W123 300D Fuel Tank - Internal Seal/Coat or not?

[dennislarock]

I'm getting Rust @ the primary fuel filter. So, I pulled a tank from the plethora of cars that I have. I dangled a small (about 8') chain in the tank and supported it. Then, I put a couple of quarts of diesel fuel in it sloshed it around and drained... a little dirty but no rust. I then put a couple of quarts of Acetate in it sloshed it around and drained... almost 0 dirt and no rust. From what I can see (I don't have a scope) the tank looks quite clean.


So, should I Seal/Coat the inside of the tank? Or, should I just install as is? The product I see the most is Red-Kote.



What would you do? Opinions Please


Thanks


dennis

[DanHoug]

Red Cote is a good product but if the tank is visually free of rust and not shedding and not leaking, i'd leave it as is. with coatings, there is ALWAYS the danger of them peeling off. there's 2 screens and a filter in the system so even if some flakes come off, they'll be caught easily.


look inside the tank with a dental mirror and a flashlight at the top surface too. but if it is clean, call it good.



-dan

[dennislarock]

Yeah... I'm with you. I cannot see any rust at all. I've got better than 3/4 of a tank in the car so it'll be a few days (maybe a week) before I do the job. When I'm ready I'll get another gallon or two of acetone and rinse it out a couple more times just before I install the *new* tank.

Thanks!

[DanHoug]

just fyi... i had a horrible black molasses fungal growth in my '83 300SD tank. the only thing that i found that would dissolve it was spray carb cleaner or acetone. ended up soaking the interior for about 2 weeks, shaking it daily while i did other stuff, with a gallon of acetone and it came out well.


-dan

[dennislarock]

Thanks... I'll put some acetone in tomorrow.

Do you know if it was all over the inside of the tank or just on the bottom? I know there can be confusion on whether it is an actual fungus or a paraffin slimy/waxy substance (old diesel fuel breaking down). I've seen both... can't tell the difference other than the paraffin will tend to be on the bottom and the fungus can be anywhere or all over the interior of the tank. The paraffin sludge is by far the more common.

[DanHoug]

it was the strangest stuff... had about 1/2 gallon of this black, molasses amboid mass that slid out the fuel outlet when i removed the screen. most solvents wouldn't touch it including gasoline. then on the inside there was black goo splotches on the walls plus it was all gummed up inside the level sender with the same stuff.



it's so nice now with a clean tank. pre-filter stays sparkly clear. i dose it with a fungicide periodically just to kill any remants in the system.



-dan

[Demothen]

So I just used the POR-15 fuel tank sealer kit for my Spitfire’s 10 gallon tank. The car’s not back in service yet so I cant attest to long term results, but it seemed to work really well, though it was a massive pain. My tank was really rusty, so I set it up as an electrolysis rig for 48hrs first, and degreased it way more than the kit called for. I’m pretty impressed by the results, the coating seems pretty tough, the can built up a 1/4” thick layer of cured material on top after i drained the excess. I’m planning on doing the same thing to my 300D at some point soon, because i’ve had a lot of rust problems in the tank.

[dennislarock]

Yup... POR-15 and Red-Koat seem to be the DIYers go to on this.

Dosed it again this morning with Acetone... rolled, shook and danced with it throughout the day ...will drain in the morning. I closely examined the tank and it looked like the rubber mounts on the bottom had been replaced... i.e., they were held in place by black silicone (not the yellow/brown gummy stuff that MB used) so I called the PO. Sure enough he had the tank cleaned a year or two before I bought the car (not rust... but, the same thing dan experienced). The car was like off the showroom floor... my wife totaled it in a week. It's been a garaged parts car (fuel tank empty) ever since.

So, I'll dose it one more time tomorrow and install on Friday.