Well this was a surprise.....three draws from the tank and looking into it with a flashlight, I can’t see a damn thing other than fuel! Did notice a few specks of rust from the filler neck which I expected, but no sign of bugs or bacteria.....gonna drop the biobor in anyway and will check again after the weekend.

Would bacteria be isolated in like a little ball or something, or just generally mixed in with the fuel such that I should expect to at least see some trace of it taking fuel samples like this?





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If you could put a weight on the end of the hose to make sure it remained on the bottom of the tank, that might be an interesting way to get a sample from the bottom. And then what would you do if you pulled up some water or some sediment or some evidence of microbial growth?

I'd say there are other ways to get the job done. Pay attention to what you can see in the pre-filter, and use that observation to decide on what actions you need to take. Another sign that you need to take corrective action would be a clogged up main filter.

Biobor or other biocides are intended to poison the fuel and any water in the bottom of the tank, so that microbes (think mold, not bacteria or algae) can't live there. Biocides alone do nothing about the water, they just kill what might be in the water. The microbes live in the water and eat the fuel.

If you're pre-filter has black bits in it, that is a good sign of microbial growth, so kill the little suckers and keep some extra filters on hand to deal with the bodies as they leave the tank.

The easiest way to deal with any water that might be in you tank is by adding a product meant for water problems, like Heet (get the diesel fuel variant). A good practice would be adding Heet to your fuel tank every fall so that it is de-watered for the winter and you won't have a frozen fuel filter or system. Diesel 911 is another product I like, but more expensive and also does other things like treat the fuel to raise the cloud point so you don't get fuel gelling in cold weather. If you use a de-watering product each fall, there will not be anywhere for the microbes to live, so they should no longer be a concern and the rest of your Biobor will sit on the shelf for years.

Water gets into the tank naturally with the heat/cool cycle of each day/night. During the day, any air space in the tank is heated up and air leaves the tank. At night as the tank cools down, cool moist night air is drawn in, and some the humidity condenses out of the air onto the inside of the tank, and then drips down. Water is heavier than diesel fuel, so it goes to the bottom of the tank and collects. If you keep your fuel tank full so there's no air space or very little, you can avoid this. It is a good practice to fill the fuel tank as full as possible if you are going to leave the car sit for an extended period, this will reduce the amount of water that builds up.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

The more extreme methods are removing the tank screen to clean or replace it, or removing the tank to flush and clean it, but the way your car is running now I'd say those options are not worth considering.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Monday I’ll tie a fishing weight in a knot at the end of tubing and see if I can be sure the sample is from the bottom of the tank - that’ll be three full days of biobor while at rest.

I also turned my cell flashlight on and held it underneath my primary filter and believe it or not, it actually appeared quite clear but pretty neon vibrant green like the samples I pulled today.

Also could not for the life of me get my primer pump top to turn left and loosen up for priming...

Have a great weekend everyone and thanks for the guidance!!


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You can easily see into the tank if you remove the fuel sender.
This does require removing the rear bench seat bottom and rear bench seat back.
IIRC you need to remove the three 8mm sheet metal screws to remove the seat back.
You don't need the special wrench (46mm??) to remove the fuel sender, channel lock style pliers work well.

Here is a link to the W123 FSM.
if you'd like an actual physical CD version of the W123 FSM, I can sell you my old one cheaply.
Just shoot me a PM.

BTW what year is your W123 240D?
It can be very helpful for responents if you post that info in your initial postings.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

IIRC the plunger lock is spring loaded.
I believe you must push down firmly with your palm and then twist ccw.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Fuel intake lines, both filters, and hand primer pump replaced after a purge. The purge was not at all what I expected, and the fluid (which I all but used up) stayed nearly clear the entire time even after high revs and under load - so a bit anticlimactic there. The old hand pump was incredibly leaky and broken - long overdue on that one and now I know why I had a nice shiny area in the side of the engine underneath that pump.

I was able to get a second gen fuel filter banjo bolt - but I just replaced my gen 1 o ring and crush washer and it was fine - but will a gen 2 bolt just plug and play in my gen 1 fuel filter body?

Also found primary filter had a decent amount of very hard tiny little black/brown granules - almost exactly like sand but smaller and much darker. After dumping them out on cardboard and letting the fuel evaporate, they were like dust, but definitely hard and not easily able to be crushed into dust. Does that sound like diesel bug or rust in the tank?

