During the latest round of EFI issues with my 77, with some help from @Patcon we isolated the fuel delivery problem to the fuel tank. I had cleaned and treated the tank for rust a few years ago. But that apparently didn't work. After dropping the tank I got a few cell phone photos of the inside for confirmation. Lots of rust. We suspected the primary issue is a rusted through pickup tube.

Fast forward to yesterday. I took it to a buddy who is a master with a cutoff wheel so he could help me cut it open.

We cut just inside the factory weld on the flange, leaving plenty of material to weld it back together later. After getting it open, it's clear that I did the right thing. Everything is rusty. Even the brass screen inside the fuel baffle is corroded. I'm posting pics for anyone who wonders what these look like inside.

Bottom half from passenger side:

Bottom half from driver side:

Top half:

Borescope photo of screen:

The plan is to bead blast this clean and thoroughly coat it, leaving a strip for welding. Then I'll slosh more coating over the completed weld seam. More to come.

Now for some questions. 

What's the small tube sticking up out of the screen for? It's open at the end, and doesn't connect to anything.

What's your favorite coating? In my case, I'll need something that can be brushed on, and later thinned enough to slosh inside the seam. So it has to be able to stick to itself as well as it sticks to steel.

What's the easiest way to remove the old tar-based undercoating from the outside of the tank? I'm thinking propane torch and a spatula. Is there a better way?

Edited December 24, 20231 yr by the_tool_man

Post a picture of down in the well where the little tube connects and the venturi

 

• • r
•  

 

 

 

Edited December 24, 20231 yr by mayolives

I've used the POR 15 tank treatment two times. Worked well for me and both cars are running strong after at least 5 or 6 years.  What treatment did you use? Doesn't look like it did much to protect your tank!

Edited December 25, 20231 yr by mayolives

One of the aspects for coating the tank are the complexities of the inside of the EFI tank. Inside the tall tank baffle is a small cylinder with a brass screen. It also has that thin line coming up towards the top of the tank.

I think John is thinking of coating the inside of the two halves of the tank with a brush to deal with all the complexities that probably won't coat all the way by sloshing sealant around.

That means what ever you use needs to adhere to the cured coating once the halves are rewelded and the belt area needs to be sealed as the last step.

How does the sealant effect the brass screen?

I think a tank sealant would plug the screen. It's quite fine. I plan to leave it uncoated. I may remove it, since I've installed an external filter before the pump.

I would remove it. The external filter will take care of that. It's finer and more importantly accessible!

The sealants I have used might even stop up the little line

I haven't updated in a while. But I've been researching chelating chemistry for de-rusting the tank instead of more destructive methods like acid or bead blasting. When Evap-O-Rust was $12/gallon, I wouldn't have balked at the cost. But now it's $30/gallon. I found some info on using EDTA mixed with citric acid to form a DIY, pH neutral chelating agent. Here's one guy who made an instructional video:

He claims $0.75/gallon, but the cost of EDTA has skyrocketed in the last few years, driving the cost of a DIY chemical to about $15/gallon. Then I found something called Rust911, which is a concentrated chelating chemical you just add to water. One $75 gallon makes 16 gallons. That's what I'm using.

With that sorted, I needed to strip off the rubberized undercoating on the bottom half of the tank. I ended up using a propane torch to soften it so I could scrape it off with a narrow spatula. It was tricky, because too little heat and it wouldn't budge, but too much and it would smear around. And if I let too much collect into a glob, it would catch fire. It became a balancing act to move the flame around with one hand while scraping with the other.

Here's what I started with:

After scraping off what I could:

There was still a lot of coating in the concave areas, so i followed up with more heat and a wire brush:

It took some paint off, too. But I plan to strip and repaint most of the outside anyway. I ran out of propane at this point. Overall, while it was a nasty process, it worked pretty well. I only burned one of my fingers. And what's left on the tank should come off with stripper, or if I use the bead blaster. I pity the person who tackles removing this undercoating from the body. I have no plans to do it. Next, I'll set up for de-rusting the inside. Stay tuned.

Edited February 5, 20241 yr by the_tool_man

The (car) world would have been a better place if tar-based rustproofing had never been invented!