that would affect brazing. For the time and money, be almost cheaper to make a new one.

    Tom

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    Quote Originally Posted by CalG View Post
    Is that because it intimidates you?
    Lol...

    Now I'm no Ross (AlfaGTA) but I am a mechanic, full time, and have been for over a decade. I have also made a good deal of money fixing lots of things that other shops and coworkers have turned away. Up here in MN I have seen all kinds of fun an interesting rust related repairs, and performed many myself. I have welded and plated frames, recreated suspension mounting points, replaced fuel tank mounting straps after they no longer attach to the body and done so many god damn exhaust manifold replacements and bolt extractions that its barely even worth mentioning.

    Of all the shit I have done, never ever would I consider trying to braze a rusty gas tank.... and no I'm not scared, and I'm not unqualified, I just know better.

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    No No, You have it wrong.

    I'm not trying to patch rust through. The brazing is to replace the 1/2 inch steel vent tube in the present brazed in location.
    You know, Heat it up. let the brass flow, pull the old tube, Stick in the fluxed replacement tube and touch the brass rod to it. It's not trying to find good metal.

    The seam around the perimeter is spread, Obviously that area was never more than two pieces of sheet metal close together. close enough to hold moisture and let the rust build. I have had very good results with the A/O torches getting that sort of rust to come free. Often, as the bulk of the corrosion holds moisture, the rapid steam expansion helps break up the flaky rust. This is mostly just to clean things up. It really doesn't need anything to be serviceable.

    You say you have been at it for a decade... I've been spinning wrenches of all sorts farm, auto, aircraft, and industrial since 1965.

    But I don't know how steel gas tank halves in 2000 were put together. I assumed they would be resistance welded. But we all know what "assume" stands for.

    And since these tanks are NLA, I don't want to turn a sows ear into a silk purse.

    Holly will sell me a replacement for $700, but then I would still need to fabricate ALL the parts that presently need repairs.
    Roll over vents, etc.

    ETA

    FWIW This tank is painted on the exterior, looks like some sort of plating on the inside.

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    Quote Originally Posted by CalG
    If the halves are BONDED, Heat would be the end.
    Only tank I've seen here which was bonded, was a concoction made by a local composites guy. Two tanks halves joined together, cut above the continuous weld, with vinyl ester and mat holding it together internally....not going to be happening on any production 4 wheel vehicle I can think of. I'd probably make a tank if it's at a stage of separation at the seam, than try repair.

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    I read what you said.... and this is my final word on the subject and exactly how I would handle the situation.

    Car-Part.com--Used Auto Parts Market

    Look up any part for the vehicle in question and sort by distance.

    Call junkyards in the south, Texas is my go to since shipping is cheap straight up to MN.

    Ship yourself a nice rust free gas tank.

    Treat the new rust free tank with a healthy coating of FluidFilm

    Install tank and move on with your life.

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    Quote Originally Posted by kustomizingkid View Post
    I read what you said.... and this is my final word on the subject and exactly how I would handle the situation.

    Car-Part.com--Used Auto Parts Market

    Look up any part for the vehicle in question and sort by distance.

    Call junkyards in the south, Texas is my go to since shipping is cheap straight up to MN.

    Ship yourself a nice rust free gas tank.

    Treat the new rust free tank with a healthy coating of FluidFilm

    Install tank and move on with your life.
    See post # 4 re Car-parts... BTDT got the reject notice.

    But you can never tell what might turn up some day. by then, I'll have the job done.

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    Quote Originally Posted by CalG View Post
    See post # 4 re Car-parts... BTDT got the reject notice.

    But you can never tell what might turn up some day. by then, I'll have the job done.
    You didn't read what I wrote... almost no yards list gas tanks. Search a different part and call asking about the gas tank. You have to be a little tenacious on a thing like this. But ya know what do I know, I've only been doing this a decade.

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    I have soldered and brazed quite a few fuel tanks. The old ones were terne plate...a lead-tin coating, easy to solder where not rusty. Aluminized steel would be hard or impossible to solder or braze, unless you sanded of the Al first.

    Brazing works often where soldering won't, like on rusty places where the higher temp and active flux can dissolve the rust.

    The problem is that after the repair, you have uncoated, sensitized steel, and a more-noble metal in contact (the braze), and maybe corrosive flux residue also. A great recipe for new rust. IF you can get the area perfectly clean and paint it with some great paint, you can end up with a durable repair.

    It is the rust in your original seam that would worry me. You can't clean it all out. It will keep rusting until it leaks

    In your shoes I think I would make a new tank, out of galvanized steel. If your touch is light, the braze on your seams will run very close to intact zinc coating. Still, very thorough post-fab cleaning is needed...steam (to dissolve flux residue) or light sandblast would be my choice. I'd coat the inside, as well as several coats on the outside and rubber padding under the hanger straps....I think there is a thread somewhere here about gas-tank coatings/sealers

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    Quote Originally Posted by CalG View Post
    See post # 4 re Car-parts... BTDT got the reject notice.

    But you can never tell what might turn up some day. by then, I'll have the job done.

    I searched and see 4 rust-free southern tanks at a yard less than 40 miles from my house. Who would have thunk.

    $45 US apiece.

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    Quote Originally Posted by isaac338 View Post
    I searched and see 4 rust-free southern tanks at a yard less than 40 miles from my house. Who would have thunk.

    $45 US apiece.
    I'll take another look!

    Looks like NS has lots of them, I wonder how they get southern rust free cars up there? ;-)

    I must have set the distance too close when I used the service previously.
    eta. Yup, I had set the search region for "New England" based on a previous search for another car. I didn't reset for a broader search.

    Still nothing near, Phone calls will beat fabrication unless shipping costs are unreasonable. I'll check with a good friend who does body work and gets parts shipped in all the time.

    Thanks for all the good suggestions.

    (I'll still probably end up fixing this one, it's all laid out on the table .....

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    I took a look on car-part.com and saw a bunch of them for less than a C note.

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    The tank halves are resistance welded. Looks like a spot welder with wheels instead of normal tips. The welder pinches and starts to weld and the tank is fed through the rollers. The setup I saw was all robotic. I made a new tank for my Dually, .060 304 ss. I'll never need to do it again.

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    I have an antique automobile with a rusty slab tank that is going to be difficult to repair and expensive to duplicate. I am considering using the existing tank for appearance, and utilizing a plastic fuel cell of the type race cars use. This tank would be mounted inboard behind the seats and would be rust free and easy to clean.

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    Quote Originally Posted by Jim Williams View Post
    I have an antique automobile with a rusty slab tank that is going to be difficult to repair and expensive to duplicate. I am considering using the existing tank for appearance, and utilizing a plastic fuel cell of the type race cars use. This tank would be mounted inboard behind the seats and would be rust free and easy to clean.
    You can have Fuel Safe make a blader to go inside your original tank.

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    FWIW try Loctite "super wick in" around the seam. I recon that it will give you a few more years. Make sure it's dry first.


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