Topic: Put gas into gas tank after phosphoric acid etch?

[Hondawggie]

Hi all, long time no time to work on my bikes. 

I have a 1976 CB550 Honda and I saw some slight surface rust on the inner tank surface.

I bought a gallon of 'de-rust etch' which is basically phosphoric acid, somewhat diluted.




I pulled the tank, drained the gas -- it was old and I then put 1/2 gallon of lacquer thinner in the tank for a few days, shaking the tank periodically, to make sure any old gas got dissolved. 

I then opened the tank fully by removing the petcock and the gas cap and drained the lacquer thinner and let the tank sit at ambient temps (here it's about 70 to 85 during the day now) for 3-4 days.

Lacquer thinner evaporates fairly quickly.

I then poured 1 gallon of my phosphoric acid-based de-rust 'etch' product into the gas tank and let it sit in the tank for 5 days, and I shook the tank each day.

BAM!  NO MORE FREAKING rust on the inside of the tank.

So I'm about to drain out the phosphoric acid from the 550 tank and need to know this:

What should I do to the tank, besides letting it air out a bit, before putting gasoline back in?

Ie.  if there's any phosphoric acid residue on the inside surface of the tank, will it have a bad reaction when I put gasoline back in the tank?

[Davez134]

I remember when I did my last tank, it flash rusted rather quickly after dumping out the acid. I read that you need to neutralize it before dumping, so I put it back in until rust was gone again. Then added some baking soda to bring the pH up. Then dumped again, rinsed with acetone, filled with gas. Stayed rust free.

[b52bombardier1]

I guess I'm too much of a POR-15 urethane tank liner zealot to comment very much here.  I would worry about more than flash rust eventually and would run an inline fuel filter if I did not put in the urethane.

Rick

[flybox1]

You gotta rinse it REALLY well.
water water water....hose it in w the tank upside down.
then 1 pint acetone - shake and empty then fill with gas.

[Don R]

Put some synthetic 2 stroke oil in the gas when you fill it, that will help too.

[ekpent]

 All good suggestions.  I'm lucky because I have an older sears shop vac that also has a blower function that I rig up and blow the "165 mph" air through the tank to dry it out very quickly and get gas into it asap with a little 2-stroke oil if its not topped off soon. Chemicals like acetone will help break down the water for better drying but it will flash rust quickly once exposed.

[flybox1]

If you have a good phosphoric coating, there is nothing to flash rust 

[Hondawggie]

If you have a good phosphoric coating, there is nothing to flash rust 

Okay that's why.   I see no flash rust in the tank 2 days after I removed the Phosphoric etch.

The thought of flushing that tank with water -- oh man.   I didn't do it.  Couldn't bring myself to do it.  So I said "I'm gonna keep an eye on it and hope to get lucky, I can always put the phosphoric acid back in again if I have to."

No water in the tank thank goodness.  And no flash rust.


I'm gonna give it a rinse with acetone as suggested above before filling it with gas -- is that the right way to go?

[flybox1]

any moisture in there at all?
If there is ANY leftover of the phosp solution, it will not dissolve in the gas, and clog everything (luckily I had an inline filter  )
If its pretty dry in there, i'd just rinse it out w/ some old gas instead.  1 pint - rinse drain, repeat, and on the second drain, look for floaties.  repeat if necessary
If its relatively clear, top it off w gas and go for a ride.

[Hondawggie]

any moisture in there at all?
If there is ANY leftover of the phosp solution, it will not dissolve in the gas, and clog everything (luckily I had an inline filter  )
If its pretty dry in there, i'd just rinse it out w/ some old gas instead.  1 pint - rinse drain, repeat, and on the second drain, look for floaties.  repeat if necessary
If its relatively clear, top it off w gas and go for a ride.

Okay -- I'm not in a hurry; I'm going to used some of my lawn mower gas for a couple cycles as you suggested then let it completely air out.