Power steering fluid was nearly black and the old filter was in pieces! New ATF in there along with a new filter and will probably change yearly for a couple years while it cleans itself out. Did notice what looked to be like some of the hoses weeping a bit at the ends with the new fluid in there, but we’ll see.


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Thanks Alec! It’s a 1981 4speed 240D - I can get that fuel sender out just by removing the first aid kit, and plan to do so as soon as my body guy is done with his work (the car is taped up and mudded, etc. and I’m limited to just tinkering under the hood for now).


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The "02" hollow bolt with two o-rings will physically fit an "01" fuel filter head but it will not seal well.
Best to get an "02" filter head for the "02" hollow bolt.

Check the grains with a magnet to see if they are rust from the tank.
The black/brown grains are most likely asphaltene precipitates that can cause fuel filter clogging and rough running.
StarTron diesel fuel tank cleaner followed by regular treatment with StarTron diesel fuel conditioner,
or other fuel additives designed to re-disburse asphaltenes (Penray, etc.) can take care of this common problem.

They are readily available at boating/marine supply stores or online.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

So I’ve noticed my 01 banjo bolt definitely leaking. I used an aluminum crush washer but I guess didn’t crank it down hard enough the first time and then torqued it two more times after noticing leaks - I’m sure that just made it worse, right? Do I just take the damn filter off, put a new washer in there and try again? I did replace the single o ring on the bolt too.

What kills me is that I know the PO had no crush washer on there at all and it did not leak! Granted it leaked at the swollen and cracked fuel lines at the clear primary filter and at the faulty original hand primer pump (both of which now don’t leak anymore!), but it not leak at the secondary filter until after I changed it and added the crush washer to the equation.

The large air bubble you guys noted in one of my clear hard plastic lines off the secondary filter did completely go away though and has not come back.


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Part of a serious tune up of the 240d fuel system. Is making sure good fuel pressure exists in the base of the injection pump. At least remove the overflow system pressure regulator return valve from the injection pump. Take it apart and measure the spring. It may need stretching to the original specifications. To restore the right operational pressure.

If nothing else the engine runs better with the correct pressure present. Yours may still be fine. Yet the only way to know is checking things. This car is thirty five years old.

Actually it is ignored in general but Mercedes tune up information for these diesel engines. Is to check the fuel pressure. With a gauge from time to time. At certain millage intervals. This can detect a relief valve getting weak or a lift pump getting weak or a fuel system restriction. The 240ds lift pump is also a lower pressure output version than those used on the turbo engines.

Anyways over time I have found a lot of clues. That indicate to me at least this may be important. Some effects of low injection pump base fuel pressure are well known. One is still highly subjective. My attitude is why ignore it? When it is so simple to make sure it is not a even remote probability.

Barry -re: lift pump differences on the 240D, have you known anyone to replace the 240/na lift pump spring with one meant for the 300 turbo lift pumps? Found a turbo spring online and have been considering.


240Dee- I've also had the black granules in my pre filter for a couple of years now. Haven't caused any issues I've known of, but have been considering a startron treatment myself. Do keep us posted...

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1981 240D 4sp manual. Ivory White.

Woah, good advice - thank you! I did not realize that about the IP spring and I’ll look more into it. There’s also a 300D (turbo) in my local yard that I could grab said spring from so I’m interested to know about that too! Always a pleasure to hear from you folks!!


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From what I understand, there are two springs to consider...

The first, the one that can be stretched to 27mm, is in a banjo bolt on the back of the IP (facing engine, the one with the fuel return line coming out of it).

The second, is within the lift pump itself. I don't think that's one to be stretched, but it can be replaced with a different spring, mainly the one from the lift pumps in the turbo line.

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1981 240D 4sp manual. Ivory White.

I think what you may find is that putting any kind of tube down into your tank through filler will kick up all kinds of stuff that was previously stuck to the inside of the tank - and whatever you extract will be outweighed by the new stuff you release.

I once had to siphon some diesel out of my tank, inserting a hose to do so and knocking it adjacent the bottom/walls of tank - and I've since had so much particulate garbage come through into my pre-filter. Until I get around to dropping and cleaning the tank I've been changing my pre-filter OFTEN to deal with the sludge kicked up.

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Andrew
Montclair, NJ
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1982 300D Turbo
120k
Petrol Blue Green