[pushrod]

Anyone use vinegar to remove rust inside a gas tank? Helping a friend get his bike back on the road after years of sitting in a shed. Overall it's not in bad condition and ran ok when he parked it. Gas tank is still solid but has a good bit of rust and scale inside. Don't want to destroy the paint as it's still in good condition. I've heard a product called Evapo-rust or something works pretty good. Any suggestions?

[Vicious]

if the rust is not a lot Coca cola is the best

[ace.cafe]

Vinegar works fine. It just isn't real fast.
If you put a bottle of vinegar into the tank with some driveway gravel, let it sit, and periodically rotate the tank around to get vinegar everywhere and let the gravel slide around inside to work as a light abrasive to knock off the rust surfaces, it will do fine.
Takes at least a few days and maybe a few weeks, depending on the severity.

[Boxerman]

if the rust is not a lot Coca cola is the best

Its the small amout of phosphoric acid in Coke that removes the rust. Why not use just phosphoric acid without all the sugar and other stuff?

Frank

[Vince]

     I have had tremendous success with a product called Kreem. The kit consists of a three pack with an acid, a neutralizer, and a protective liner. They also have a mask you can brush on to protect the paint. Use these products in a well ventilated garage.
     Remove the petcock and anything else from the tank. Make plates or use corks that will seal the tank. Check with water to ensure that you have sealed up the openings.
     Pour in the acid, then fill with hot water. Position the tank over a pan to catch any drips/leaks that may develop. Leave it for at least 2 days. Carefully drain the acid into a container for transport to a hazard disposal facility (check your local garbage dump/landfill).
     Fill the tank with water and check for the leaks that may occur when the rust is dissolved. Any leak must be repaired now. Brazing is best. Remove the plates or plugs. Get a guy that knows how to deal with welding a gas tank as this is a dangerous procedure. When the leaks are fixed, pour in the neutralizer. Shake it around, then pour it out and dry the tank. You can use compressed air or put it on an oil filled radiator for a while. When dry you may find a light coat of rust. This is OK. Leave it alone.
      Pour in the liner and turn the tank over and over to get a thin, even coat. Position the tank to get excess liner fluid over the petcock hole, then let it drain out into a pan or garbage pail.
     Now walk away for 10 days. Let it set up completely. Clean up any flash-over and any mounting threads that may have gotten covered. It is now ready for service.
     Two of my own bikes have this treatment. My XS650 has been perfect inside for almost 30 years. I've repaired many customer tanks with this product and procedure. It works and it is permanent.
     

[ophaschillm]

Apple cider vinegar and salt worked best for me. Just fill up the tank and shake it every now and then. The entire process took 2 days but may be longer depending on the rust. Then use water and baking soda to neutralize the acid and then rinse with gasoline a few times and leave it filled to make sure it doesn't flash rust. Can also add premix just to make sure.

[Tarnand]

     I have had tremendous success with a product called Kreem.     [...]     You can use compressed air or put it on an oil filled radiator for a while.  [...]

??  I am confused. 

I have done just the procedure you described.  Worked fine.  I am just completely confused about the oil filled radiator . 
The Kreem is apparently available (that is what I was told) in two colors - red and white.  Get the white one.  You can buy it on eBay for some $35.  Istructions on how to use come with the package.

[mrunderhill1975a]

I have good results using electrolysis with Washing Soda (not Baking soda), battery charger, tennis ball, steel anode.

See this link for the setup and procedure:
 https://www.motorcyclezombies.com/rebuild-tune-motorcycle/carbs-fuel-air/remove-rust-gas-tank/

[pushrod]

Thanks for all the tips, I think he's gonna try some small steel ball bearings or nuts inside the dry tank then wrap the tank in an old sleeping bag and center it in his dryer, then pack blankets around that to keep it in place and turn the drier on with no heat, sort of like a big rock tumbler to loosen  up the scale (he saw it on Youtube) and then maybe try the vinegar and see how that goes. I think this crappy gasoline were forced to use with the ethanol mix is why this happens so much. I've been adding a small amount of 2 stroke oil in my tanks for over the winter months and that seems to work to keep my tanks pretty much rust free.
 

[tooseevee]

??  I am confused. 

I have done just the procedure you described.  Worked fine.  I am just completely confused about the oil filled radiator . 

           The "oil-filled" is irrelevant. I think he said that because that's what he has. Any heat source could be used (except fire  ). In my case I would use my milk house heater that I've spent many winters with in my garage working on cars and bikes. In fact, I've got two of them and one of the original Pelonis ceramic heaters I bought in the '80s. It's still working perfectly.

[mrunderhill1975a]

 "I think this crappy gasoline were forced to use with the ethanol mix is why this happens so much."

Don't get me started on ethanol fuel.  I'm certain the ethanol causes much of the problem. I had no rust in my '99 tank until some tree hugger forced the ethanol into fuel.  There is one fuel station in town that sells non-ethanol fuel, and that is where I now fill up.