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Thread: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

  1. #1
    E500E Guru RicardoD's Avatar
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    HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    I have a fluctuating / flickering fuel gauge in my car when I got to 3/4 tank and below. Short video of that is here:


    If was able to fix this problem by removing and cleaning the fuel tank sender.


    Screen Shot 2018-10-22 at 8.33.34 PM.png

    Sender part number: 124 542 03 04 (did NOT need to buy, only remove and clean, its over $100 now)

    Parts Required for this HOW-TO (the o-rings for the sender large holder nut)
    Large O-ring: 010-997-81-48
    Small O-ring: 010-997-80-48

    Special Tools Required:
    - 46mm socket. I bought one called a BikeMaster Fork Cap Nut Socket (46mm) from Amazon for $24 It can be used with a 1/2" drive ratchet (many others required 3/4" driver ratchet, I don't have one of those)
    51oQg06Wx7L._SL1005_.jpg


    I created this HOW-To by first referencing this excellent DIY at this link and creating my own photos of the procedure below specific to the E500E: http://www.peachparts.com/shopforum/...g-testing.html

    Drive car until fuel tank is below 1/4 full. I was about 1/8 full. Do NOT do this with a full tank!

    0) Open trunk and disconnect battery.
    1) The fuel sender can be easily accessed from the trunk of you car.
    2) Remover the back wall trunk liner from your car and there are two of those black interior trim clips that need to be removed. Use your interior pry tools to remove the center plunger and remove the clip.
    IMG_1517.jpg

    3) The sender is now visible in the top center of the tank.
    IMG_1480.jpg

    4) The connector can be removed by pulling it off. No secret trick.

    IMG_1482.JPG

    5) Used your 46mm socket to loosen the larger sender holder nut. Then remove nut by hand.

    IMG_1484.JPG

    6) The fuel level sender then easily lifts up and out of the tank.

    IMG_1485.JPG

    7. You may have to clean the bottom black cap with brake parts cleaner to reveal the tiny nut underneath. Mine was gummed up with black gunk.
    bottomcap.jpgIMG_1492.JPG

    8) Now you need a slotted flat blade screw driver to underscrew large sender tube bottom plate. Lucky for me I have a wonderful Boxer "Security Bit' driver set that comes in handy for all kinds of odd jobs. A tiny pair of needle nose pliers may also work.
    IMG_1509.JPGIMG_1493.jpgIMG_1495.JPG
    Last edited by RicardoD; 4 Weeks Ago at 08:46 PM.
    RicardoD
    1990 964 C4 / 1991 964 C2 tip
    1994 E500
    1991 560SEC
    2014 E350 for wife

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  3. #2
    E500E Guru RicardoD's Avatar
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    9)I used electrical contact cleaner to service the sender float and the critical electrical contacts that I believe were the source of my flickering. The resistance of the sender varies from zero (tank full, float at top of sender) to a higher value (didn't measure) at bottom of sender. The low fuel switch is "open" (infinite resistance) when it gets all the way to the bottom and hits the contact points there. Just spray and clean everything. Photos below are after cleaning. I believe the flickering is because gunk must build up on the contact points that slide along the wires (or on the wires themselves) and cause the resistance to fluctuate.

    Basically just clean everything and make sure the float slides up and down smoothly.

    IMG_1501.JPGIMG_1503.jpgIMG_1502.jpgIMG_1500.jpg

    10) you should also clean and replace the o-rings on the sender hold down nut. I also coated my O-rings with Molycote 55.

    IMG_1507.jpgIMG_1511.JPG

    11) Re-install the sender tube and bottom nut. And reverse sender removal procedure to re-install in your car.

    12) I put 11 more gallons of fuel in my tank to put it back to the most common flickering point and so far steady as a rock! Flickering is gone!
    Last edited by RicardoD; 4 Weeks Ago at 08:30 PM.
    RicardoD
    1990 964 C4 / 1991 964 C2 tip
    1994 E500
    1991 560SEC
    2014 E350 for wife

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  5. #3
    Senior Member LWB250's Avatar
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    Looks good so far. Some things I would add:

    Try to do this with the tank as close to empty as possible. I say that because the sender tube will be full of fuel to the height that it is in the tank. The fuel drains out through a little hole that's in that black plastic disc on the bottom of the sender tube, and very slowly. If you withdraw the sender from the tank immediately after loosening it, you will be guaranteed to get a bath in fuel. Once the sender is loosened from the tank, lift it out of the tank a few inches and allow the fuel in it to drain out of the sender. This can take a good minute, so be patient. If you listen closely you will hear the fuel draining out and when it stops. At that point, carefully remove the sender from the tank and have a shop rag in hand to cover the bottom of it to prevent fuel dripping on you or in the trunk.

