General => Douglas Motorcycles - General Discussion => Topic started by: Sgtbiro on 25 May 2021 at 18:26

Title: petrol tank flush
Post by: Sgtbiro on 25 May 2021 at 18:26
Hi all i need to flush my Dragonfly's petrol tank and was wondering what was the best thing to flush it with, i dont know weather to use petrol or could i just use some really hot water.
and make sure it dry before putting any petrol in it.

Cheers Kevin..
Title: Re: petrol tank flush
Post by: cardan on 26 May 2021 at 00:19
Hi Kevin,

Depends on whether you are trying to remove rust, gunk, or something else!

I use really hot water with detergent, plus a handful of nuts. Shake like crazy for a long time. Repeat if necessary. Wash with clean hot water, rinse with methylated spirits to dissolve any remaining water. Allow to dry, then rinse with oily petrol (or squirt with WD40) to stop new rust.

If it's gunk, you might need to use acetone or similar, without nuts, but be aware of fire/explosion risk.

Title: Re: petrol tank flush
Post by: EW-Ron on 26 May 2021 at 08:56
but be aware of fire/explosion risk.

A not inconsiderable matter.
Also, best done outdoors, so the fumes can't get you either ...
Title: Re: petrol tank flush
Post by: Sgtbiro on 26 May 2021 at 19:26
Thanks guys I was leaning that way but itís nice to get peopleís opinion thanks again.
Cheers Kevin.
Title: Re: petrol tank flush
Post by: yosemite on 26 May 2021 at 20:48
Remember if you use acetone it will rapidly remove any paint it comes into contact with.
Title: Re: petrol tank flush
Post by: Dads bike on 27 May 2021 at 19:38
Evening Kevin
If it is just surface rust, internal of the tank, no oil or varnish contamination. Then I use warm water mixed with Molasses mixed at 4:1.
Use cheap animal feed Molasses from your local animal feed store itís about £8 a gallon.
Mix it up with warm water, fill the tank and leave for about 48hrs, drain the tank into a container for future use on other rusty parts and flush the tank with clean water, it should come out back to bare clean metal but will rust again very quickly unless treated with an oily solution.
The chemical reaction of the molasses with (iron oxide), rust, makes the rust missable with water I.e the rust dissolves into the water. The longer you leave it the cleaner and itís not toxic.
Note it only works with iron and steel, wonít work on Alloy, brass etc.
Not witch craft, honest.

Title: petrol tank flush; electrolysis
Post by: patrickwhitty on 28 May 2021 at 06:43
I haven't tried the molasses method though I believe it works well. I have a vast plastic water tank full of washing soda solution which I use for de-rusting quite large pieces of car. It is slow but very effective and it is the best paint stripper I have ever used. The paint simply slides off like a wet transfer. I have never used it for the inside of a tank but it would work well enough, there are several links on the internet to using the method including some on de-rusting the inside of fuel tanks  You need a battery charger, the negative lead is attached to the piece you are working on (the tank) and the positive lead is attached to a piece of scrap steel. The tank is filled with washing soda solution and the scrap steel suspended so that the lead is above the solution and it bit of steel doesn't touch the tank. Switch on the power and leave it. Bubbles of hydrogen will form on the inside of the tank so it is better to do it in a well ventilated area. Like the molasses method, it will only work on iron or steel. The rust is chemically converted back to steel, the scrap steel gets very rusty and eventually falls to bits. You can't 'over cook' it. When I first set up my tank I bought a fancy battery charger which could run at a very low rate but it was so clever it told me my battery was faulty and refused to work. If it was that clever it should have known it wasn't a battery. The washing soda never goes off and it is non-toxic. Eventually it evaporates, you just add more water.
Title: Re: petrol tank flush; electrolysis
Post by: EW-Ron on 28 May 2021 at 23:02
The rust is chemically converted back to steel,

That part is not quite correct. ?
The hydrogen forming on the steel surface breaks the rust particles free, and they fall off.
Or something like that. Molasses does something similar. As does citric acid etc etc.
The sludge in the bottom of the tank tells the story ...

You need a blast furnace to make clean fresh steel from rust, not necessarily in one operation either.  BIG energy.
Nit picking ?