How to replace the fuel sender in a
Mercedes Benz 450SE
This procedure assumes that the gas gauge sending unit in a 116 body Mercedes Benz needs to be replaced. Besides having a fire extinguisher nearby, you will need some tools. Most of these are inexpensive and commonly found. One, however, is an unusually large metric socket, and the cost of this tool is high enough to warrant borrowing or renting one.
This procedure involves working with an electrical component that is immersed in gasoline. Extra care must be exercised while performing this procedure.
This procedure involves working with an electrical component that is immersed in gasoline. Extra care must be exercised while performing this procedure:
Absolutely NO SMOKING!! No open flames nearby! Remove the ignition key and disconnect the battery positive terminal! Have an approved fire extinguisher nearby.
I cannot emphasize this enough:
Failure to follow gasoline handling safety procedures can result in property damage, severe injury, or death.
Park the car outside, in the shade, preferably on a cool day. The cooler the car interior is, the better. Leave the doors open during this procedure to insure proper ventilation.
Never work alone. This procedure can be performed by anyone handy with tools by themselves. But, as with any automobile repair, you should have someone with you who can at least call for help should trouble arise.
Read through the entire procedure first. It is recommended that you print it up and have it on hand for the task. Take your time and do a good job. You will be pleased later on that you did.
This procedure assumes that the gas gauge sending unit in a 116 body Mercedes-Benz needs to be replaced. Besides having a fire extinguisher nearby, you will need some tools. Most of the tools are inexpensive and commonly found. One, however is an unusually large metric socket. The cost of this tool is high enough to warrant borrowing or renting one.
You will need the following tools:
BC rated fire extinguisher
#1 Philips screwdriver
Small flat-bladed screwdriver
Safety goggles or glasses
Protective gloves (recommended)
46mm or 1 13/16" socket and breaker bar
Fuel sender unit p/n 116 542 0304
The sender unit is a metal tube with a plastic flange on the top containing 4 metal pins. One is slightly larger than the other 3 and is offset to act as a locator in the connector.
- Disconnect the battery positive terminal and tuck it away from the battery post.
- Open the back doors of the car and get in the back seat, leaving the doors open.
- Put on your safety glasses and protective gloves. Put the fire extinguisher next to you.
Have the tools and the new sender unit with you on the seat.
Replace the nut-ring and start the threads by hand. Be careful not to cross-thread the nut. Tighten it down as far as you can with your fingers.
Access to the sender unit is through the back deck. There is a flap-style door that covers the First Aid kit. open the flap and pull out the First Aid kit. Using the Philips screwdriver, remove the 4 screws holding the First Aid kit plastic well.
Carefully pry the plastic well up with the flat-blade screwdriver. Take your time and avoid cracking the corners and edges. The sender unit is right beneath the well. It is held in by the 46mm nut-ring and has a brown electrical connector coming out of it.
Pry the connector up off the top of the sender using the flat-bladed screwdriver. Be careful not to crack it or pry the back off of it. The back simply snaps on and can easily be replaced. Get out the 46mm (or 1 13/16” ) socket and put it on the nut-ring. Make sure it is properly seated. It is somewhat tight quarters and the nut-ring is very tight. Put your ratchet or bar on and unscrew the nut-ring.
Remove the nut carefully by hand once it is loose. The nut has very fine threads; place it aside where it won’t be damaged or get dirt in the threads.
Gently pry up the old sender from the gas tank using the flat-bladed screwdriver. Be very careful that you do not drop anything into the tank. Remember that gasoline is very flammable and the fumes are explosive and toxic over even a short exposure.
Slowly lift the old sender out. It is partially filled with gasoline; let it drain into the tank for a few minutes before pulling it all the way out. Be careful not to drip gasoline on yourself or the interior of the car. Notice that the sender shown here has a brown sludge/rust deposit on it. There is a good chance that the same stuff is inside and caused the unit to fail.
Insert the new sender. Notice there is a plastic nub on the lower side of the top flange. This lines up with a notch in the top of the gas tank opening. Be sure the sender sets into the opening flat against the rubber gasket.
Tighten the nut-ring down snugly with the socket and bar. I’m not sure what the torque should be on this, but try to match the force needed to remove it. Do not tighten it so much that you strip it!
Put the connector back on. Notice that there is a larger locating pin that goes in the largest hole in the connector. Push the connector on as far as it will go to insure a good contact.
Hook up the positive terminal on the battery and turn on the key to check that the gauge now functions. Turn the key back off and replace the plastic First Aid kit well and its 4 screws.
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