How to STOP a rusting Fuel Tank

Hi all,
My Port fuel tank has an external rust spot that I am having a problem stopping.
The rust spot is about 6" wide and about 6" tall and is located on the bottom aft outboard corner of the tank.* Of course its a bit difficult to get to.* I can barely reach it.
I used OSPHO on the rust spot about 9 months ago and painted it with Rustoleum enamel paint.*
I went to check on it the other day and the rust was worse.** Some layers of black iron steel actually pealed off.** After cleaning the area as well as I could, I hit it with more OSPHO to inhibit the rust and did NOT repaint it this time thinking that maybe the paint was somehow making it worse (holding in moisture or something).
Any ideas on how to cure this rust spot?* I want to avoid having to put in a new tank someday
Thanks for any ideas.

Steve

Strip and clean it all up and use Por 15. It's an automotive product and you'll probably have little trouble finding it. You only need to get the loose rust off. It's wonderful stuff and brushes on so well it's fun to apply. Was developed for automotive chassis use.

Steve, I've use a product called Corroseal, which is a water based product that theoretically chemically converts the rust into a stable molecule that you can the paint over.* If it were me, I would use Awlgrip 545 primer over the Corroseal, after letting the Corroseal cure for a couple of days.* If you don't see reoccurance of the rust, then I'd coat over the 545 primer with your choice of colors of top coat.* This seems to work on exterior spots I get on a steel hull, so perhaps it would work for you.

Hope that helps.

First determine where the water is coming from - then stop the "leak." Is the tank rusting because their is water in it? If so, external treatment is for naught.

Marine Tex or JB Weld would work if prepped well but not much prep is needed for POR 15.
And since you can barely reach this spot.....
Permatex may work well too.

I had the Tanks thoroughly cleaned about a year ago.* There was only about 3/8 of an inch of "sludge" in the bottom - no water to speak of.* Additionally, I use a fuel conditioner regularly.**The inside*of the tank looked great when the inspection ports*were off, so*the tank is not rusting from the inside.

My question now is, is POR 15 and/or Corroseal basically the same thing as OsPho?* OsPho is what I used on it.***OsPho is suppose to stop the rust and turn that into a paintable surface.* OsPho did not seem to work well, as the rust came back worse than before.

Any other insights would be appreciated.

Thank you,

Steve

Ospho changes the rust to black crap, but it does it weather the rust is well stuck to the tank, or not.

Rustoleum primer MUST be used on oil free surfaces , not on black crap on the surface.The primer them MUST be covered with paint for it to work.

I would wire brush or sand all the loose crap, wash 3 -4 times with acetone to get rid of ALL the oil, and paint away.Cheap paint , expensive paint , no matter, CLEAN & OIL FREE matters.

My question is why is it still rusting?* Must be getting moisture/water from some place? Find/fix the cause/source first.* We had some deck leaks but I refastened/caulk the deck and with the pilot house canvas no more damp/wet tank tops.* I used zinc primer.

If the rust extends around the back and/or the bottom of the tank and you don't get to that also , your efforts will be for naught. The rust will simply come back from the untreated area.

If a salt water leak started this, it may have saturated the wood the tank sits on. You may need to try to get something under the tank to isolate it from the salted wood. Then clean and repaint. Same for a fresh water leak although that should be easier to deal with????

Is there still a leak present. If so the rust will continue.

Can you drain and lift/shift the tank?

Taras,
If you do use Por 15 don't use any primer that's not recommended on the can. Por 15 is not regular paint. It has very low uv resistance and should be top coated w a por 15 product called "Chassis Coat". I think you can top coat Por 15 w most any finish though. When I had my gear box rebuilt I insisted they apply Por 15 instead of the spray paint they usually use. I's black but so is my Mitsu engine. Wish it was coated w Por 15. One needs to remove oil, wax ect but not all thr rust*** ...just the loose stuff. It does not work like Ospho and I don't know what it is but I sure like the way it works.

