w123 out of diesel at 1/8 tank
 

I had to drive to upper Westchester for work today. On the way back, I noticed that the car wouldn't idle well, but otherwise ran fine. Got on the Rt. 9 freeway, and the car suddenly lost power and died. I was very lucky, since I managed to exit, roll into a gas station that had diesel, and stop about 3 ft from the pump!

Looked under the hood, and the clear filter was bone dry -- a full tank of diesel and a bit of primer pumping fixed the issue right away! However, the needle was still above the R mark (looked like 1/8 tank) when this happened. No warning light either.

What's going on? Fluky gauge, lift pump, or could the "straw" that sucks diesel out of the bottom of the tank be damaged?

How much fuel did it take when you filled it up afterwards?

It is probably your fuel sending unit. They have an interesting mechanism with a float that travels up and down on wires. They can get stuck and not slide easily, which is why it may have been reading 1/8 when you actually had zero.

But if the fill up quantity suggested that your tank still actually had 1/8 in it, then the problem lies elsewhere.

No idea - I just dumped $50 into it, didn't 100% fill it up.

hard to know for sure, the senders do get gunked up, requiring cleaning/replacement. also, the tank strainer gets gunked up, keeping the last bit of fuel in the tank... if you fill the tank and it only takes 18 or so, then it's a strainer problem, if you get the full 20ish gallons, it's likely the sender.

Back when I had the W-123, the same thing happened at a 1/4 tank. I was on the NJTP and the tripmeter just crossed 500 miles and I'm thinking...........this is almost too good to be true. This vehicle never could go 500 miles on fuel.

It didn't.:mad:

Thankfully, I got a ride to the station (about three miles) and a ride back to the vehicle.

Strangely, it only happened once.

But, I never trust the gauge anymore. The tripmeter rules the day. I'll push the SD all the way out to about 560 miles...........not more.

I had a similar situation that I fixed last night. My sender was never getting the reserve light. I put biocides in the tank drove it around to mix it and let it sit for a couple of days. I then removed the sender and cleaned the wires and the rest of the unit. The copper wire was disconnected and obstructing the float from going lower on the pole and floating to the top when the tank was full. I took a thin wire and wrapped the copper wire as to get the line to connect... I'm not sure the reserve light will work properly with a proper soldering job but as long as the sender reads the gas right, I'm fine with that.

The 123 fuel level senders are notorious for being jumpy and flakey. They get pretty gunked up over the years, and sometimes cleaning them out will fix the issue. But often a 30+ year old sender is a little flakey. A new one will cost you your left nut, right arm, left leg, and your first born. They are $200+ new these days. Mostly likely yours needs some cleaning.

Yes the sensor is cleanable

On 123 sedan it is under the first aid box (2 screws to remove the pan).

Hint: remove bottom back seat cushion (push in buttons lift out) upper back cushion (3 x 10 mm bolts, lift out with a helper) then lay down plastic to protect against drips.

Unplug connector and using either 46mm socket or a pair of channel locks loosen and remove the sensor tube. Pull up a little and wait for it to stop dripping before pulling out all the way...

Now using a pair of snap-ring pliers carefully remove the weird nut at the bottom then remove the bottom plates. Now very carefully slide the mechanism out of the tube. There should be 3 fine wires that are very delicate and a float with contacts that bridge 2 of the wires. The low fuel light is a set of contacts at the bottom, yours might be buried in sludge.

Using mineral spirits and extreme care clean everything. Put it back together and take it back to the car. Plug in the harness with the sender out of the tank and turn the key to pos II without starting it. With the sender held vertical, you should have the pointer on Empty and the low fuel light on. Now slowly turn the sender horizontal and begin slowly turning it past horizontal allowing the float to slide towards the connector end. The needle should rise to full and the reserve light goes out. If it is all good shut the car off, unplug and reinstall.

That's also where I am now, watching the tripmeter. Ran out of fuel for the first time in many years a few nights ago, the fuel gauge was showing between 1/4 and R. However the low fuel light had been on a couple days, that seems to still work well.

I made it 552 miles on a tank in my SD. I drive short distances, stop and go, extremely hilly terrain... I'm thrilled to find out my new-to-me cheap used car is getting around 25MPG. If I wasn't so broke I would have found out exactly how much fuel the tank would have taken from empty (maybe some tank screen clogging going on?).

At least I bought a new autozone battery this month.

With a 20.5 gallon total capacity, you're doing well above 25 mpg unless you manage to drive into the station on the fumes.

I must have been running on fumes when I filled up previously--I thought I put in nearly 21gal. ($93.64/$4.47 ->20.94gal).

Around 26mpg, maybe. I can't wait to watch the fuel efficiency on a longer trip instead of my usual commuting/errands/hilly area (which yields horrible efficiency in most cars).

Something a little closer to on-topic: I read that some people reverse the fuel lines under the hood to find out if their strainer is clogged. You have to do this with over a half tank of fuel because the return line draws from mid-tank.

If the vehicle starts to idle poorly and has very low power when the tank gets below 1/4, but returns to normal performance with a full tank, the strainer is clogged.

If the strainer has never been replaced in the last 25 years, the strainer is clogged.

Where are you getting the 20 gal capacity? AFAIK, the 240D's only had a 17-gal (usable) tank.

Not everybody can stomach a 240D...................

There appears to be some parallel discussions occurring, which may have caused confusion.

To continue that trend, I wanted to emphasize JayBob's post above regarding cleaning the sender. The idea to test the sender outside of the tank is very smart, and something I missed entirely. To test my Reserve light after cleaning my unit (it contained some black/green slime), I kept driving one day until either the Reserve light came on, or I ran out of fuel. I was carrying a spare gallon in the trunk just in case, but testing it outside of the tank would have been a wee bit smarter.