What to do? - Sealing a gas tank

[Joe Cocuzza]

So here's the situation...I know it is probably a matter of opinion...

I bought a new gas tank for my 49 caddy. 

According to the seller it is made from the same type of metal as the original.

I called the seller and asked if it is recommended to paint/undercoat the tank before installing it.

The answer was "no". It was also stated that the new tank will "rust just like the original one because it is made from the same metal"?????

Sooooooo... 

Should I or shouldn't I at least try to protect the tank BEFORE installing it?

I am leaning towards cleaning the outside and spraying it with SOMETHING to prevent it from "rusting like the original".

BTW. The original tank has/had undercoating on it and did not rust on the outside at all. It was the untreated inside that rusted.

[MikeC5]

I can’t see how there could be a down side to applying an inert coating (paint, undercoat, etc.) to slow down external corrosion.  I would even consider adding a coating to the inside of the tank to prevent corrosion, such as Hirsh tank sealer, etc.  With a new tank, the inside can be prepped to ideal conditions for a good bond with the sealer.  

[Dave39MD]

The only thing you might consider is adding a separate ground wire for the sender if there is not one already.

 

Dave

[Bloo]

23 minutes ago, Dave39MD said:

The only thing you might consider is adding a separate ground wire for the sender if there is not one already.

 

Always do that.

 

 

 

 

[Carolina Chevrolet]

I usually spray new tanks with a good quality clear coat before installing.

[padgett]

+1 on clear coat.

[Larry Schramm]

Not sure how far back, but my knowledge of GM gas tanks had "terne coating" to prevent rust.  At least I believe from the '50's to the 80's when the change to plastic tanks took place.

 

Terne coating definition:

 

https://en.wikipedia.org/wiki/Terne

[AHa]

I went through a disaster of a gas tank sealing operation two years ago now. Search for Red Cote Arhhg to see my posting on that experience.  Most sealers are not designed for a new tank. Call the manufacturers to discuss this before attempting to seal the inside of a new tank.

 

Most sealers will simply peal off the inside of a new tank. The inside of the tank can be acid washed to give the sealer something to adhere to but again, talk to the sealer manufacturer first. Some tanks have a galvanized coating and galvanizing leaches oil, so sealers will not stick.

[ojh]

The 'Terne Plate' is on the inside of the tank, not the outside.  I'd use 3m Undercoating on the outside, several coats.  The aircraft industry has the best gas tank sealants, but note they are a sealant and not necessarily a coating.  You could use the PRC Desota 1422 type 'A' 1/2, the type 'A' means its liquid so you can slosh it around and the 1/2 is the 1/2hr cure time.  Type 'B' is more a putty that won't run or sag (like you'd use around the screws etc on top of the tank.

Personally I'd get some Ospho and pour it inside undiluted and let it slosh around, then drain and let air dry.  reactivate the Ospho by pouring in some more and slosh it around, drain and then rinse thoroughly with water to stop the chemical reaction of the acid on the metal.  I'm surprised the gas tank maker didn't already do the Ospho thing, that is the very least they should have done prior to shipping.

Edited December 17, 2020 by ojh (see edit history)

[Matt Harwood]

It took decades to rust and fail the last time, it'll take decades to rust again. Gamble with coatings that may or may not work on fresh, shiny metal or just leave it as-is per the manufacturer. If both GM and the guy who made the tank left them bare, perhaps there's some logic to it. I always understand the desire to make things as permanent as possible when working on our old cars, but it's also important to remember how gently and carefully they are used today--none of them will be used as daily drivers in harsh environments. As a result, the rust and other issues that we suffered through in the past are probably not going to be issues in hobby cars, at least, not those that are properly cared for. Neglect and long periods of sitting are what cause rust in gas tanks, but if you're restoring your car to use, then I bet the new tank will outlast us all.

 

Just a thought...

 

 

Edited December 17, 2020 by Matt Harwood (see edit history)

[AHa]

I echo Matt's thoughts. Anything you use to clean the inside of the tank will leave residue that may then react with any sealer you choose. When I struggled to seal my original tank two years ago I used several products that all failed due to a lack of proper instruction. I finally called POR 15 and talked to one of their engineers. They have an 800 number. He walked me through the correct process for using his product and I had great success. I called several times through the process as I was desperate to get it right and each time I found them cordial and helpful.

