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!!!

I was thinking water and then the right type of mild acid solution. But you could be right - diesel might be plenty good. One appeal of water is I could train a jet through the sender opening, sort of a poor man's pressure washer.

I'll search the web to see what reports are available.

easy to make a better one,out of fiberglass.coat the old one with wax,brush on gel,then layer with glass matting.repeat at least 5 more times, let harden 2 nights. Cut fiberglass tank in half to to peel away from metal tank.Refiberglass the cut you made.2 more nights then mount. I made 2 250 gal diesel tanks for a boat I fished on.

You really need to try the biocide Carl.

Not a bad idea, in some ways, I'm in a weird place at the moment where I have so much work that buying a new one for just under $500 would take me less time that fabbing one in that manner. If it was an NLA item, that is an attractive idea. I worked at a fiberglass boat factory in my early 20s, I understand the principle but never thought about using the old tank as a plug. Also, one wonders if it would be just enough larger to be a PITA to refit.

most bike tanks are fiber,It would never rot again. Also there might be a overseas dealer of poly fuel tanks

I bought the 1-13/16ths socket, was going to clean it while leaving it in but then I couldn't break the strainer nut loose. The ones I've seen in the vids had a 19mm bolt head welded on somehow because space is tight and now I get it. There isn't room for the socket, the 3/4 to 1/2 adapter, and the head of a socket wrench with the axle shaft in the way. I tried with a vice grips on the adapter, finally got it situated so I could really pull but just would not break free.

So I'm all Eff it, I spent the $40 on the socket, I want to see that strainer so I took the tank out. More thorough job anyway. Wasn't all that tough. The strainer looked remarkably clean.

https://i.postimg.cc/FK4q10gj/IMG-2921.jpg

That's just how it came out - the rusty bits on my finger are from swiping my finger just inside the hole, trying to show two things in one photo. Also much evidence of the same sort of rust seen in the primary filter on the nut on the hose connecting the strainer to the fuel line:

https://i.postimg.cc/KcWmjsKB/IMG-2924.jpg

That didn't clean off all that well, looks to be rusted itself. I'll get a new one.

Looking through the sender hole one can see rust on the bottom of the tank but a seat of the pants examination of the outside of the tank indicates that it's far from seriously weakened. The metal thumps pretty solid.

I have an electric pressure washer, not nearly as strong as the gas powered varieties but it will put out some pressure. So far my searching indicates soap and water followed by an acid bath somewhat stronger that vinegar.

I see no swirl pot inside. I can see the hole where the strainer attaches, this looking through the sender hole. Nothing resembling that. My 325i has one. I might see if I can get a recommend on a service around here that would clean and then coat with some epoxy solution. The objection to an epoxy coating earlier involved a Bakelite coating on the swirl pot.

Apologies, it looks like the w123 tanks didn't come with one. Good to know, because when they get dirty it makes for a pain to get clean.

You're free and clear to get a tank boiling and coating done if you wish. A radiator shop boiling will put those little biobastards into their hot chemical equivalent of hell :)

No apology needed, that's good information to know.

Ooo, the hot chemical equivalent of hell. Sounds like the ticket.

Edit: crap, the radiator shop a good mechanic I know recommended can't do it for two weeks.

I found another place who can have it in a week, they recommended a new tank as they want $595. Pelican has a new one for $462, possibly free shipping, +tax about $500.
Might do it myself. I figure pressure wash, some kind of medium acid followed by baking soda fun, followed by more pressure washing. I have an old shop vac dedicated to wet vac, hasn't seen dust in ages, I'll run the exhaust port into that with my heat gun aimed at the vacuum intake, maybe 6 inches away. wouldn't want to melt the sucker.

Found a good guide here:

How to: Clean Rust from a Fuel Tank (using Phosphoric Acid) - XJRider.com

I've restored four rusty fuel tanks, to date, and have honed a process which works quite well:

1. Drain the fuel tank and make sure all traces of gasoline (petrol) are out of it.

2. Remove the petcock and fuel cap.

3. Seal the petcock hole so the tank will hold liquid. I've found that a small piece of wood (about the thickness of a ruler) works well, held in place with the petcock screws.

4. Go to Wal Mart and buy a gallon of Castrol's Super Clean degreaser. Pour half of that gallon into the empty tank and let it sit for about an hour. This will clean out any gunked fuel and will allow the acid to dissolve the rust.

5. Rinse the tank and verify that any/all gunk is out of it. If there are still signs of stale fuel, pour in the second half of the Super Clean degreaser and repeat.

