Steel Roadster Tank Inside Cleaning

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Sep 18, 2009
My tank sat for a few years and it was about 2/3 full of gas. I forgot to drain it when I took it off the bike.

I noticed a light brownish film inside the tank the other day when I was putting in some gas. The film can be wiped away with a finger.

What is the best stuff I can buy to flush out the inside of the tank? I have already installed an inline gas filter.
Buy a quart of CLR at your nearby WalMart, cut it 50/50 with hot water, and slosh it around in the tank for a while. Let it sit for 1/2 hour on it's bottom, then flip it and let it lay on it's top (on top of some old rags or towels).

Drain, flush, dry with compressed air or shake it out thoroughly then let it sit in the sun for a while.
"Calcium, Lime, and Rust" remover.

In the bathroom and/or kitchen cleaning products section.
I can't see the point of an in line fuel filter, the petrol tap & carb. filters will stop anything.
Yeah, what is CLR?
GP beat me to it! I think the active ingredient is phosphoric acid.

If that brown film is just old fuel residue rather than rust, some fresh gas should work well to dissolve it. "Like dissolves like", right RonL?

Of course you'd want to drain that fuel out and discard it. We're fortunate here to have a Household Hazardous Waste disposal center operated by the county. They accept old gasoline, motor oil, antifreeze, and more.

POR15 makes a product just for this purpose called "Marine Clean" I buy it buy the gallon about 22.00 it can be re-used many times even after it gets funky looking. It is a must for the treatment of a tank before using Phosphoric acid because it will not cut brown sludge left by stale gas. Mix boiling water 50% 50% with the clear dump in drywall screws and shake till you drop rest and repeat about four hours does normally but 48 on bad tanks.
Debby - I burned up the old fuel in my tractor. It will just about run on anything you pour into the tank.

Gp - Thanks. There is a Wall Mart on my way home. I will give the CLR a try.

Thanks to all.
Debby, you remember your Chem 101!! Actually, in the case of varnish from old gas, fresh gas is probably not strong enough to re-dissolve it completely. Lacquer thinner would be more effective. The major problem is you generate all that organic chemical waste. The CLR is mostly an organic acid (lactic) in water and is much more environmentally friendly. It does a fair job on light rust also. In fact, it is designed to dissolve inorganic solids like lime (calcium) and rust (iron oxide).

Marine Clean is kinda the opposite, being mostly potassium hydroxide which is very similar to caustic soda (lye). A strong base like this is quite effective at breaking down organic bonds, so is probably a little more effective than CLR (although I admit I have never used it). Using a phosphoric acid wash after it will neutralize it and passivate the metal. This sounds like a somewhat more effective cleaning procedure.
Flo said:
I can't see the point of an in line fuel filter, the petrol tap & carb. filters will stop anything.

Petcock screen's a pretty coarse filter. I wouldn't rely on it. What "carb filter" are you referring to?

Me, I run quality inline filters and I can't imagine not doing so. But I'm willing to learn! :shock:
I believe the carb filter he's referring to is the screen in the banjo fitting at the float bowl of the Amals.

I had a dirty tank I could not get clean. Fine silt in the carbs, regardless how many times I cleaned the tank. Finally installed Pingel in-line filters. Clean carbs since.
Bobs850 said:
What is the best stuff I can buy to flush out the inside of the tank?

Rent a concrete mixer, get some clean sharp-edged gravel (or even better small grinding stone as use in vibratory grinders), loads of old cushions and blankets and some acid like the CLR already mentioned - if the rust is pretty light citric acid will do. The mixer will do the shaking for you - just make sure the tank cannot touch the inside of the mixer.

You could also strap it to a wild bull ride if there are any of those around still.
A standard household clothes dryer will work fine, just wrap the tank in an old quilt.
If your ready to try the dryer thing you need to build a wood frame to hold a box on the center line of the drum. You need a dryer with a big opening the Whirlpool with a bottom hinged door comes to mind same dryer has many brand names. You also need to turn the box end for end to get total burnish with about 20-30 1 1/4 long drywall screws. After the burnish is done a small box of lead shot will leave a serviceable coating in the inside that will go many years with no coating. No heat spin only cycle... Don't come to me if you get wood sprinters in your jeans later.....
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