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Fuel Level Sender Replacement
 
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Pelican Technical Article:

Fuel Level Sender Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$240

Talent:

**

Tools:

42mm socket or large wrench or channel locks, Philips head screwdriver

Applicable Models:

Mercedes-Benz 300TD (1979-85)

Parts Required:

Level sending unit, sealing O-ring

Hot Tip:

Be careful working around fuel

Performance Gain:

Knowing how much fuel is in the tank

Complementary Modification:

Replace fuel filter

The fuel level sending unit on the W123's will fail over time. One of the signs that it is going is erratic fuel level readings especially in the lower third of the tank. The units work by measuring the electrical resistance between two wires in the sender. Unfortunately the unit will not last the life of the vehicle. If yours is starting to go, make sure to replace it before you get stuck at the side of the road out of fuel. Our project W123 was a 300TD wagon and the level sender was under the rear compartment; on the sedans it is located in the trunk area behind the rear seats.

It is best but not necessary to replace your level sender with the fuel tank drained. This reduces the amount of possible spilled fuel and fuel vapors. Wear proper clothing, gloves and safety glasses when working with gas. When replacing, work in a well ventilated area, working outdoors is a good choice. Do not use incandescent work lights or power tools and DO NOT smoke as fuel and fuel vapors are highly combustible.

Begin by disconnecting the ground cable from the battery post (red arrow) and placing where it cannot accidentally come in contact with the battery while you are working.
Figure 1

Begin by disconnecting the ground cable from the battery post (red arrow) and placing where it cannot accidentally come in contact with the battery while you are working.

On the wagon the fuel level sender is under the rear compartment; first remove the rear cover (red arrow).
Figure 2

On the wagon the fuel level sender is under the rear compartment; first remove the rear cover (red arrow).

Next remove the cover underneath (red arrow).
Figure 3

Next remove the cover underneath (red arrow).

There should be a series of hold down clips holding the cover in place.
Figure 4

There should be a series of hold down clips holding the cover in place. Use a Philips head screwdriver, remove the hold down clips and the cover will come right out.

Pry off the cap protecting the sender unit (red arrow).
Figure 5

Pry off the cap protecting the sender unit (red arrow).

Using your hand separate the wiring connection from the unit by pulling it straight up.
Figure 6

Using your hand separate the wiring connection from the unit by pulling it straight up.

The nut holding the sending unit in place is very large but it should not be torqued on ridiculously tight; there is a rubber O-ring under the cap that does the sealing.
Figure 7

The nut holding the sending unit in place is very large but it should not be torqued on ridiculously tight; there is a rubber O-ring under the cap that does the sealing. Use a large set of pliers or channel locks and carefully unscrew the unit. If there is dirt or debris around the cap that might fall into the tank once you remove the sender, make sure to clean this first.

Pull the unit out from the tank allowing it to drain as you go.
Figure 8

Pull the unit out from the tank allowing it to drain as you go.

If you are reinstalling the sender always make sure to replace the rubber O-ring (red arrow) as this is what seals the fuel and vapors in the tank.
Figure 9

If you are reinstalling the sender always make sure to replace the rubber O-ring (red arrow) as this is what seals the fuel and vapors in the tank. Installation is the reverse of removal.

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