When I got the car, I cleaned out the fuel tank (so I thought) but the fuel filter kept clogging so I had another try.
On YouTube, many people use vinegar - so that's what I tried and it has worked a treat.
Flushed the tank with the garden hose again and then filled the tank with 20l of vinegar (rest was water) from the supermaket - left for 24hrs.
Then I let the vinegar/water out via the drainplug (huge amount of muck came out).
I flushed again with hose, put tank plug back in, filled tank with water, undid tank plug and let the water out (more muck) flushed again with hose. More muck.
Did that cycle numerous times until the gunk stopped coming out to an acceptable level.
To dry, I then left the filler cap off, Sender unit out and cover off,plug out.
Then blew the fuel line out with a blower used for pumping up air mattresses!
Then, put some fuel in, disconnected filter inlet pipe, ran the pump and flushed line through with fuel into a tray.
Some residual particles came out but that was expected.
Then took car to garage to fill-up to the brim and went for a run.
After flushing, I waited the bare minimum of time for tank to dry because mild steel starts rusting immediately.
I hope that is helpful for the next poor person that has to clean their tank!!

 

I too used vinegar to clean out a BMW tank and essentially used the same process. It worked very well but I could see flash surface rust appearing no mater how much I dried the insides. The car is still undergoing a restoration and I did not want to use a coating with the fear of it flaking in the future. So we decided to swirl around, then drain, some diesel fuel which leaves a bit of a coating, that of course will get dissolved as the tank is filled with gas. It did seem to reduce the flash surface rusting we were experiencing. After installation in the car, as a precaution we did add during the break in period, a second inline fuel filter at the exit of the tank. We did not see any significant debris or discoloration of the see through filter.

The car is a 1970 BMW 2800CS with dual zenith carbs and a mechanical fuel pump.

Thanks
jjsandsms.

 

It may be worth trying phosphoric acid at the end of the process to convert any remaining rust and give the surface a little corrosion protection. It might also help POR/Slosh sealant to attach.

 

+1^ Peter ~ phosphoric acid is the answer.

 

As I stated in a previous post I used white vinegar to clean the tank then I used the POR15 sealant. Nearly eight years on and not had any problems or any of the sealant coming off the inside of the tank.
You can also use the white vinegar to clean the inside of your radiator. Use the same method. Fill it with vinegar and let it soak for as long as you can, maybe a couple of days or even a week then flush all that gunk out. Just like the fuel tank you will be surprised by the amount of rust coloured liquid that comes out of the radiator. Don't forget to do the heater matrix radiator as well.

 

The trick with Phosphoric Acid is that it reacts with the surface to form metal phosphate, which is a protective coating. A good start to apply your POR15 sealant to and extend it's life. As I said earlier all coatings come off sooner or later.

 

‘Pickle and phosphate’ has been fairly standard for steel products such as steel tube and later car bodies probably since the early days of the steel tube and gun barrel industries. The pickle was sulphuric or hydrochloric acid that removed rust, mill scale and almost anything else. The acid is washed off and, if the steel was going to be painted or left bare, it would go into a bath of phosphoric acid. It gives a phosphate coating that, in a mild environment, provides reasonable short term protection against corrosion and also a good key for paint. Before its use was restricted, the paint would have been red lead (is that the bottom, red layer in the original paint on our old cars?). There have always been variations in the process such as the choice of acid for pickling and the addition of a little zinc (the universal additive) to the phosphoric acid.

Nowadays, in the car industry zinc electroplating to produce Zintec sheet will be an additional stage. Even then, phosphoric acid often turns up to etch the zinc and help the paint to stick.

 

Very well put Peter. I should have explained further. I take too much for-granted with my replies.

 

Glyn, Your replies were fine. Since my first paid work in engineering was six months as an apprentice in a steel tube works, it's something I got to know a long time ago and it somehow made an impression. Possibly it seemed like useful chemistry, a subject I'd given up on as not that interesting, not to mention involving too much stuff to remember.

 

If the goal is simply to remove rust, rather than vinegar I'd suggest a product called Evaporust. It's an iron chleating agent, which chemically converts the rust back to iron. It works very well and is non toxic and also won't leave the metal prone to flash rust. Although for longer term use, you should protect the bare surface after treatment.

I found a pair of locking pliers in a truck at the junkyard one time, rusted solid. After 3 days in a bath of evaporust, they moved and worked again.

 

I use Evaporust all the time, great stuff, but at US $25-$30/gal and if have say a 15 gallon tank, vinegar at a couple of bucks a gallon looks pretty good.
Of course if the tank is out of the car, one could use less by continually repositioning the tank until all surfaces get treated. Evaporust would indeed be a better way to go, but again.......the price.

Also Evaporust can be reused several times until it looses its effectiveness.

Thanks
jjsandsms

 

You can get creative. I saw a guy who derusted a Cadillac body by putting it on stands and the built a plastic tent around the entire car, with a low point in the plastic at the bottom. He put a garden pond pump at the bottom and attached it to a sprinkler on top of the roof, which continually sprayed the body with evaporust and as it ran down to the pump was recirculated. That way it didn't take much chemical to derust the entire body.

 

Thx - I filled mine up as soon as I could so hopefully minimal flash rust. 2800CS is a beautiful car - lucky you!!

 

That is a marvellous story - very inventive. We all kinda have to be inventive, but thats a beauty!!

 

Evaporust contains Phosphoric acid and Oxalic acid in a low dose as a ph buffer. When you analyse a sample in an AA Spectrophotometer or do an IR scan their secret formula is exposed. It is readily available in SA.