New fuel tank for '84 300D? Too much?
 

I mentioned this in another thread but it's more or less dead.

My car sat for about two years before being sold. Family was aged and dysfunctional from what I can gather. Major rust in my primary filter. Hard gritty bits, not likely to be merely bio growth. Not driving it until I deal with it.

Tank metal can't be all that thick. At what point is it better to just replace it?

https://i.postimg.cc/fTYR8xBW/IMG-2725.jpg

https://i.postimg.cc/RZ9VyND7/IMG-2727.jpg

Why not just pull the tank and pressure wash it?

Dkr.

Could be that’s all that’s needed. I have no experience pulling a tank. I imagine I can get it done, what I don’t know is if tanks go over the hill and are not worth saving. Clearly this tank has been doing some rusting. Surely there must be cases of tanks being so far gone you can put your thumb through them or nearly so.

Ahh..the fuel tank herpes.If you are seeing rust,the lining in the tank is gone.You will probably be better off replacing it.

an alternative - POR 15 makes an epoxy fuel tank liner product. obviously you have to pull, wash, line and re-install but it will kill your issues dead. its meant to seal pin-hole leaks as well where the metal has corroded through - i had pinhole leaks.

my application has lasted more than 10 years and my filters look brand new after 10k miles. other than draining the tank and taking a bit of a diesel shower, its really not the worst job to pull the tank. its easier than it sounds and seems.

Did you do the biocide treatment?

IN all the old benzes I have had experience with I have not ever had rust as a problem.

I have seen internal tank rusting on occasion. It was not that common though. There is a slight chance that someone put some sand or something in the tank. Again rare but kids do strange things sometimes.


I would pull the tank and clean it out to inspect it before deciding anything. I was having a little difficulty with what you have getting through the tank filter to start with. The physical size is too large.


It is almost like the rear rubber fuel line is internally deteriorating. Or the one feeding into the primary filter.

Be careful doing this, I don't know about the w123s but on the r107s and even some Porsches the swirl pot that is inside these is made of Bakelite. That epoxy reasin doesn't adhere correctly and will flake eventually.

OP, drop the tank and take it to a radiator shop for a boiling. They should also be able to coat the interior but I would check the inside for a swirl pot and maybe skip the coating. Personally, I think it's unneccessary as gas/diesel will prevent rusting .

These are now 30+ year old cars. I wouldn't be surprised to see 30 years of grit build up.The stuff you see isn't rust but probably detrius from the surrounding environment. In socal it's sand, back east it was a weird mud.

I could have sworn diesel tank herpes was curable with an application of marine biocide. Is that product still around?

I have a lovely tank from an 83 240d. It would bolt in but is only about 17 gal vs 20 for the 300.

Good to know. I'm thinking to take it out and have it checked out and go from there. A bit silly to buy a tank in advance. I was mistaken on the $300 unit. Wrong car. Looks like $500 is more like it.

OTOH, having a new in tank strainer on hand seems like a prudent move.

I haven't used biocide. The detritus looks like rust residue and has hard grittiness. If it is sand, there's a lot of it and removing and cleaning the tank as a minimum seems in order.

This car sat for 2 years. The story they told me at the indie garage/used car lot was that the woman inheritied it from her OP parents who were going into a nursing home. Her husband was being an ass about something and really liked driving the Benz - to F with him she opened the hood and disconnected some wires which he and others hadn't been able to find. The guy at the Indie place says he found it - was something in the glow plug circuit. Odd story, but life is odd. It runs pretty well after the filter is cleaned. I'm going to do the valves and check compression this week. It uses very little oil. I'm hoping this might be a sign of decent compression.

I gather that a somewhat empty tank will tend to rust over that time.

Good to know, I'll examine the tank and see. 17 gal is not bad.

Pull the first aid kit and the sending unit under it to inspect the tank. If it looks ok, leave it in place, pull the strainer in the bottom from under the car, flush the tank, use an algaecide and you should be good.

Replacing the tank isn't technical, bolts, nuts hoses and messy fuel.
WEAR GLOVES AND EYE PROTECTION!

Good luck!!!

Are you saying that flushing it while still in the car is doable? I was wondering about that. One could use soap and water and some pressure and then feed warm air into it for an hour for thorough drying.

I think if you put diesel fuel in and sloshed it around you could get most of the crud out if the large strainer nut was removed from the bottom of the tank.. I would not use soap and water, probably isn't effective and better to keep moisture away. The large strainer should be cleaned anyway with how the primary looks.

Good luck!!!