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'83 380SEC AMG'ed euro, '92 500SL, '91 190e 2.6 5-speed
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Discussion Starter #1
Hi everyone,

I've removed a gas tank from a '87 420SEL that was in desperate need of a flush. The tank cleaned up pretty nicely but there is rust inside (No flakes but will get worse if not addressed). To prevent problems in the future (The previous owner cut the strainer out...) I'd like to seal the tank. Given that w126 tanks are steel this shouldn't be a problem however the tank does have a plastic housing inside (Around the main fuel hose). I'm concerned that there will be an adhesion problem with any sealer if applied.

Have any of you had there tank sealed? If so, do you know if the tank was split to remove the plastic housing first?

I know best option would be to find a used tank without this problem but they aren't always available and if they are they have also been sitting with a galloon or two of old gas inside. As our cars get older restoring these tanks will become more common.
 

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1988 560 sec
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There are many products for removing the remaining rust in gas tanks , evaporust is one there are others .

Sealers are asking for trouble , first you have to remove all the rust anyway and then apply the sealer and pray it adheres . I have sealed a few bike tanks and wished I didn’t after.

A rust free tank used regularly will last forever.
 

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'83 380SEC AMG'ed euro, '92 500SL, '91 190e 2.6 5-speed
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Discussion Starter #3 (Edited)
There are many products for removing the remaining rust in gas tanks , evaporust is one there are others .

Sealers are asking for trouble , first you have to remove all the rust anyway and then apply the sealer and pray it adheres . I have sealed a few bike tanks and wished I didn’t after.

A rust free tank used regularly will last forever.
Thanks for the reply -

that sounds great but won't won't the tank rust really quickly if the metal isn't sealed? A well maintained tank wouldn't rust but I feel like treated metal will have to be treated after its etched (Which I'm sure something like evaporust does).
 

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1988 560 sec
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Tanks rust from lack of fuel and storage without fuel. Most people use a sealant to fix a tank that leaks.

If you remove the rust and use the car you will be fine if the corrosion of the tank was minimal to start and has been removed .

Seal it if you wish , just make sure if you do that the tank is Perfectly clean , rust free and absolutely degreased and dry or the sealant will not adhere.
 

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1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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On recommendation of a restoration shop, I had a [non MB] fuel tank boiled out, repaired, rust removed and then the insides sealant 'sloshed'.

Ten years later, the sealant had come loose in places, causing an intermittent fuel supply failure and clogging the carburetor passages...

It was, overall, a very expensive proposition.

I might consider tank replacement with a used unit.. I see a couple on Google .. $330 includes shipping for one from a '91 420SEL

https://mbiparts.com/product/1991-m...MI0f7c_oOE1wIVxEGGCh2EFAonEAkYASABEgLfkfD_BwE

A thought anyway.

Good luck man.

MBL
 

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350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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Two replies lost in the ozone of expired tokens. :mad:

Present day fuels are incompatible with sealants of the past. There are present day sealers that work today. No guarantee for the future...

Caswell Coatings sells a kit that is well respected int he motorcycle universe. POR-15 is even used in aviation.
 

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1986 560 SEL
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I've sealed two fuel tanks with POR-15 kits.

I do go a couple of extra steps, in that once the chemicals have been run though the tank as per the instructions, a quantity of large nuts (the kind you thread onto a large bolt) are put into the tank and shaken around to loosen up anything that's left. Nuts are retrieved with a magnet and the rust is tapped down to a corner that's reachable by a shop-vac nozzle. It's then removed.

Finally, the coating is applied.

Following the instructions to the letter is important as the tank has to be dry, arid, desert-like before sealer application. POR-15 says it will not stick to anything damp and it won't.

The first tank done remained with my son for 10 years before being sold. The rust in that tank was so bad it clogged two sets of injectors in a week.

The last one I did was only about a year ago, but that one seems to be fine as well.
 

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'91 560SEC, '91 300SE (sold), '98 Yota, '02 S-10 Hauler
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Following the instructions to the letter is important as the tank has to be dry, arid, desert-like before sealer application. POR-15 says it will not stick to anything damp and it won't
Ed, do you remember if the kit said if it could be used on aluminum ? I ask because my other project, Riff Raft, I have a brand new never installed, yet, aluminum gas tank and I thought perhaps sealing it before it's install would ward off the well known pinholes over time from water, condensate getting in aluminum marine gas tanks
 

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1986 560 SEL
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Ed, do you remember if the kit said if it could be used on aluminum ?
Good morning, Brother Wook.

