I wanted to provide closure (and a victory lap).
The first time I noticed problem, there were 3 bars on the fuel gauge, and car stopped. a gallon of fuel donation made it go. So whenever the gauge got to 3 bars, it would get stuck there, and would get just 17 gallons of fuel to full. Then I removed the spare tire and the panel behind, and saw the top of the tank collapsed… I drove with it for over 4 years (I know, shame, shame…)
I got replacement fuel tank at Pick-and-Pull for about $40. The tank was a bit rusty and white-salted (that’s oxide of zink, telling you the protective coating on the steel is going away in bulk). I washed the inside of the the replacement tank, sanded the outside thoroughly to steel-shiny, the painted several coats of Rust Oleum titanium silver primer & paint. The photos show the results. I should have left the tank outside for one or two more days so paint does not smell in the cabin…
Coillapsed tank in the car:
Tp of the collapsed tank, out of the car:
Replacement tank, as obtained:
So this is what the top of the tank is supposed to look like:
Replacement tank - painted, ready to install:
Replacement tank, installed:
This is glorious - My fuel indicator was at one bar, and I went to a gas station, and got 22.5 gallons in! Now I am still driving with fuel cap loose, until I clean and replace vapor recovery system (charcoal cannister and related valves), which is probably at fault for collapsing the tank. Advice on diagnosing that would be greatly appreciated!