6. Rinse the tank again and ensure that all of the degreaser (and it's foam) are removed.

7. Go to Home Depot and buy a gallon of Phosphoric Acid. It's green and sells as metal Etch and Prep. You'll find it in their paint department. The phosphoric acid will remove any remaining fuel varnish and will also remove the rust inside the tank.

A good used tank should be not too hard to locate. Whatever has happened to your tank was not that typical. As I thought about it. Someone may have removed and cleaned this tank before but used something like a strong acid. Somehow the protective layer on the steel the tank is fabricated with has gotten breeched. Or the steel the tank was made from had a very poor protective coating applied at the rolling factory.

You should have a pick and pull locally. As one option. I would do a quick cleaning and then an inspection of your old tank first. Five hundred when these tanks should almost still be a dime a dozen is somewhat strange.

Rusty Fuel Tank Service
 

I've been tying to help you but you keep ignoring my advice on this...

It's a simple if laborious job .

Clean the tank well using the purple industrial de greasers sold every where, I like to toss in a hand full of sharp edged small flat washers, BB's or pea gravel, then fill it about 1/2 full of the de-greaser and water, button it up and shake the bejeebers out of it, remembering to invert it as lots of rust will be in the upper reaches of the tank .

Drain through a large funnel lined with felt and use the strained liquid to re wash it and get more crud out then rinse clean with water and re fill 1/2 way with a dilute mix of Phosphoric or Oxalic acid and water, the dilute mix should be one gallon acid to three gallons water, add the acid to the water, not the other way round for safety reasons .

Use the small sharp edged items with the de rusing agent too, it'll speed up the job and make it better .

Don't use vinegar it will cause flash rusting .

Phosphoric acid leaves a thin coating .

W123 tanks have NO COATING from the factory .

Phosphoric and Oxalic acids are sold cheaply in gallons at big box hardware stores, look in the flooring department .

Sometimes the self service yards don't punch holes in the fuel tanks, this means you get one for about $35 .

I bought the correct 21 gallon tank from a Mercedes Specific junk yard for $100 and was happy with that price, hardly anyone ever buys used fuel tanks .

If you buy a used tank, mind when they remove it as it's very easy to bend the neck when pulling it out .

Only the M-B original fuel tank filler neck grommet will resist Diesel fuel, all the others will dissolve in less than a year .

The in tank strainer is cheap from any junkyard, I'm sure you know there's an LKQ just down the road from you (South) they get lots f W123's in all the time .

The best filler cap gasket is blue, it's available from the M-B Classic Center along with the filler neck grommet and some 7MM fuel hose you'll want to replace at the same time , leading from the tan to the chassis .

Simply peel off the thin sheet metal crimped collar holding the old hose on and it'll pull right off revealing a standard hose barb .

Be sure to use the correct band typ of fuel hose clamp, a # 12 or 13 .

This is all do able easily at home, it sounds like you stumbled onto a jewel in the rough .

Biocide is important, you should use it periodically as a prophylactic measure, not wait for the clear plastic intake screen to clog .

Remember to order in a spare secondary spin on filter too .

In a pinch you can use the in tank screen from a gasser, it has finer mesh though .

I strain re re use the dilute acid mix for years ~ it's handy to de rust parts and hardwre, nothing alloy nor pot metal but all ferrous metals and brass / copper meaning it's handy for vintage carby jets and contacts from unobtanium switches....

Good luck with this, please keep us informed .

Craigslist usually had kids running impromptu junk yards out of their back yards, maybe look there to find the cheapest tank, it should come complete with sender, yours is going to need disassembly and cleaning anyway .

I'm running into the same thing with W123 that I did with BMW E30s. Wrecking yards always had them in the Oh-Ohs but now it's rare. There is a good looking '83 300cdt in Oakland. However, I just looked at their part price page and they include (may be punctured). I've seen that, they puncture them for quick draining. Have also seen it on oil pans, that a bit whack as removing the plug not tough.

Good advice! I'll study it.

I've read about the gravel idea elsewhere. I have some onhand that has the relatively sharp edges.

I never realized that the 123 tanks where fabricated from uncoated steel. It seemed that Honda four wheeler tanks would so easily rust through from the inside years ago. I suspected almost no protective coating.


Early gas tanks seemed to be fabricated from hot dipped metal being applied. Then possibly electroplated coatings where used. Tern steel was the common term for the sheet steel gas tanks where made from.


