Best way to clean a fuel tank ?

Hi, I am new to the site, but have read alot of the postings.
I have a 86 xj7oo with 2100 miles on it. It was driven then stored for 20 years + From what I was told the tank was full when it was stored. But now it has been reduced to a green 1/8 thick hard coating on the bottom of the tank. The paint on the tank is "new" - what would I use to clean out the tank?

 

As long as it's not rusted internally, the best thing to dissolve the old dried out gasoline with would be new fresh gasoline. (Which you would then dump out.)

If it's lightly-to-moderately rusted inside, then I recommend a phosphoric acid flush before going to something more drastic like electrolysis.

 

You say the paint is "new".. how long has it been since painting, and what kind of paint was used?

Many of the "good" ways to clean out a rusty and varnished tank are not good for paint- especially fresh paint. It will require extreme care.

For "most" tanks.... I like to use a solution of drain cleaner crystals (NaOH- sodium hydroxide), VERY HOT water, and a length of chain. You can adjust the strength depending on how bad the inside of the tank is. Just mix up the solution, pour it in, add the chain, and shake and tumble it inside the tank. Most will notice it is rustiest on the TOP of the tank. Repeat a few times. Rinse thoroughly, then pour in a few ounces of 2-cycle oil. Shake that around and pour off the excess. This will keep the tank from rusting until you can start using it.

I try to stay away from the drain cleaners with Hydrochloric Acid in them.

If you REALLY can't get any solution on the paint, you will have to tape and cover the tank as best you can.

 

A pack (25 or so) of #10 external star lock washers and a half can of Seafoam will eat up the rust and varnish if shaken around for awhile, maybe a long while in your case. I removed the petcock and sender unit and blocked off the 2 holes. I rinsed it out with mineral spirits a few times as it's way cheaper than Seafoam for rinsing.

 

Thanks for your help – What I was referring to as the paint is “new “ is the paint is factory –but does not have a scratch on it. It took me over two hours to get the gas cap off. But to my surprise there was no rust. The fuel sender is toast and the petcock is a goner as well. ( stuffed with crystallized fuel ) I took a long screwdriver down into the tank and the crystallized fuel would flake off – I am attempting to clean the tank without damaging the paint on the tank – I was unsure of using harsh chemicals yet. But I do like the idea of using some chain and some cleaner. – Can’t wait to ride ---- Imagine this ---- I got the carbs cleaned, back on the bike and tuned. Told the wife “ check the cookie jar – you may need bail money “ Took the bike out, twenty year old plates and a test tank strapped to the frame ! My hearing is next Tuesday – not really –I live on a country back road – the bike ran sweet !!

 

Stick your finger inside the tank as far as you can and check the TOP of the tank- That is where most rust-flakes show up. You don't really get much in the bottom unless water has been condensing inside and left to sit a loooooong time...

Ray

 

Thanks for your help, I looked at the tank again last night. I could not stick my finger into the tank, there is a lip about 1 ½ inch deep . But I took a small mirror and a flash light. You are correct there was rust on the top side of the tank. It was smooth and even, not flakey. About 2 inches down from the top of the tank, there is a blurred line going from rust to green varnish. From what I can see, the varnish is dry, powder like and scrapes off easy with dull gray steel underneath. The bottom inch of the tank has the heaver crystallized varnish. I could only see about half of the tank – The fill hole is offset to the right of center.