There is another possible answer: PO or someone has accidentally reversed the supply and return lines, either at the tank or at the engine bay. Next time you get the low fuel symptoms, try reversing the fuel lines in the engine bay and see if that solves it. I have read that such a line reversal will cause a low fuel "run out" when the gauge still reads about a 1/4 tank.

__________________
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

They're not reversed in the engine bay, you can't even hook them up wrong, the return line isn't long enough to reach the supply line. I have thought about the possibility of reversal at the tank. I should just remove the lines and blow air through them to see where they come out under the hood.

I dumped some clean-diesel in there today, see if that sends a lot of gunk into the under hood filters. I'm carrying spares and the tools to change them on the side of the road :V

What does your gauge read when you run out of fuel? Does it read at the bottom, or does it indicate the presence of a few gallons of fuel still in the tank?

I had the same issue Maxbumpo speaks of; my fuel lines were reversed at the tank. Tank would "run out" when it was 1/4 full. Switched the lines around and got my full 17 gallons.

One thing to be aware of, though, is the fuel lines can rust in places where they are not readily visible. Mine looked just fine, but they immediately broke above a crossmember in the rear where they had rusted out of sight. It would be good to have some spare hose and fuel line on hand to repair any breaks if you bend the fuel lines under your vehicle.

As I said above, my gauge is screwed up so it's not a good indication of anything. I'm only getting a 17 gallon capacity, manual says it should be about 22. I doubt my lines are rusty, nothing on the car is rusty, it's lived in Florida and Virginia its whole life.

I'd start by getting some pieces of fuel line so that you can reverse them in the engine bay and see if that resolves the issue. Much easier than crawling under the car, and also easy to reverse on the side of the road if my idea is wrong.

__________________
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 only reason I don't want to do that is if the strainer is clogged up causing my issues it will disperse all that debris through the tank. I'd rather just pull the strainer and clean it off.

I had a similar problem. I replaced the strainer and the problem got better, but it's still not great. (In my case there really wasn't all that much crud in the strainer, or the bottom of the tank.)

I think the real problem is the wagon tank is a poor design. It's flat and not very deep. They tried to compensate for this by putting a false bottom in the tank, creating a baffled area under the strainer, but that only holds so much fuel.

Basically the last three to five gallons are not usable if you live in an area with steep hills. On the flat everything's fine, but once you start to climb a hill all the fuel sloshes to the back of the tank. Now you have maybe 20 or 30 seconds of fuel before you've sucked the baffled area dry and the engine starts to slow down. Sometimes if this happens you can coax it a little further by giving the brake a quick stomp, or swerving side to side, to slosh more fuel into the strainer. Or just bang a quick U-turn to go back down the hill.

Unless you live in the Great Plains you may just have to keep it above 1/4 tank.

__________________
1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

Hmmmm interesting. The only time I drive on flat ground is the carwash and the gas station. Maine is one gigantic hill so interesting.

I think this is wrong. I think the cup-shaped baffle is used on the wagon as well, and a blockage of the venturi opening explains the problem. Does anyone have a 123 manual handy?

I looked in the w123 manual online in the fuel tank section and couldn't find any pictures or diagrams of the internal tank workings.

From what I could see there's a double floor, and fuel flows in the top part of the strainer and then out the lower part into the lower chamber. That's why the wagon strainer doesn't have a fuel feed connection. There's an illustration in another thread here: How does the tank screen work on a 123 wagon

I don't know if there's an additional baffle inside the lower chamber.

The sedan tank is very different. It's mostly vertical, so it doesn't have the same sloshing issues.

__________________
1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

I live in the Seattle area, so same deal.

__________________
1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

I can't comment on your problems, but I checked my fsm, and it lists the tank for a 123.193 300TD turbo as having a 70 liter tank, which comes out to not quite 18.5 gallons. This seems consistent with the 84 300TD that I have, as much as I would like to have the 22 gallons of the sedan.

Fwiw.

W.

Here's a pic of a W123 300D sedan tank cut open. I'd think the wagon tank is similar with the strainer and return. The hole at bottom left is for the tank strainer. The nipple at bottom right is the return which protrudes not more than 1/2 inch off the bottom.

The nipple at top middle is the vent (line has been cut because I was trying to clear a clogged vent). Hole at top right is fuel sender. Hole to the left of sender is a hole that I made so ignore that.

__________________
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

Yes, 70 liter tank INCLUDING an 11 liter reserve, that's 21.4 gallons. I was calling it 22 because I'm lazy. The light is supposed to come on when you have 11 liters left, apparently.