TheSamba.com :: View topic - Anyone used OSPHO for gas tank surface rust?

Fri Aug 21, 2020 11:43 am

I have a gas tank with JUST a bit of light surface rust at bottom, very minor. In severe cases I use Muratic Acid and then a tank sealer but this is fairly minor surface rust I just want to clean up and leave as is.

Was wondering if anyone out there has used OSPHO in a case like this and just ran it afterward (no sealant). I have gallon of Ospho here would save me a good amount of $$ on acid and sealant if it works.

Thanks

Fri Aug 21, 2020 12:37 pm

tristanblue wrote: I have a gas tank with JUST a bit of light surface rust at bottom, very minor. In severe cases I use Muratic Acid and then a tank sealer but this is fairly minor surface rust I just want to clean up and leave as is.

Was wondering if anyone out there has used OSPHO in a case like this and just ran it afterward (no sealant). I have gallon of Ospho here would save me a good amount of $$ on acid and sealant if it works.

Thanks

Yes.....I have found that is the best way. The problem with sealers is making absolutely sure the surface is prepped well enough and then...that the tank sealer is cured well enough and not "spoiled" by any contaminants.

Especially epoxy based sealers. If teh wrong kind of vapors or too much moisture get entrained....the epoxy can be week and not adhere.

When using phosphoric acid based cleaners...take a look at their mixing instructions...if any.

Products like the Jasco metal prep and prime (my favorite...and no longer available)....it needs to be diluted about 2:1 to be normal "Ospho" strength.

If you do not dilute it.....it acts as pretty much a rust "dissolver". It will act a lot like muriatic acid but will not work as long as muriatic will. It will eat the rust down to clean metal.

But when it does that....there is no more rust to convert to ferric phosphate....so you do not get that layer of black oxide protection. BUT...in a tank even half full of fuel there is not much oxygen....but with ethanol....I try to take better precautions.

The other issue is that most of these products know that when you get down t bare metal and there is no rust to convert....they have to keep it from re-rusting and most leave a thin layer of polymer sealer on those surfaces. Not what you really want in a gas tank.

So this is all in the method of application.

1. if you have crusty rust...use the product full strength or use muriatic acid. to dissolve it fully. Then neutralize with baking soda and water and rinse several times.

2. Rinse it out with water before it dries to prevent that polymer film from forming (if you used Ospho)

3. Then dry the tank totally....allowing flash rusting. No you have a very thin, even layer of rust inside.

4. Now pour diluted Ospho in to convert that to black oxide. Let dry 24 hours.

5. Pour in acetone...and use a swab with cloth and a stick to rub down a much as you can and dissolve any thin polymer film areas.

This is just fine and will protect very well and not rust if you keep the tank full. Ray

Fri Aug 21, 2020 9:52 pm

Yeah that sounds like the old method I always use for really crusty rusty tanks, Muratic acid, rinse, dry and then POR-15 tank sealer. Can't count how many tanks I have done over the years like that and ZERO problems.

But this tank is super clean...just a tad or surface on a couple spots on bottom, probably doesn't need cleaned but it is in a bus which is a pain to pull so gonna clean it up. I was think just sloshing some Ospho around, drain and let sit and use. I know Ospho will act as a metal prep on bare steel (stated in their tech sheets as well). We use it at my dad's shop for cars we take down to clean, bare steel. It will protect the bare steel from rusting while we work on it for weeks and months even. We then DA it and hit with Prep Clean when ready to shoot epoxy primer. I was hoping the Ospho would do a similar thing inside the bare steel tank. What little rust is there would be converted and the rest of the bare steel would be prepped.

My one concern was Ospho does leave a thin coating on the clean bare steel and I wanted to know if that is impervious to gas or not? Will it dissolve and cause issues-problems. I guess I could try it and find out. I was just hoping someone else had before me.

Sat Aug 22, 2020 7:59 am

I finish up all my tank cleaning jobs with it, that grey layer helps prevent surface rust, it doesn't dissolve in gas. I have found a couple hard black bits in the filter if there was a corner where it sat and built up. Rinse it out, dry it fast with a leaf blower (or shop vac in reverse) and slosh around 1/2 cup of ATF once it's dry if you don't plan on putting gas in it immediately.

Fri Oct 02, 2020 11:16 am

I sent Ospho an email about this and here is there response.

Quote: Ospho can be used inside a gasoline tank. You want to apply enough of the Ospho to the inside of the tank so that you can ‘slush’ it around. Leave the Ospho in the tank for 30 minutes, slush every 10 minutes, drain tank, Let stand for 24 hours. Then apply a small amount of gasoline to the tank. Slush it around to remove any powdering or residue left behind. After that you can mount your tank and insert gasoline. Ospho will not affect your fuel system or filters.
Regards,
Stuart Wright
www.Ospho.com

Fri Oct 02, 2020 3:48 pm

tristanblue wrote: I sent Ospho an email about this and here is there response.

