Gas tank rust

Dave H (MI) · Jul 6, 2021

The MF 36 swather cut out in the middle of doing a hayfield a couple weeks back. What happened was this. It had not been used in years but I keep it running. The tank got rusty and when I filled it and took it to the field a lot of surface rust sloshed into the fuel and the filter started to block and it eventually quit. It will probably get yearly use now. Is that sort of surface rust likely to resolve thru use or do I need to do something else? I could hang a clean tank on the outside without modifying a nice old machine, but would rather just use the existing tank.

Fritz Maurer · Jul 6, 2021

A very large fuel filter, like what youd see on a fuel injected car. 86 Ford tempo for instance. Put it in the suction line in a easily accessible area. Change it when it starts acting funny , shouldnt take more than 3 of them. Just an example, naturally the bigger filter, the better.

Steve@Advance · Jul 6, 2021

How hard is the tank to get off?

You could take it off, dump it out, put some E85 gas in it as a solvent, piece of clean chain inside and slosh it around, try to get it as clean as possible. Dump it and blow it with the air hose, but don't use the shop vac! There may be a screen standing inside on the fitting at the sediment bowl. You'll want to take that out first. The screen is probably rotted away, be a good time to replace it.

If the tank is severely rusted it will eventually need to be replaced. I have heard good and bad about the tank liners, never personally tried it.

If it's a gravity system, best to keep the factory screens in place. Inline filters don't work well as they are too restrictive. If there is a pump, it will need to be cleaned out best you can. Put the filter after the pump. There may also be a screen in the elbow at the carb.

Fritz Maurer · Jul 6, 2021

Yea I never considered the fact that it might not have a fuel pump. I was picturing my own situation as I was typing. Sounds like your idea is better. I never liked the idea of coating the tank and trapping all that stuff in there.

Geo-TH,In · Jul 6, 2021

My boy soaks rusty axe and sledge hammers in a mold solution of food citric acid.

Then he uses flap sander to take care if the rest.
I bought a concentrated gallon of food grade phosphoric acid, smell like vomit.

Phosphoric acid chemical used in some rust removers.

Some people have used white rock inside tanks to knock rust lose. I've heard of people lifting one wheel on tractor, attaching tank to wheel, spinning tank and knocking off rust.

After getting the bigger pieces of rust off, I would soak the tank in phosphoric acid overnight and see what happens.
Then there's a special sealer you can paint the inside of the tank.
By the time you buy chemicals and tank sealers you may ask yourself if you should have bought a new tank?

jimg.allentown · Jul 6, 2021

So far, the solutions I see offered are incomplete.

First thing - phosphoric acid is the active ingredient in the 'paint over rust' products offered. They turn the rust into a hard chemical (I forget the name of it) that stops further rust and gives a stable surface to paint. That would be a good starting point.

Second thing - sealing the tank. I would recommend getting a good tank sealer offered by one of the many antique restoration companies. Look for good reviews and choose the one that best suits your needs.

Lastly - to the fellow that is concerned about how much you will spend compared to replacing the tank - Dave did say that he wanted to keep it original as much as possible. That would be the reason for spending the time and money to solve the problem.

Fuel filters are a good idea, but they are not usually well suited to gravity feed systems. Maybe adding a light duty low pressure electric fuel pump would help.

RedGreenGuy · Jul 6, 2021

I had radiator shop clean and seal mine. After cleaning it was double sealed. Tank was for Ford 3400 a 13 gal tank cost $250ish.

JK-NY · Jul 6, 2021

Is it a gravity fed fuel system ?Inline fuel filter is a temporary solution, trying to clean the tank as mentioned and installing a stand pipe with screen on the tank outlet is a solution that would allow keeping the original tank. That would allow the sediment and rust to settle to the bottom while you draw fuel from an inch or 2 above the bottom of the tank. Using a clean auxilary tank is another good solution.

Glen SW Wi · Jul 7, 2021

Ace Hardware sell the phosphoric acid. It is called Ospho. Used it by the gallon when I worker off shore on the oil platforms. It is a very mild acid and won't burn you hands.

Roger in Wisconsin · Jul 7, 2021

If the rust isn't too bad you can use a magnet with extension and a flash light. Fish the chunks out.

Geo-TH,In · Jul 7, 2021

I haven't had luck with paper inline filters for gravity feed.
They do make screen filters for lawnmowers.

Geo-TH,In · Jul 7, 2021

Rust is iron oxide.
Phosphoric acid, or any acid, is used to remove the oxygen to convert rust back to iron. Then seal tank with a special paint designed to coat inside of tank.
I can't remember what it called. I think red was in the name.
Some people use white rock with edges to help knock off larger pieces of rust.
Once I put a few small rocks with jagged edges inside a small mower tank and used compressed air to bounce the rock around inside tank.

DoubleO7 · Jul 9, 2021

(quoted from post at 09:25:42 07/07/21) Rust is iron oxide.
Phosphoric acid, or any acid, is used to remove the oxygen to convert rust back to iron.

You have made this statement before.

It is FALSE!

With a Masters degree in physics you should know that no acid or chemical will magically convert iron oxide back into iron.

Gas tank rust

Dave H (MI)

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Fritz Maurer

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Steve@Advance

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Fritz Maurer

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Geo-TH,In

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jimg.allentown

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RedGreenGuy

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JK-NY

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Glen SW Wi

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Roger in Wisconsin

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Geo-TH,In

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Geo-TH,In

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DoubleO7

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