To seal or not to seal a gas tank

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Michael_P

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After tackling some fuel issues on the 1981 380SL, I pulled the fuel tank and noticed some rust inside. The tank had already been repaired about three years ago. The strainer didn't look bad. A little brown in color, but free of clogs. There was a few large pieces of slag and MIG wire from welding, but those things seemed to be a non issue. My big concern was some rust and scale particularly at the site of repair. At least half the tank had noticable rust and scale. Long story short; I cleaned up the rust using POR-15 fuel tank sealer kit. I degreased first, then used the phosphoric acid tank cleaner. Aside from a few minute spots of light rust, the tank looks 95% clean bare metal now. I will let the tank dry for a few days and was going to seal the tank with the POR-15 sealer. This product has good reviews on Amazon, but I have Googled some horror stories of people saying the sealer would come off in large chunks, causing problems.
Now I cant decide whether to: (1)Not seal the tank at all. (2)Use the POR-15. (3)Use a different sealer or (4) have a professional shop seal it.

Any thoughts? Experiences? Will the minute spots of rust less than 5mm wide cause sealer adhesion issues?

Thanks in advance
 
I would give it another acid treatment or treat it with ospho.
I bought a pint of red kote tank sealer that I never ended up using. That's what I would use if I were concerned about the POR-15 but there maybe newer options.

EDIT: You could also use electrolysis. That's what I was in the process of doing when someone threw out my fuel tank. That's how you remove rust from a fuel tank.
 
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I'd say you're in now, so I'd go ahead with the epoxy. Maybe rinse with acetone first,

On motorcycles (which rust out at the lowest-point tank seams here) i've occaisionally sloshed some ethanol in to remove any water, but US petrol may already do that.

EDIT : Good point about the electrolysis above. Forgot about that. Never done it but it seems like it should work well. ENDEDIT
 
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After seeing a few videos on POR-15, I see how think this stuff is. This tank has 5 vacuum lines for its evap. They are about 1/8" ID. I'm starting to wonder if the thick sealer could plug these lines even if I blow them out after sealing. These evap lines stick out about an inch, but snake around the tank in various places. The lines on the inside of the tank are probably a foot long or longer. More research also pointed me to a product called Red Kote. It appears to be much thinner, thus decreasing the chance of clogging the evap lines (or so I think). This tank has loads of nooks and crannies and a round nylon baffle around the strainer. I'm starting to lean toward not sealing at all or reluctantly using Red Kote.
 
Originally Posted By: Michael_P
After seeing a few videos on POR-15, I see how think this stuff is. This tank has 5 vacuum lines for its evap. They are about 1/8" ID. I'm starting to wonder if the thick sealer could plug these lines even if I blow them out after sealing. These evap lines stick out about an inch, but snake around the tank in various places. The lines on the inside of the tank are probably a foot long or longer. More research also pointed me to a product called Red Kote. It appears to be much thinner, thus decreasing the chance of clogging the evap lines (or so I think). This tank has loads of nooks and crannies and a round nylon baffle around the strainer. I'm starting to lean toward not sealing at all or reluctantly using Red Kote.


I believe you can thin it with acetone, my scooter tank had small outlets too. If you cut it 50% you should be ok.
 
Originally Posted By: maxdustington
I would give it another acid treatment or treat it with ospho.
I bought a pint of red kote tank sealer that I never ended up using. That's what I would use if I were concerned about the POR-15 but there maybe newer options.

EDIT: You could also use electrolysis. That's what I was in the process of doing when someone threw out my fuel tank. That's how you remove rust from a fuel tank.


POR is water thin in my experience. It reminds me of old fashioned lacquer paints. When it does flake off is when I’d worry as it falls off in flakes. Those might foul your pickup eventually. If you do use it remember one thing , don’t work out of the can with a brush and never try to save any you have open by dumping the unused back in the can. It’ll jell right up. It’s weird stuff to deal with and runnier than anything you likely ever used before. It’s great on frames though after you knock the loose rust off.
 
I just got back from a place that services gas tanks. My cleaned tank passed a pressure test. The person who cleaned the tank told me not to seal it at all. I still might buy the tank in Travs link. Thats a heck of a deal. The sending unit is bolt on instead of threaded, but impedance is the same. For that $245.00+ $125.95 Shipping, a spare tank would be nice even if it needed a mild cleaning. The place that tested my tank recommended 2 stroke oil or sta-bil marine formula to prevent future rust. An old timer in back also suggested an ND oil. Any thoughts which would be the best? They also did not tell me what concentrations I should use and I forgot to ask.
 
Another vote for not sealing. Not letting the car sit with a partially filled tank is the best for a steel tank. Keep it full. Less air to condense water out of. This is the kinda stuff running MMO or TCW3 or 30ND in small doses prevents Learned that from the old B+S engines with the tank screwed to the carb. Michael P why was
tank repaired previously ? My 528e tanks rusted from the outside in. When I repaired them, the insides were clean. The only trouble was the daylight shining through the side of the tank. I applied JBWeld with a 4" taping knife to one of them.:grin2
 
I've never heard of anyone sealing an automotive tank. The theory should be the same, although on a larger scale. It might be harder or take two people to distribute the sealant. I think it would be worth it on a car that sits a lot, that has had a rusty fuel tank in the past. You can leave a half tank of E10 in there until the end of time without worrying.

If your tank has been repaired before, and you are repairing it again, it might be time for a new one if you can get it. I would coat the new one, why not?
 
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