'83 240D - fuel gauge reads 1/4 on full tank

This car sat in a barn for 15 years before I got it last fall. I now have it on the road.

The fuel tank reads a little over 1/4 when the tank is jammed full.

I'm guessing this is the sender in the tank. How hard is it to get to and remove and what is the repair procedure- replace or clean?

Very easy to remove, it is under the first aid kit on the rear deck. It is very very fragile! Be careful and gentle not to break the wires on it. You will understand it when you see it. Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

A couple of links to read through that should be of benefit:

FSM: 1983 240D - Removal and installation of immersion tube transmitter

Fuel Sender 85 300D- Cleaned (Pics)

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

If you find broken wires or rust on the sender, you might take a look at my last post to http://www.peachparts.com/shopforum/diesel-discussion/377979-fuel-tank-sealer-questions.html - though I need to go back and update that with the specs for nichrome wire I used..

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'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild

Sweet! That looks pretty easy.
Thanks!

Yes fairly easy job. A couple hints:

Go ahead and take the back seat out totally, both the cushion and the backrest. If you spill fuel it will soak into the seat and it will make the car smell like fuel. Put down some plastic over the rear deck area in case there are drips.

Unplug and unscrew the sensor (use a 46 mm socket or a big pair of channel locks). Pull it up halfway and wait until you hear it quit dripping (best to do this when the tank is low). Have a shop rag ready to slip underneath as you pull it out.

The bottom nut unscrews. A small pair of snap ring pliers works well to reach into the recesses of the nut to unscrew it. Lay out the parts as they come off the bottom, they will all be caked in goo.

Finally the tube will slide off. Carefully remove the tube from the center stem.

Clean up everything in mineral spirits. Be very careful with the hair thin wires. Be sure to get the slider free from the bottom and clean underneath it.

Put everything back together and bring it to the car. Before inserting the sensor in the tank, plug it in and turn the key to the II position.

(Go under the hood and unplug either connector from your glow plug relay on the left fender before doing any troubleshooting involving the key in II without running the engine, or you have a good possibility of burning out a glow plug. BTDT.)

Anyway with the key on, hold the sensor vertical with the plug at the top. The gauge should read empty and the low fuel light should be on.

Now slowly rotate the sensor so that it is slightly above horizontal. The slider inside should start moving to the top, and the low fuel light should extinguish, and the gauge should rise towards full. If it checks out put it back in the tank.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

I have *mostly* fixed the sender. I took it out and apart, and found that the float was stuck at one point on the shaft. It was all built up with crud.

I got it all cleaned up and cleaned the shaft so it slides up and down easily.

Now, when the tank is full, it shows 3/4 tank. This is fine until it gets down to around the 1/2 tank mark. Then, it starts bouncing a lot between zero and half.

Last time around, once it got to maybe 1/3 or 1/4 tank, the needle just pegged to the left and stayed there.

I think I'm going to have to pull this again and maybe clean the sensor wires with steel wool (delicate job, I know). I also recall the wires being a bit loose and floppy. It seemed like they should have had more tension on them.

In bench testing with an ohmmeter, I found that the reserve contact never got shorted to ground when the float was at the bottom, even after I carefully cleaned all the brass contacts. I ended up having to solder a wire to get continuity between the contact and the sensor wire.

Make sure you have the wires between the contacts of the float on both sides. Looking really closely you should see two chevron shapes. If memory serves you need to have the wire between the points of those two. You need to see >|< ... not <|> or <>|

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'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild