Green Powder in the fuel tank

[Seaduck]

In the fuel tank there is a green powdery substance exactly like the green corrosion found on copper.

I have tried rinsing with neat petrol and I've removed the tank, taken the tap off (stuck a trimmed wine cork in the hole) filled it with a handful of nuts (10mm not hazel) added more clean petrol and shaken for ten minutes... twice.

But still when I run the motor I end up collecting this green sludge at the lowest point of the fuel system, the bottom bend of clear pipe between the tank and carb... its heavy enough not to get sucked into the carb but fine enough to get through the gauze filter on the tap.

Whats causing it and how do I stop it? or Could/should I seal the inside of the tank with something like 'slosh tank sealent'?

Neal

[chris]

I have had the same with my silver century, I am curious about it as well, it never seemed to affect the running of it

[Keith.P]

Sounds like you have no fuel filter in the tank anymore, which would help with the crud getting around the system.
I suspect you would need some type of caustic or acid to remove the oxide from the tank.

[RickUK]

It's verdigris (oxidation of the brass tank), brass being a copper and zinc alloy. I forms over a long time and is usually very fine. Tanks are tricky to flush out, but just multiple washings with parafin or similar should kill it and flush it out, and once you have petroil sloshing about it won't re-form. You do need to have the fuel system fairly spotless to stop potential blockages. One time I was impatient to try a motor on the back of a boat and ran it with the said green oxide in the tank - and sure enough. . . .

You certainly don't need to go to such lengths as tank sealant though --

[Gannet]

On advice previously on this site, I used caustic soda. It is readily avaiable and works really well. It also damages paint if the solution is sufficiently strong, so not to be splashed onto the outside of the tank.
It also cleans up - just for cosmetic reasons - the bronze transom bracket.

[Seaduck]

Cool, I've got some caustic soda somewhere
The paint on the tank is cream crackered anyway and the decals are loooong gone... another job for the list

As we've mentioned the outside... any ideas on whether I should try getting the dents out of the tank? or do I just leave them as 'patina'

Neal

[Stelios_Rjk]

Did you try with caustic soda? Was that cure effective? How much did you use?

Thanks

[alpinechili]

I used 1 kilo of caustic soda to 10 litres of water and immersed the entire tank in it as I wanted to remove the paint also. The verdigris had gone after a days worth of soaking, the paint just needed a bit of a scrub to remove it. Be careful if you don't want to spoil the outside of the tank. It looks nice once polished, might just coat it with some lacquer.