Try trimming the boat differently so the moisture is moved to another area.* I change the trim of the Eagle during the year.* It could be condensation.* Might try some Dry Ease pots to absorb the moisture.* I have 8 Dry Ease pot in the bilge area that is not heated.* Our bow thruster is*SS so it tends to have condensation, but with the Dry Ease pots its dry.* ****

So let me ask a dumb question.....our trawler has some rust spots on the tanks. Frankly, like all trawlers, I figure a tank replacement job is just a matter of time. We're in freshwater and the boat has been in freshwater for at least about 14 years. No leaks...kept under covered roof last 14 years, etc.
I am going to clean up the spots i can get and paint but what of the tops, etc. where you can't get to them? We just pressure tested them the other week and they are holding great now but we all know old trawlers= new fuel tanks at some point in time.

P.S. Anyone want to come pull my engine and cut up the old tanks in place for me on my trawler? I will provide in exchange: 3 free meals per day while work is on going, icy cold and free beer in the evenings, use of my laptop to check your email and post on trawler forum while taking breaks.

GOOGLE "air chisel" with a contractors compressor and $100 tool your tanks can be removed before the first case of beer is gone.

FF, I am not sure what you mean. Perhaps you can come to my boat and demonstrate for me? *Please bring 2 suitable replacement tanks with you as well as I fear i may have questions on the replacement portion of the project as well! *







air chisel may be easier route than a sawzall but neither option sounds like fun at all and hopefully I won't need to do that fun little project for several more years! *

*
A saw saw (spelling) works well as I cut open our 30 year old middle tank to have repaired/welded.* One of the plant welders crawled inside the tank and welded it up. I heard just this morning he passed away!* *We used two wet vac as smog hogs.* So try to repair the tank first.***When it comes to replace, I plan on leaving the old tanks in place using them as frame work and*insering multi smaller plastic tanks rather than one big tank.* ****

Phil Fill wrote:

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A saw saw (spelling) works well as I cut open our 30 year old middle tank to have repaired/welded.One of the plant welders crawled inside the tank and welded it up. I heard just this morning he passed away!* We used two wet vac as smog hogs.So try to repair the tank first.When it comes to replace, I plan on leaving the old tanks in place using them as frame work and*insering multi smaller plastic tanks rather than one big tank.

Click to expand...

Saws All???

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I recaulked my decks 3 years ago.* They did a really good job.* I then applied 3 coats of Semco (Neutral) to protect and watertite everything.* The color of the teak turned out really nice and there are no leaks from my deck, so there is never any water in my bilge or anywhere else.

Since there is no water coming in, I think where I went wrong is that I did not "primer" the bare metal as "FF" suggests.* I justed cleaned with OsPho really good and then painted with Rustoleum.**

Sounds like putting Rustoleum primer down is the key step I missed.

Thanks All for the thoughts!

Hopefully this time it will be a more long term fix.

Steve

Tony, I cut out my tanks a year and a half ago. *What a nightmare. *One was very bad and had to go, the other, in retrospect I could have left in and repainted. *i could probably have repaired both. But they are ticking time bombs. *I wanted to start fresh. *The engines were already out.

If you do want to do a major repair, once you pull the engines and take out the soundboard and beams that hold the tanks in, you can disconnect everything and move the tanks, one by one. to the middle of the bilge so you can get all the way around them to paint/repair. Works better with two guys. *I did it myself with big pry bar. *Once you lift them onto the center stringers, you are good to go. *At that point, you'd probably want to fabricate new aluminum tanks anyway.

Carey wrote:
Saws All???

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Sawzall - Milwaukee Tools' brand name for their foxtail saws.*

http://www.milwaukeetool.com/Sawzall/SawzallHome.aspx


http://www.milwaukeetool.com/Sawzall/SawzallHome.aspxRight up there with oxyacetylene torches and high explosives for taking things apart. (And maybe air chisels - haven't tried one yet.) Just cradling a 14 amp Sawzall will bring an evil grin to your face.

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Why aluminum?

I been using zinc primer which holds up well.* It its good enough for out drives it good enough for my tanks

Oh, I used Rustoleum marina primer and gloss to paint the roof this summer seems to be holding up well*in the constant rain and walking on.** Next summer I will know how*well it held up.*

-- Edited by Phil Fill on Saturday 8th of January 2011 10:26:15 AM