I don't recall as to whether it can be used on aluminium, but I don't see why not. On the other hand, it's aluminum, so it won't rust...oxidize - yes, but it won't rust.

POR-15 products will fill small pin holes, but preventing them is another critter altogether.

I did have occasion to call them when I did the first tank. Their number is 800-726-0459. It was many moons ago, but they were very nice.
 

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Good morning, Brother Wook.

I don't recall as to whether it can be used on aluminium, but I don't see why not. On the other hand, it's aluminum, so it won't rust...oxidize - yes, but it won't rust.

POR-15 products will fill small pin holes, but preventing them is another critter altogether.
Good Morning to you also Brother Ed. I'll give em a call, thanks for the number. Like I said this is a brand new tank built for this boat but I've never installed it because of the notoriety of pinholes developing over time in the marine environment and Coast Guard regs say no drains, everything fits out the top of the tanks, fills, senders, fuel supply, vents so any water has no where to go
 

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Hi everyone,

I've removed a gas tank from a '87 420SEL that was in desperate need of a flush. The tank cleaned up pretty nicely but there is rust inside (No flakes but will get worse if not addressed). To prevent problems in the future (The previous owner cut the strainer out...) I'd like to seal the tank. Given that w126 tanks are steel this shouldn't be a problem however the tank does have a plastic housing inside (Around the main fuel hose). I'm concerned that there will be an adhesion problem with any sealer if applied.

Have any of you had there tank sealed? If so, do you know if the tank was split to remove the plastic housing first?

I know best option would be to find a used tank without this problem but they aren't always available and if they are they have also been sitting with a galloon or two of old gas inside. As our cars get older restoring these tanks will become more common.
Hello,

I have a rolling restoration with a 1989 300 SEL, and I have the exact same issue with the gas tank. Can you tell me how you solved the rusty tank? It has been a number of years, so how is the Mercedes tank doing...any problems?
 

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Smoke Silver '87 560SEC, Black Pearl '87 560SEL
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Where are you located? US? Europe?
There is a guy here in Las Vegas parting out a 420SEL and might just have a non-rusted gas tank. Quality Star Benz, 702-396-4216, ask for Jeff.

Normally I'd just go to my local Las Vegas pick-a-part salvage yard and get one but there are no W126's in the yard closest to me. But...there are several more salvage yards nearby that could have a good tank. Vegas will cook the rubber bits every time, but it is a dry heat so the metal parts don't rust.
 
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1986 560 SEL
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You might heed Mike’s advise above and try to find a non-rusted tank from a yard. Barring that, I’ve had good result from the POR-15 kits as mentioned also in an above post.
One of the tanks I sealed I’ve lost sight of, but the other is in fine shape, as I cranked and drove that car in the last week.
As far as a “rolling restoration” goes, you will need at least a week WITH THE TANK OUT OF THE CAR to do a proper job. You’ll also need an assistant for some of the work as a fuel tank is bulky to handle.
Just follow the instructions to the letter. A sacrificial hair dryer is an asset to the drying process.
 

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350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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All of the tank resealing processes rely on proper and thorough prep work.
 

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1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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All of the tank resealing processes rely on proper and thorough prep work.
Yep, you are so right John.

I don't know how many thousand dollars it cost me when the restoration shop subbed mine out for an expensive re-furb..
Five years later it was again an expensive diagnostic journey before the car could be sold.

In my prior forty years of driving enjoyment, the fuel tank had not been an issue at all.

MBL
 

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1999 C280 (sport), also 2001 SLK230
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So the other posters before me have already mentioned POR-15. I've been impressed with their rust prevention paint, but have never used the gas tank sealant. However, I'd suggest you call them with your specific question. I'm sure they will know whether their product will stick to the Mercedes plastic or not.

Any chance you can remove the plastic part and only coat the metal part?

That said, the idea of finding a used tank in a dry place like Southern Ca, NV, or AZ seems to make sense.

Cheers,

Kim G
Boston, MA
Where it's damp, and I'm now wondering about rust in the tank of my seldom-used '89 Toyota pickup.
 

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'83 380SEC AMG'ed euro, '92 500SL, '91 190e 2.6 5-speed
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Discussion Starter #17
Hi, oof old thread :) I think many of those responding are not acknowledging the plastic baffle inside of the tank. I am certain if it were to be coated with anything it would eventually fail. I thoroughly pressure washed and degreased the tank it to make sure everything was gone. After cleaning, the rust was minimal so I opted against coating it because of the baffle. I replaced the screen, hoses, and pumps, and it didn't give me any issues (~1.5 years of driving) – I sold the car after that.
 
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