Quote: Ospho can be used inside a gasoline tank. You want to apply enough of the Ospho to the inside of the tank so that you can ‘slush’ it around. Leave the Ospho in the tank for 30 minutes, slush every 10 minutes, drain tank, Let stand for 24 hours. Then apply a small amount of gasoline to the tank. Slush it around to remove any powdering or residue left behind. After that you can mount your tank and insert gasoline. Ospho will not affect your fuel system or filters.
Regards,
Stuart Wright
www.Ospho.com

Yep...same process. So gasoline will work as well as acetone by their instructions. Fine by me!
Ray

Fri Oct 02, 2020 5:12 pm

raygreenwood wrote:

Yep...same process. So gasoline will work as well as acetone by their instructions. Fine by me!
Ray

Actually does not sound anything like the methods you posted above :lol:

Fri Oct 02, 2020 6:50 pm

Although the theory sounds good he's rather optomistic about getting it all out of the tank later, VW tanks (and most others) have some sort of lip on the inside of the openings that prevent full drainage, there's always a little bit left in there.
I'd still force dry it right after treatment, a puddle of that stuff builds up hard black crystals that stick until later when you don't want them loose in there.

Fri Oct 02, 2020 9:24 pm

tristanblue wrote: raygreenwood wrote:

Yep...same process. So gasoline will work as well as acetone by their instructions. Fine by me!
Ray

Actually does not sound anything like the methods you posted above :lol:

Its exactly the same...except they do not make any notes about treating crusty DEEP rust or strength of any other product. Anything over about .003" to .005" cannot be easily treated with Ospho in its "out of the bottle" strength. It takes multiple treatments.

If you read my post carefully....for that....I made notes about the same type of product at 2.5X the strength and about Ospho.

The polymer I was speaking of....what do you think the "white dusty/crusty" residue they were speaking of that requires a gasoline rinse is? :wink:

To put it simply....it needs to be washed with a solvent to remove it (gasoline is a great solvent).

If you actually read the TDS for Ospho......and most other phosphoric acid based rust converters....THEY suggest ACETONE.

I don't just work with phosphoric acid products cleaning gas tanks. I work with these chemicals and many others for a living.

Ray

Sat Oct 03, 2020 2:06 am

First off you guys lost site of the original post.

Busdaddy you are talking about a tank thick with crud and leaving behind crystallized rust. Take a look at my original post guys...it says minor surface rust just at the bottom.

Ray, you gave 10 unnecssary steps to mutiple problems all at the same time. Talk about a cluster f### You say to use ospho, then neutralize, then rinse with water, then let the whole tank flash rust so you can ospho that AGAIN and turn it into the black oxide. You lost the original post buddy.

The original post was about a gas tanks with a light surface rust at the bottom. You put in the Ospho, slush it around and drain. Leave for 24 hours, rinse any loose powder with gas and you are done. This is exactly how you use Ospho on any surface, apply let dry and remove any loose dust. You do NOT want to do any other steps to remove any polymer (if it even is polymer) The Ospho coating left over is what protects the steel and yes it does NOT need rust left over to convert into a protective coating. It WILL coat and protect bare or clean steel (read their tech sheet). I have used Ospho extensively on bare CLEAN steel and it indeed leaves a protective coating. It actually has film build and can be sanded and creates dust. This coating is what is left behind in the gas tank as well and what protects the steel from rusting and according to Ospho Tech guy it is 100% SAFE in fuel system and is NOT affected by gas or alcohol.

Now again this is for a tank with minor surface rust. If you have heavy gunk and rust THEN yes indeed you should do the Muratic Acid clean first and then the Ospho or coating of your choice. But follow manufactures instructions!

So I did exactly as the tech from Ospho described. I poured in a couple cups, slushed it around every 10 mins for about half an hour. The surface rust in my tank completely disolved. The tank was 100% clean and gray inside. I drained the residual Ospho and then let the tank sit and dry 24 hours. It dried to a perfect gray coating inside. Not a sign of any white residue (or black crud). It had the same look-finish as all the body panels I use Ospho on when prepping a car that has been taken down to bare steel.

Ospho is wonderful stuff for light surface rust and bare steel IF and when you use it the right way and do not deviate from the steps the manufacturer lists in the tech sheet. And NOW we know it is safe to use as a mild cleaner and sealant in gas tanks as well. (Ospho really needs to that info on their Tech Sheets!)