Cleaning a rusty tank

[PotatoHead202...]

I've got some surface rust in my CZ125 488 tank.

What's the best way to clean this? I was contemplating electrolysis but wasn't sure what to use as a power source? Is there anything else I can use?
____________________
Honda VFR1200F, Honda CBF500 ABS, CZ125 now CZ175

[stinkwheel]

White vinegar works fine. Fill the tank and leave to sit overnight then rinse out thoroughly with jetted water and light surface rust should come right off back to bare metal. Immediately flush with a bicarb solution to neutralise the acid so you don't get flash rust forming, more water and dry it out as quick as you can.

I've also seen pictures of some frankly remarkable looking results using evaporust and jenolite non-hazardous rust remover.

Be aware that removing the rust can "unmask" pinholes in the metal.

If you want to dry it out quick, flush with hot water, blow as much as you can out with compressed air then rinse it out with meths and get a hairdrier in there. With a CZ tank, I'd be tempted to swill it out with a bit of petrol/oil mix to coat the inside with oil.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[ThunderGuts]

I was thinking about the tank on my C90 the other day; they are known to rust, so I keep my tank absolutely brimmed with fuel (E5) whenever it's stored. Is there anything else that can be done to stop a tank rusting, or should this be enough?
____________________
TG.

[P.]

Had amazing results with phosphoric acid as advised on here. Literally within 15-20 mins, it looked almost new.

Done 2 runs of it and rinsed it out with meths. Looks brand new.

[Robby]

Phosphoric is what I always use. Costs about 20 quid for a 4 litre bottle of 40% strength on ebay, and you can top it up with water to fill the tank to just below the filler neck. Warm water helps, but the stuff still does the job well diluted down to below 10% strength.

The rinsing out, meths and light oil (or filling with petrol) very quickly afterwards is critical. Steel loves to flash rust all over again, but a very thin coating of just about anything oil based stops this from happening.

I did step by step instructions on a thread from Paddy asking the same question a few weeks ago, search is your friend.

Whilst I do like Stinkwheel's method, a couple of gallons of vinegar is surprisingly expensive.

[P.]

[doggone]

So is it Ok just left bare metal after you stripped it back.

[P.]

I filled it with the 5l of fuel and filled up with E5 absolutely brimmed it.

Looks perfectly fine now, but I expect if I don't keep it tip top, its gonna be ass.

[stinkwheel]

[Robby]

I stand corrected. Does it still eat aluminium alloy like phosphoric does?

Whilst I'm going to stubborn and stick by phosphoric, it would be nice to have something that doesn't require removing everything non-steel from the tank on newer machines with fuel level sensors and in-tank pumps. If I could just fill the tank as is sits with vinegar and drain it out through the tap, that would be easier.

[blurredman]

To OP:

Depends what it looks like... Pictures?


This is mine in one of my bikes. It was a lot worse when I first got it. I got it in '16 and basically other than a few times when I had to declog the petrol tap in the initial weeks of using the bike (namely the reserve position channel), I've not really bothered to do anything about it other than initially shaking nuts and bolts in it and washing it out before I fixed it onto the bike.

Part of me not doing anything is me being afraid that I might introduce pinholes....


But alas, 20,000 miles of petrol, 332 gallons (or 1,510 litres), have gone through this tank since then, and to a certain extent cleaned it up a bit and made it look better.

I am however wondering when it will eventually leak through.


https://scontent-lhr8-1.xx.fbcdn.net/v/t1.15752-9/305616518_3535737173370577_7673653070247654044_n.jpg?_nc_cat=107&ccb=1-7&_nc_sid=ae9488&_nc_ohc=Cci4bi3b12UAX8BxeqV&_nc_ht=scontent-lhr8-1.xx&oh=03_AVI-8-AX-EFKsr4_1hMbNexc3l4wEqUljmZ2Jz-CS71E9Q&oe=636D8857
____________________
CBT: 12/06/10, Theory: 22/09/10, Module 1: 09/11/10, Module 2: 19/01/11
Past: 1991 Honda CG125BR-J, 1992 (1980) Honda XL125S, 1996 Kawasaki GPZ500S.
Current: 1973 MZ ES250/2 - 17k. , 1979 Suzuki TS185ER - 9k, 1981 Honda CX500B - 91k, 1987 MZ ETZ250 (295cc) - 38k, 1989 MZ ETZ251 - 49k

[Bhud]

The bottom line is, use whatever works for you. I need to do it on my current project. I use Tank Cure Rust Remover and I'm sticking to it, even though it's gone up over 100% in price since October 2020. This is because it will be rust free within a day.

Regarding the comments about phosphoric acid: that's interesting. I would have thought hydrochloric acid.

I'm not scared of pinholes appearing, because it's best they show themselves, and they're easy to fix with silver soldering (which is easier than bronze brazing).