I ran across GMs internal cost to make a fuel tank years ago. Possibly in the 1980s. It was about eight dollars in total. This would not include the gauge I imagine.


On a really old gas tank. Sometimes dried gas residue can resemble rust.

Cruddy / Rusty Fuel Tanks
 

Because I work on a large percentage of older vehicles I have way more experience with cruddy and rusty tanks than I wish I did .

The shaking with 'scrapers' inside is really important ~ shake until your arms are falling off then shake some more, I like to shake side to side as well as rotate .

It's a simple if arduous task .

I do Motocycle tanks too .

I work on a tight budget so I've never tried "Evapo Rust" , many Mechanics and Motocycle restorers I know tell me it's the shiznit because it works so well and won't damage the exterior paint .

Oddly enough, when you do a parts search on Pelican, no fuel tank for the 300D comes up, but when you do a Google search, the following comes up:

https://www.pelicanparts.com/More_Info/1074704501.htm?pn=107-470-45-01-M350&gclid=EAIaIQobChMI-6WF0c755QIVMR-tBh3O1wm6EAQYASABEgI05_D_BwE

I was told on the phone that they don’t have it in stock, that maybe it could be procured, 2 to 3 weeks out.

Weird, I was about ready to buy one and go the deluxe, labor saving route.

I’m going to rent one of those mechanical bulls, and strap it on the saddle.

:)

I desperately want to see a video of this.

Fuel Tank
 

....That's a W107 tank.....

I once posted on a Blue Collar Motocycle group about wrapping a motocycle tank in a blanket (or whatever) then tumbling it in the dryer of 'fluff' (cold air) with the dilute mix, you'd thought I'd dropped a bomb from all the nasty insults that began flying 'round....

A couple years later some guys who'd tried my methods before posted that they'd done just this dryer deal when SWMBO was gone for the day and it worked perfectly and didn't scratch the paint .

The electric bull sounds like a fun idea....

It’s a fun idea, and I would love to actually have a video to post but short of having a friend who owns one and would loan it to me, I’m afraid it probably won’t happen.

But you know what? I’m going to do a web search just for the heck of it.

Ah, right you are. It comes up when you enter '300D, W123 fuel tank' in the search box, I could have sworn I saw all of that on the link but looking closer I see in faint letters the actual models it fits.

You can rent electric bulls but they don't give the price. 'Call for quote.'

"Hello, I want to strap a possibly sealed fuel tank filled with various chemicals and hard core solvents to the back of your multi thousand dollar investment and slosh it around a bit, what do you say?"

Oh man, I would love to have access to one of those dry ice powder sand blasting machines. Even a regular old sand blaster would be acceptable. Could get the sand out with pressure washer and wet vac like I did with the rust and gravel residue. I taped a 3/4 piece of PVC about 18 inches into the end of the vacuum hose, worked great.

There are some spots at the top of the tank that are weird. Several small looking vent lines, more busy than anything on the outside. Would love to be able to take a wire brush to them. Might do that - attach one of those small ones to some sort of wand.

I have swapped mine 300D tank to a bigger one from a 280E. Works good. Fungus gone

Whoa. It must fit, or did you have to do significant surgery? I’ll search it later when I have more time, but are they available new? It’s looking like the stock W123 300D tank is hard to get new at this time.

Tank Cleaning
 

? Why the sudden need to buy a brandy new non wear part ? .

You've been told how to easily clean it or where to get a cheap good used one .

FWIW, blasting isn't good for cleaning fuel tanks, it never quite reaches all the crevices .

Is it known that the gasser tank is larger than the diesel tank ? .

Shouldn't need any mods to make fit, just thicker fore and aft dimensions will do the trick .

I doubt there is much difference between the 280e and the 300d tank. I don't know what they are made of but I doubt they are bare steel inside. I imagine they are cad plated. I have never had trouble with rust in any of the 40 or so old benzos tanks I have owned.

Just buy a used one they don't have fungus. Just in case open the leveller to see if there is no rust.

1:1 fit no adjustment welding or cutting.


https://imagizer.imageshack.com/v2/8...921/ByWgzN.jpg

Good point, I've sobered up on that point.

I wasn't thinking that blasting would get all of the tank. There are some thin metal rods running lengthwise at the top of the tank that have small cankors of rust all over them. I didn't try to take a pic - the tank is back in now.

I'm baffled as to what those are. They seem to tiny to have any venting function, about an eighth inch diameter, much less that the external vent line.

