I have a 1985 B250 van that has been sitting for four years. Today I dropped the tank to see why fuel was not getting to the carb. The sending unit and inside of the tank is covered with this stuff that looks like rust, but it rubs off leaveing the metal shiny. The fuel was old and smelled like varnish. The inside of the tank is covered with small ***** (like B.B.'s) of this stuff. What is this stuff and what can I use to dissolve it and get it out of my fuel tank? Thanks.

 

from what I know, this IS varnish, or a crude form thereof. I suspect I have a similar problem but have not yet removed the tank to check.
there were lots of little deposits/formations of this in my carb when I rebuilt it.
I found an article here.. http://www.moparmusclemagazine.com/techarticles/10055/ that says they used muriatic acid. I've also heard that
muriatic is very harsh and that phosphoric acid is better. In searching about this I even read about a guy who uses 5 parts water, one part Molasses to do this! whatever you use, it would probably help to put some dime to quarter sized gravels in with it to help scrape some of this stuff out. Im planning on using liquid parts cleaner and gravel, then lots of dish soap and a pressure washer, or just a water hose. i figured i would dry it out by sitting it in full sun in a black trash bag for a while (with the holes exposed) then run the blower part of my shop vac in it for a while. maybe even some sort of laquer thinner would help, this being largely varnish and all... maybe you could scoop some of this out into jars and see what type of stuff dissolves it best. I hope some of this helps, I guess it all depends on exactly how clean you want to get it.
good luck.
cp

 

Thanks cp0ff for the link to that great article. My tank has those varnish drips that they are talking about. It has a light coat all over the inside. It is now soaking in a mixture of hot water and tide. I will let it soak a couple of days and see what it does. I like the idea of gravel and will try it with different chemicals as suggested. If I can soften this varnish up, I know a guy who will steam clean it for me. My fuel lines are not that bad, but I can,t want to tear into that carb. It's probally a mess. At least I have some Chem-Dip for that job. Thanks for the great ideas. The adventure continues.

 

Try some Coke, it has the same stuff in it....rinse well.....