Gas Tank Swap

[FiatBen]

Went out to my daily driver '69 the other day to drive to a job. No go. No fuel. Now, that seemed odd but not unreasonable, after all it had some kind of leak for awhile that had me never putting more than half a tank in it because anything more just slowly dribbled out. But this time I had put in about 5 gallons and only got about 30 miles! Not what you'd call your ideal MPG. Since I'm in mechanicking mode anyway, time to deal with it.

Feeling around behind the guard, I could tell the rubber hose portion of the filler was really soft. A quick look at the bottom of the tank showed only a bit of wetness about where it would run from that point. So, a shot of PB Blaster on the two little 8mm nuts holding the guard and let it set because I had no more time that day for playing with my toys.

Pulled the guard. Apparently someone had replaced this hose before because it has ss worm gear clamps instead of the factory original bolted-type clamps (whatever they're called). Sure enough, this hose is a problem.


However, to get it off, you pretty much have to loosen up the whole tank out of the floorboard, all but removing the tank. While crawling around underneath to pull the hose, I see this:


This can't be good....

So, out comes the tank. Having just pulled the tank out of the '82, I noticed this one has much simpler plumbing:


Out comes the tank, and now I can see what I've got to deal with:


I haven't had to time to investigate deeper, but I'm not sure what is rust and what is peeling undercoat. However, when I look inside the hole the sending unit fits in, I can see a bit of surface rust where the drain plug is located.

Can I fix it? Or just replace it? And if I'm going to replace it, can I use the '82 tank I just pulled? And if I use the '82 tank, how do I replumb it back to a simpler arrangement?

[mPedro08]

The difference is becase the '82 would be a FI tank and the other is for a carb with vapor return etc etc.....not sure how tough it is to get one to work instead of the other....must be a decent reason Fiat did not make them the same.

[FiatBen]

Turns out that the layering on the bottom is FIBERGLASS. I 'm guessing this was before POR-15 was widely known. No telling how long ago it was done. There is also a small fiberglass patch in the driver's floorboard that I don't even want to know what's under it.

[redcars]

The FI tank sould not be hard to do. Flaten the ends of the supply and return lines and solder them shut. Now you have a carb tank. Just make sure to vent the tank with a blower while closing of the FI lines. Now you can put in you carb fuel sending unit with the supply and return line. I have a 78 carb and 81&82 FI tanks and that is the only differnce that I see.

[vandor]

What he said, plus plug the 3 vapor lines that are not present on the '69.

[azruss]

If you have a good FI tank, it might be easier to switch with someone with an early tank.

[Danno]

What's under the fiberglass on the tank?

[FiatBen]

What's under the fiberglass on the tank?

Well, started pulling and eventually it all pulled off:


Underneath was a LOT of rust:


So I dug out the drill and wire wheel and started cleaning:


While I could take the cleaning a lot further, this was enough to reveal this problem in three different locations:


So now I'm at the point of decided do I try to salvage it (I hate to throw ANYTHING away) and keep the original tank in the car or replace it. I like the idea of soldering the pinholes, coating the inside, putting a rust preventative/converter on the outside, maybe a layer of rubber/undercoating over that and going on with life. Or, put the '82's tank in it, capping off the extra inlets/outlets is has. The '82 is sludged up and will need some serious cleaning to make it usable again.


Would love to hear from anyone who's been down this road already.

[FiatBen]

Is there a way to cap off these "extra" ports? I really don't care for the idea of smashing them in and soldering the ends. I'd like to think someone could use this tank for an FI in the future even if it goes in the '69 Besides, you can't smash and solder and make it look "factory."

[Danno]

Two things.

1. POR-15 tank kits are f'n amazing, I think you can solder those bits, seal the inside, and paint the outside.
2. One way to easily seal a pair of those ports would be one hose that clamps onto two. For the third port you could put a short length of hose on there and screw a heavy screw into it. It isn't pretty, but it works.

[FiatBen]

In order to use the '82 tank, I have to first clean it out. It's nasty inside:


I've been researching gas tank cleaning and finding lots of potential methods. I am currently leaning toward a good cleaning with muriatic acid (diluted with hot water), but am not sure how to "seal" the metal once it is cleaned back to bare metal. I know I need some kind of etching solution and am considering a second rinse with phosporic acid (Milkstone remover at farm supplies) which supposed chemically bonds and leaves in essence a primered finish.

Of course, I'm still thinking about the old tank. Am taking it to a guy I know today to see if he thinks we can solder it up and be good to go. (He also has a '79 Automatic for sale that I'm going to look at.)

[mPedro08]

I have a tank out of a '71 you can take off my hands...make me an offer. It needs cleaning inside because the fuel got stale but it's in much better shape than either of the ones in your pics.....PM me an email for pics.

[vandor]

Don't even try to use either of those tanks without coating the inside with a sealer. Without that they will never be clean enough to use. Here some radiator shops do that, however some say that the ethanol in the fuel attacks these coatings. I do not know if that is true.

[FiatBen]

Don't even try to use either of those tanks without coating the inside with a sealer. Without that they will never be clean enough to use. Here some radiator shops do that, however some say that the ethanol in the fuel attacks these coatings. I do not know if that is true.

I'd love nothing better than to have a radiator shop boil out the '82 and dip it. However, there are none of those left in this corner of the world. The few radiator businesses here just want to sell/install new radiators. No one fixes anything anymore, which makes the Fiatista a rather singular breed.

[FiatBen]

Anybody had any experience with this:

It is the only thing I have found so far locally. Sold by O'Reillys. Good for up to 10% methanol (which is stronger than the ethanol being added to fuel).