Fuel Sender working as it should

After replacing the fuel sender, my fuel gauge needle no longer fluctuates (it did when my tank is nearing empty) and now reads accurately. The Reserve Fuel light indicator just went on indicating that I have about 10 liters left in my tank, with confidence.

[BoostnBenz]

Was the old one nasty with gook or do you think it was just "wore out?" I have the same problem.

Originally posted by BoostnBenz
Was the old one nasty with gook ...

Absolutely. And the copper wire was broken. A pricey part to replace but necessary.

[Mike123]

My gauge quick working and when I pulled the sending unit I found it full of gunk,also, and the copper wire was off at the bottom.

I took it apart and cleaned it up. Then I resoldered the copper wire. It has been working properly for the last 35,000 miles since then. I certainly hope it continues. Since I repaired it I have found other instances on this board of others doing the same thing.

[erubin]

When i first bought my '82 300D I assumed i had a problem with my sending unit because the reserve light would go on after only burning about 16 gallons from topped off. The tank is 21.1 gallons (including the 2.8 reserve) per the owner's manual . This meant it still had 5 gallons when the reserve light went on. I dissasembled and cleaned the sending unit even though it was already very clean. After putting it back in it continued to operate the same. I bit the bullet and bought a new sending unit hoping that would fix things but it acts identical. I guess the reserve on my car goes on really early with a quater of a tank remaining. The reserve is like a switch so changing the gauge will do nothing. No big deal for me but since it's my wife's daily driver and she panics when that light goes on I will just have to live with an effective 16 gallon tank.

21.1gal = 80 liter tank
2.8gal =10.5 liter reserve
5gal = 19 liter my reserve

Originally posted by erubin
... I bit the bullet and bought a new sending unit hoping that would fix things but it acts identical....

Possible defective new sending unit?

[erubin]

The new (and old) sending unit in my car are not defective. I wonder if it could be one of the following:
1. My car was meant to have a big reserve. It's an '82 (W123-133-12-001366 ). I think that makes it an early produced car for the 300DT production run.
2. The tank is too deep. I see no physical clues that it was changed and a search on the Vin # at the dealer shows no record of a tank replacement or recall.
3. The sending unit is too short by an inch or two. I have checked the P/N on my sending unit at several sources an it checks out OK for an '82 300D Turbo. The TD and SD use a different one and the 240D calls for two different sending units depending on the Vin in '82. I wonder if any of them would fit and are an inch or two longer.

I give up.

If the vent to outside becomes occluded, I have seen tanks collapsed by 15-20% with no really obvious signs of distortion, and one to nearly half it's rated capacity (but IT looked collapsed). When the occlusion was removed the tanks did NOT return to the original size. At least one was returned to it's original capacity with pressure.

Marshall

[erubin]

Last night I had to drain my tank through the strainer hose at the bottom. This allowed me to fill a completely empty tank. I topped it off to about 5" of the fill opening on level ground. It took 20.7gallons which is just off the 21.1 the owner's manual states. Before filling it up a mile away from home I put 5 gallons in the empty tank and the reserve light stayed on the entire 1 mile drive to the pump. What a mystery.

[240-diesel]

I have had the light come on and then the fuel guage starts jumping up and down , this happens when it is down to 3 to 4 gallons in the tank. It has been doing this for two years approx, I have assumed that when the low fuel light comes on I can get at least 50 to 75 miles until I have to refill . I would like to see if it needs some thing done with the sending unit but after reading what others have done , it seems like a mystery for now and I figure its doing a decent fuel level reading considering you should not even let the fuel level go down that low anyhow. I have been getting 28 miles to the gallon no complaints here.

[BoostnBenz]

Unfortunately since winter is coming I figured now would be a good time to clean whatever out of the tank, so in my last few tanks I've ran it right down to R. I'm very suprised that when the needle was holding on R that I could only get a little over 16gallons in. How far does the needle go down?!? The reserve light surely didn't come on yet, but the light does work. I've double grounded the dash, and put die-electric grease on both sides so I guess now it is down to the sender unit itself....

[erubin]

84W123DT,

In my post i indicated both the tank size and reserve for the 300D:

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You have not run your level down low enough to get the reserve light to go on. Nonetheless, if you suspect a problem it is real easy to pull out the sending unit, disassemble, clean it and inspect that the slide wires are OK. The hardest part is getting a large socket to fit the sender (located under the first aid kit). The socket is something like 32mm (do a search and you'll find the exact size) or just measure it. Before putting it back test the unit out of the tank and see how your fuel gauge reacts as you slide the float up and down. If the slide wires are broken you need a new sending unit, they cost a little over $50.

You could also check that your dash reserve light and wiring are OK by grounding the correct wire that is plugged to the top of the sender. To do this you don't need to remove the sender (only need to unscrew the first aid kit housing).

If you do pull out the sender do it when your tank is real low and get rags ready to catch the diesel that drips off the sender when you pull it out.

If only someone could guess why my reserve light goes on with 5 gallons still in the tank. It should go on with 2.8gallons per the manual.

[autobahnfahrer]

Where would I buy a new sending unit? (W123). The dealer, or are there some quality aftermarket productions?

[BoostnBenz]

Ok, now it all makes sense. It never hit me that the first aid box it right above the sender, I keep hearing about how easy it is to take out but I couldn't see how it came out... until now. They are quite a bit more than $50, cheapest online parts place has $90, it retails at $147.

Originally posted by BoostnBenz
... They are quite a bit more than $50, cheapest online parts place has $90, it retails at $147.

German Start online catalog shows $89