[ojh]

The original tank was not bare metal, I believe they used Ospho since 60's anyway, maybe earlier, before then a lot were terne plate.  But they all had some kind of protection, bare metal would have rusted quickly and messed the carbs up in short order.

[MikeC5]

I have struggled with the decision to seal the tank in my Dodge.  It doesn't leak but I was surprised at how much rust was in the in-line fuel filter after 2 - 3 years and not many miles (I posted photos of it a while back).  I decided to try and seal it after seeing that.  I have cleaned it with lacquer thinner and 2 pounds of roofing nails sloshed around, then poured out and let the tank dry.  The stuff came out very rust colored.  I have a decent bore scope and have examined the inside pretty closely and it appears that whatever loose rust there was is gone.  I then put a gallon of Rustoleum rust remover (mostly phosphoric acid) in there with the nails and agitated the tank for a good hour.  This solution came out quite dirty too and the tank is quite clean looking now.  I plan to do another Rusto treatment, then rinse with hot water, add a little alcohol and shake it up to absorb any remaining water and then heat dry.  At that point I'll start following the detailed instructions that come with the Bill Hirsch kit.  I liked that this kit does have detailed instructions and  includes a degreaser solution and etch solution prior to the sealer.  The tank does have one baffle so it remains to be seen if I can get that fully covered with sealant.

[Joe Cocuzza]

Thanks for all the replies/advice.

Maybe I wasn't very clear in my OP about what I was asking.

I DO NOT want to seal/treat the inside of the new tank as that is not recommended by the manufacturers of the sealing kits.

Also, I forgot to mention that the exterior of the tank has some sort of "oily" substance on it so maybe it already has been treated to prevent it from starting to rust. If I want to paint it I would need to remove that oily stuff before trying to paint it

I wanted to know if I should prep/coat/paint the OUTSIDE of the tank prior to installing it. I believe it couldn't hurt to do this but I want to know if it is worth the extra time/effort to do so.

Matt is correct in that the car will be stored inside and NEVER driven in the elements (rain/snow, etc) but it will not be stored in a temp. controlled garage. However, I have a dehumidifier running to eliminate any moisture that may be present." (The original tank has/had undercoating on it and did not rust on the outside at all. It was the untreated inside that rusted)"

Thanks again for all the replies. 

I suppose, after reading the replies, it is up to me to do as I see fit.

 

[Matt Harwood]

Does Eastwood still offer that "Spray-Galv" paint? That is supposed to look like a galvanized coating and it is apparently designed for just this application on the outside of gas tanks. Sorry I misunderstood the question--painting the outside, do whatever you like as long as the prep is thorough. It should probably remain silver, so even a silver paint or a clear would look correct under there at a glance and help prevent future rust issues.

[60FlatTop]

I did a lot of work underneath my '60 Electra and decided to undercoat the tank. It makes a nice contrast to the painted parts.

 

I also know the sound deadening qualities of the undercoat. I painted the tank and removed old undercoat from my '64 Riviera and it is noisier. On a future car I would go with the undercoated tank again.

 

 

[Guest]

 I washed my new tank with lacquer thinner and sprayed it with several coats of clear polyurethane.

 After a year, it came off in sheets.

 As for sealing the inside, for all the trouble involved, a $200 new tank is cheap.

[46 woodie]

Ever since the fiasco of the gas tank sealer from the '70's, I'm apprehensive to use it. Back in the '70's everyone, including me,  was using the "latest and greatest" gas tank sealer. Along came Ethanol gas and we all had trouble, as the new gas ate the gas tank sealer. Sure, the new stuff from Bill Hirsch might be the thing to use now, but what about 20 years from now when the government play's with the gasoline again? I would paint or coat the exterior of your new gas tank and leave the inside alone.

[AHa]

Well, at least I wasn't the only one who misunderstood the original post. When talking about sealing a gas tank, the mind naturally goes to the inside of the tank. In this case, the OP was wondering how to seal the outside of the tank. Haven't you heard we will all be driving electric cars by the end of the next 8 years. We are at the end of the use of fossil fuels. We need to start thinking about how to retrofit our antiques with electric motors without affecting the ambience of the driving experience. Maybe someone can invent a tablet that will make artificial blue smoke come out of the tailpipe.

[padgett]

Problem is crusty deposits when dried. Is nice when you can buy a new tank but not always available.Have heard of trying  in order of success Berryman B12,Techron concentrate,xylene,MEK. Also tried with seemingly poor effects,Denatured Alcohol,lacquer thinner,seafoam.

 

Opinion ?