What size is the o-ring on the tank screen on my wagon? I've done exhaustive searching and can't find a definitive answer, some results were vague as to if they were wagon or sedan, and some post suggested gas models have a different size o-ring.... All this means one thing to me: Pulling the screen and having the wrong sized o-ring...

The other day I took a closer look at the fuel strainer before the lift pump, it was NASTY. I thought it was ok until I pulled it off and looked closer. Today my car started running really rough and only took 17 gallons at the gas station. I should have a 22 gallon tank. Sooo.... I should probably replace the primary filter and pull the tank strainer. I'm not sure I'll manage in racking up about 350 miles by this weekend (so the tank isn't full...), but I'll do it asap once I get the right sized o-ring.

Splice some 5/16 hose to the tank strainer output and run it into 5 gallon veg oil jugs till empty. Jack up the side of car as high as possible where strainer is closest to before removing strainer. I did it that way on a sedan without spilling a drop or get doused in diesel. Should work the same on a wagon.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I was just gonna put it up on the lift, pull the plug and let it rip into a 20 gallon container... I'm more concerned about getting the right sized o-ring for the screen.

Get the o-ring from the dealer. If not damaged, boil it in hot water for 5 minutes and re-use.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

The parts dept at the dealer up here was rather curt with me when I was looking for the stupid shifter indicator bulb. They almost certainly don't have it anyway, dude told me they stock absolutely no parts for old cars. I'd rather just go to napa and get the right size out of their o-ring index. Interesting on the boiling thing, that works if it's hard as a rock and flattened out? Even so, those are often impossible to get out in one piece... I'm not gonna screw around over a $0.50 cent part I can just go buy.

It's a pretty fat metric o-ring that you may not be able to "just go buy".

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Pelican has one so I'll just buy it from them. I really hope the strainer is all clogged up. If it's clear, I dunno what's going on.... Maybe the supply/return hoses are swapped somewhere between the tank and engine bay? Dunno, maybe I'll find out the tank only has a 17 gallon capacity because it's collapsed or something else is weird, who knows... Only one kinda messy way to find out

I'm not sure if it's the same on a 123 wagon, but I can tell you what causes this problem on 201's and 124's. The filter screen doesn't just screw into the bottom of the tank. It fits into an oddly shaped cup that functions as a baffle. In normal operation, fuel returning to the tank flows through a venturi orifice, which through an oddity of hydraulics draws fuel from the bottom of the tank and fills the cup. It keeps the car from stalling when you are low on fuel. If the bottom of the tank has some muck, the orifice closes up and you only get fuel if the level is above the top of the cup. So you may run out when the gauge indicates 1/4 tank. The attachment may make this more clear.

The only way I've been able to clear this is to drain and remove the tank and have it boiled out at a radiator shop. The root cause may be a bio infestation, but once it reaches this point, you're stuck.

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Hmmmm, I can't find anything that confirms or denies that's how the w123 tank is. I wish it wasn't a pain to pull the fuel sender, that might give a hint as to how dirty the tank is. I have jump seat in my car, and it does't look overly fun to get out.

My fuel gauge reads empty at half a tank, it started doing that after I removed the gauge cluster to fix the odometer.

Splash pot. I have more and more respect for the old MB engineers every time I see something like this - never heard of it before. Did US cars have these?

Never seen it before, but I have an old generator with a Wisconsin engine on it. The engine uses a similar kind of system for the crankcase lubrication, so even if the oil level is low or the engine is on an angle, there's the optimal level of oil for the crank.

That right there, is the reason I have been putting off removing my own gauge cluster to repair my odometer! Too afraid of mucking something else up that was working fine previously! You just reinforced my feelings, LOL.

Have you already tried adding startron or another similar additive to see if that might cure your fuel starvation issues caused by deposits or other grunk on the intake screen?

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2007 Dodge Ram 3500 Cummins Turbo Diesel 4x4
1994 GMC S-15 pickup 4.3 5MT
1985 300 SD
1978 300 CD
1962 220-S Fintail - awaiting restoration

Your best bet would be to go ahead and remove the sending unit, replace the "O" ring too.

The tank strainer does screw in/out. Use a new "O" ring there too.

Pelican Parts - European Automotive Parts and Accessories - Porsche • BMW • Mercedes • Volkswagen • Audi • Saab • Volvo • MINI

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83 SD

84 CD

Yup.

Yea, not even sure what I did wrong... There's one electrical connector to the back of that module, and you don't even have to touch the fuel gauge to get the odo out. You'll also realize your oil pressure gauge leaks a little bit ...

I had like 1/8 tank when I did the job, put it back together and it read full empty, didn't even move when I turned it on... Coincidentally after I filled up that tank of diesel, I never had full capacity again, so I can pretty certainly trace the issue back to that station. Probably got crappy fuel because the car started smoking and shaking at idle not too soon after. A problem which has fixed itself...

Yea, probably should. It just looks like a pain to get the jump seat out so I haven't bothered..