So, my 86 XT has eaten two fuel pumps now, and quite a few fuel filters because of vanish still sitting in the tank.  The tank doesn't appear to be rusty in any way, which is great, but the poor thing had been parked for 10-13 years, with about a 1/8th of a tank of gas, which I can only assume has turned into a thick layer of gunk on the bottom of the tank. I did drain out that gas and tried to flush out all the old stuff but that clearly didn't do the trick. I've seen a million recommendations online about cleaning varnish out of a tank but what have people here had the most success with? Should I just throw some fuel treatment or seaform or something and let it sit for a couple of days, or should I just take the whole tank out and get shaking it with vinegar and rocks? I would hate to take the tank out, only because I know how annoying it can be, but I guess it would be just as annoying to keep buying fuel filters 😆.

I’d say the most effective way would be tank out and clean with whatever method of choice.

You could source a good, clean tank, put that in and be done with it too. 

Whenever a severe fuel tank issue comes up i offer that I sent mine Moyer in PA

They have their own non epoxy patented formula they use after completely removing all rust snd they’ll do any repairs as needed. 
 

Mine was from a 79 4wd wagon same tank as a Brat. It cost $500 total with shipping. The tank looks bulletproof and should last through my kids lives. 
 

Ok $500 isn’t for everyone so use one of the many methods. But from what you’ve described it seems severe to me. 
 

Folks have done motorcycle tanks in cement mixers with the tank wrapped in moving blankets. Think up your own method or research. Lots of folks have used nuts n bolts and cover the holes - after adding some solution like gasoline, swish it around but with a car tank thats quite the chore. So maybe something similar to the cement mixer method. 
 

I own a condo and it was better for me to open the wallet. 
Good luck. 
 

pardon any typos, phone is being unkind. 
 

Moyer: http://www.gas-tank.com

Unsecure site it says but they’re fine and you can bet if you do business with them it’ll be secure.

Nice people on the phone too. 

 

To those wondering about tank treatment and fuel compatibility Moyer claims theirs is good for all contemporary fuels. 
 

I used my tank for a little over a year then removed it because the new owner is making the wagon electric. So I kept that tank and it looks like the day I got it back on the inside, and out. 
 

Enjoy ! 

Last time I had a dirty tank that kept clogging stuff...   I put in the largest filter I could find before the pump, and changed it as needed until the problem went away.

I'm on the west coast, so sending my tank to those guys in PA might be a bit difficult for me, but I will definitely keep it in mind. The fuel filter right before the pump is a good idea, I don't know why I didn't think of that sooner! It would at least help keep it from eating my pumps lol. I'm kinda having to drive the thing regularly to get to work right now since my wagon is undergoing some of her own repairs. So as soon as she's done, I think I'll take out the tank and just, scrub away what I can and then give it a good so soak in some vinegar, and follow up with baking soda since that seems to work with other people. Hopefully just running it and changing out filters will clear up some gunk, and the bath will get the rest. I'll follow up with results!

Lol took me a bit to get around to this, but also, I've been taking time to try and get this thing cleaned up. I was "encouraged" by the car itself to start actually working on this thing, since it actually died on a test drive around my neighborhood.

The short version of what I did: I cleaned out the tank with water and let it soak in vinegar for a few days, then washed rinsed it out with gas to get as much of the vinegar out as I could. This seemed to clean things up but is also loosened up flakes of rust and varnish, which, after putting the tank back in the car and running it clogged up the lines in the tank, but didn't luckily get into the engine as far as I can tell. I took the tank back out of the car again, and setup an old pump with a filter to a power supply and used it like a mini-vacuum cleaner, taking one end of a line and picking up chunks of gunk. This worked pretty well, and got most of the big chunks out, however gas still seems to struggle coming out of the tank, which is where my questions begin for you wise techs out there.

The first thing I notice is that, with my pump bench setup, when the pump is running, there seems to be a bunch of air bubbles viewable in the filter. This seems unusual because when pumping gas directly from a can, I don't see these bubbles at all, at least, very little of them. It does this while the tank is in the car as well. Here is a video of what I mean: https://youtube.com/shorts/H7jIOtXonMo?feature=share In this setup, gas is coming out of the outlet and then right back into the return line.

According to the manual, there is an internal filter inside the tank, and I am thinking that that filter may be clogged up with gunk still and that is why the pump struggles to get anything out of the tank, but I dunno about those bubbles in the gas... If anyone has any wisdom that would be much appreciated.

Also, I am totally on board with getting a new tank rather than stuggling (and failing) to clean or fix this one. This tank has two pinholes at the top of tank already, so I know it's not worth keeping. I just wanna try and get it flowing, so I can at least have fun driving it around town. I may hopefully be able to get a tank I found from someone on facebook, but we'll see. Who knew that trying to source a gas tank for a 40 year old car would be so hard! 😁