Yes, I left the tank open for a long, long time and this is what I got:



Yep, the residue in this filter reacts to a magnet.

I have some options, I can treat the backup tank which probably has the same issues or remove this one and have it clean and coated. Having one cleaned and coated is a must at this point. Where do I get this done?

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84 300SD
85 380SE
83 528e
95 318ic

Look in Hemmings. Used to have lots of vendors doing this. Or call a local radiator shop to boil it out

I haven't seen a radiator shop in over a decade, the owner told me he no longer used the good chemicals due to EPA torture.

I suppose I though they'd all died out.

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84 300SD
85 380SE
83 528e
95 318ic

POR 15 used to have a kit to coat it. Is that rust from water in the tank?

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

The gas engine in that body hadn't run in almost a decade. I'm taking my spare tank to the radiator shop and having it done by someone who can vat and coat it correctly. I can remove the rusty one and install the other immediately if I do it that way.

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84 300SD
85 380SE
83 528e
95 318ic

The folks here do not treat/recoat the inside of the tank. Will rust find its way to the injector pump if I do not vat the tank?

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84 300SD
85 380SE
83 528e
95 318ic

Any chance the rust finds it's way to the IP and damages the unit, anyone?

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84 300SD
85 380SE
83 528e
95 318ic

This post is confusing. You say the radiator doesn't "vat" the tank. Are you saying the shop won't clean the interior of the tank?

If they clean the interior then coating the tank is not required. You can do it if you want but coating is usually used for a "seeping" type of leak.

If the interior of the tank isn't boiled/cleaned then the rust won't be removed. Any rust will indeed find its way past the fuel filters and into the injection pump. The existing filtration system will only catch particles above a certain size. Finer particles will pass and enter the pump/lines/injectors.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

I was not aware the inside of these tank were not coated. I'm not sorry that I was so ignorant but I have a bit of remorse that it was so easily revealed.

BTW, the tank is original installed in the gas body which I've installed the om617 engine/trans. Then tank sat with a small amount of gas for some years and if I'm remembering correctly, it had all dried up by the time I got a few gallons of diesel in it.

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84 300SD
85 380SE
83 528e
95 318ic

If the shop did clean the tank then you are good to go.

Coating the tank with after market products can cause problems if the coating does not adhere completely to the inner metal. Sometimes it is a necessary evil but I'd avoid it if at all possible.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Thanks, Mike D.

I made some assumptions which make me look quite brainless. I've put a diesel engine in a gas body, both Gen I w126ers. The gas tank sat empty for years and that bit of rust showed up in the first primary filter after I cranked the diesel engine.

I intend to vat the diesel tank which is sitting out back then replace the gasser tank. I will not treat the inside of either tank.

Sorry for confusing you, I wouldn't have done it if I hadn't been confused.

I made some assumptions which

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84 300SD
85 380SE
83 528e
95 318ic

The guy said they wouldn't vat it. Just a guess, I'm thinking the fuel buildup in the tank might contaminate his vat. I brought the tank home rather than paying the people 200 bucks to do what I believe can be done at home. Mind you, this is not the tank which produced the rust in the filter of the OP.

The worst of the rust in at the inlet and extends just below the guard inside the neck. I used a flashlight and did the best possible to inspect the top, rear and front of the tank (as it would sit in the car) and found no rust except for the bottom in the location of the hole for the screen to mount. I suspect the bottom and neck may be the only spots with rust and it appears the rust in the bottom of the tank is surface rust.

Here's the photo of the rust residue on the bottom of the tank at the screen outlet:



Here's one of the inside of the neck:



The rust only extends a few inches past the camera view.

I can certainly strip the rust from the neck by dipping the neck into a bucket of something to dissolve the rust but I'm not sure what acid to use. I'm thinking a solution of citric acid and water but I don't think the concentration used to flush an engine cooling system is going to do much with the rust in the filling neck.

Any advise on how strong a concentration of citric to use?

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84 300SD
85 380SE
83 528e
95 318ic

Evap-o-rust works well.

Maybe use a USB endoscope to view inside the tank ($15 ebay). If just surface rust, you could pour in phosphoric acid to slosh around and sit for a few days. Wash out with water. Add bolts and stuff to shake around and break up the loose converted rust (iron phosphate). Works well for me on rusted car parts. For lots of nuts and bolts, I shake them in a jug w/ water and keep repeating many times until I no longer get black particles. Cheapest is probably "concrete etch" at Home Depot, but in many other products like Evap-O-Rust. If you were near-by, I have a spare fuel tank (rust-free CA).

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

This is just inaccurate, I want to set the record straight for future readers of this thread. If you use the POR 15 kit and follow the instructions you will most likely have a completely clean tank interior free of rust. The coating prevents future rust. I have done several tanks this way. It is a pain in a** though.

The key to a successful POR 15 tank treatment are some hot sunny summer days to dry out the tank after each treatment step. You cannot get the treatment to work on cool days or when it is wet.