I tried to fab a wire brush extender to get in and do a job on them with only a small amount of luck. Coming up with an effective tool for that would just take too much time.

I got quite a bit of rusty detritus out with the gravel. Not sure how much was already loose in the tank. At this point I'm going to watch the primary filter. I'm pretty sure I made good progress. I have bigger fish to fry at the moment.

I'll keep an eye out for a tank, but like I said - W123s are not common at boneyards these days. There is that good looking CDT, I'll give it a look. Almost looks too good to be at a boneyard. I want to be a magician and drop an OM603 into it:

https://www.picknpull.com/vehicle_details.aspx?VIN=WDBAB53A7DB003003

https://i.postimg.cc/D0L7d3ZW/123-coupe-Pn-P.jpg

In the air cooled VW world, cleaning tanks out involve cleaners and some kind of abrasive objects. I have used diesel and a length of steel chain to clean tractor tanks. It is flat out work, shaking a bulky tank around. Having teen age boys, I put them to work...

I can see it now, my big business break. I'll buy some beat up bull riding machine and repurpose it as a shaker for old gas tanks. We'll experiment with different types of abrasive fill - different sized aggregate. Maybe turn the tank 30 degrees every 15 minutes.

Cheap Fuel Tanks
 

O.K., back to the O.P. :

There's one right near you, why not go buy it ? .

If there's any holes punched in it, take it directly to the local indie muffler shop in your Barrio and have the Mexican guy there weld it up ~ he'll have the knowledge and practice to do it plus it shouldn't be over $35 ~ $50 .

Any W123 fuel tank will suit, the 300D's are slightly larger than the 240D's are but bolt right in .

If there's any rust left on the inside vent tubes it's because you didn't use the correct chemical or you rushed the job .

Don't make this molehill into a mountain .

Keeping an eye on the clear plastic intake sc reen is nice but fine rust silt particles will go right through it and grind your injection pump up plus clog up the injector nozzles .

Fine rust particles have a nasty habit of passing through filters and pumps then joining hands when they get to some part of the fuel delivery system when they'll cause the most mischief .

Your call here .

Lastly, Harbor Freight sells rare earth magnets that are disc shaped and easy to place inside the filler cap and on the nose of the drain plugs for the engine, final drive and so on, they're easy to clean the collected SWARF off of and will scare you the first time you see the accumulated SWARF .

I put on a new spin filter. Hard to imagine large bits getting through that. But your point is well taken, I'll look at that tank on the CDT. Can take out the sender and have a good looksee.

I've got the original tank back in, I'll use it for a while, I have some other pressing repairs going on.

Rusty Tank
 

Just to - day I was salvaging parts off a tired 1979 240D and noticed the fuel tank had NO HOLES PUNCHED .

I grabbed the fuel gauge sender, there's some fungus build up in it, but I know how to clean them .

It turns out that soaking them in purple de greaser saturates the composite float dammit .

LKQ raised the sender price, it used to be $16, now it's $22 .

Still a bargain .

Keep us posted .

I have cleaned a W123 tank before and have cut one open to look inside. W123 tanks are quality tanks made from good metals with some kind of Terne coating inside and out that's resistant to rust. https://en.wikipedia.org/wiki/Terne

Here are some recommendations if you are going to clean one:

1. Make sure the vents are not blocked first. Unblock it if it is blocked . Do not use any kind of tank sealers unless you are able to keep the serpentine tank vent tubes from being closed off by the tank sealer.

2. Take the tank out. Mount it to a long pole as if you are doing a pig roast. Support it on 2 forked tree branches driven into the ground. Attach a crank so you can turn it.

3. Put in a few hand full of round beach pebbles or ball bearings that's slightly larger than the vent opening, together with a gallon of good degreaser + hot water (follow recommended product mix ratio), close off tank openings and crank away. It helps to have a borescope so you can look inside for a before and after. Repeat as necessary.

If after the de-greasing, and you still see rust, repeat step 3 with phosphoric acid solution.

Rinse well with water then final rinse with hot water. Dry it off quickly with compressed air, or a leaf blower.

Talk & Fuel Gauge Sender Cleaning
 

LOL ~ I like the idea of putting the tank on a spit and rotaing it .

As it turns out I didn't saturate the composite float in the sender I cleaned ~ it had massive amounts of fungus crud every where and when I cleaned the sliding contacts in the float I moved the delicate hair thin wire out side of them .

I fiddled with it late last night and it's in and working fine .

Time to clean the gooey crud out of the sender I removed again .