    I also like to use the sender cover as a plug with the sender withdrawn, so the opening in the tank is not exposed.

    Pay close attention to the alignment of the nichrome wires in the float assembly. Although it's not easy to see in picture #4, the wires actually pass through several guides on the float. If the sender is handled roughly, or the float is moved around by hand without care, these wires can be moved out of the guide(s). This behavior will manifest itself as the float not going all the way to the top or bottom of the travel. With the sender assembled you should be able to turn it over and the float should slide to the end of the travel and be heard to hit the end of the sender assembly. If it doesn't, the wires could be out of alignment. If they are it's a simple matter of carefully moving them back into the correct alignment between the "fingers" on the float assembly.

    Lastly, one area that was not addressed above is cleaning of the bottom cover. When you remove the center nut and the black plastic cover comes off, be sure to inspect it closely and make sure the bleed hole is not obstructed with dirt. If it is, use a pick or small piece of wire to clean it out.

    Dan
    Last edited by LWB250; 4 Weeks Ago at 08:42 PM.

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  7. #4
    E500E Guru RicardoD's Avatar
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    Excellent points Dan. Thanks for improving my write up.
    RicardoD
    1990 964 C4 / 1991 964 C2 tip
    1994 E500
    1991 560SEC
    2014 E350 for wife

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  9. #5
    Member mercedesbenz911's Avatar
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    Great write-up Ricardo and very timely!

    Is the sending unit still accessed from the trunk on non-036 W124 sedans with the 70L tank? Or is it done by removing the first aid kit like W123s?
    1982 280SL
    1994 E420
    1998 540i/6

  10. #6
    Senior Member LWB250's Avatar
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    I have to do this on a diesel W124 in the next day or two - I'll see if I can get some close up pictures of the wire guides on the float. Nice job!

    Dan

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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    Fantastic writeup - thanks, Ricardo!

    If you trust that the reserve light is accurate, you can drive until the reserve light comes on (~3.5 gal remaining) and then drive another 20-30 miles to reduce the amount of fuel in the tank to ~2 gallons or so. Just make sure you have a gas station reasonably close by, or a Gerry-can with premium to get you to there afterwards. No, running the tank that low does not hurt anything. I recommend the same procedure when servicing the fuel filter or pumps; the least amount of fuel in the tank is always safest.

    Dave M.
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    Quote Originally Posted by mercedesbenz911 View Post
    Great write-up Ricardo and very timely!

    Is the sending unit still accessed from the trunk on non-036 W124 sedans with the 70L tank? Or is it done by removing the first aid kit like W123s?
    It is the same for all W124s -- accessed from inside the trunk.

    Nice work on the write-up !! Very high quality and well-becoming of a 500Eboard HOW-TO write-up !!


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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    RicardoD...thank you so much for this post.Very nice job and very nice pictures.Love it
    1992 w124 500e "Blackbeauty"
    1989 w201 190e 2.5-16 Evo spec "Evoltwin"
    2003 Ford Focus Rs (Sold )

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    E500E Guru Trae's Avatar
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    This is timely. . . I need to do this on two of my cars.

    My plan is to use the trip odometer to burn the fuel in the tanks by driving 390 miles before doing the job. Should be very close to empty based on 16mpg.

    Thanks!
    Trae
    1992 500E Renntech
    1993 500E
    1990 560SEC/ 2001 SL500
    1991 560SEC ECE/1995 E320 Cabriolet

  16. #11
    .036 Hoonigan™
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    Quote Originally Posted by Trae View Post
    This is timely. . . I need to do this on two of my cars. My plan is to use the trip odometer to burn the fuel in the tanks by driving 390 miles before doing the job. Should be very close to empty based on 16mpg.
    Trae, the reserve light contacts are separate from the level sensor... so even if the gauge display is wonky, the reserve light MAY still work ok.

    Assuming 22 gallons used (~1.5 remaining) at 16mpg (typical city/mixed driving), that's ±352 miles. You may run out shooting for 390 unless it's all highway (where 20+mpg is possible). Wouldn't hurt to bring a small fuel jug during the last bit of the trips, just in case!


  17. #12
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    Great write up, Ricardo. Thanks for the time and effort.

  18. #13
    E500E Guru Trae's Avatar
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    Whoops thanks for the correction for some reason I was using 26 gallons.

    Is our tank 23 gallons?
    Last edited by Trae; 3 Weeks Ago at 12:22 PM.
    Trae
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    1993 500E
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    1991 560SEC ECE/1995 E320 Cabriolet

  19. #14
    E500E Guru nocfn's Avatar
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    I fill up the 036 at 265 miles and 230 on the 126.
    1994 E500
    249/275 - 8F19 or 8F32 or 8320

    1991 560 SEC
    199/268
    2014 E350 Cab 799/264

  20. #15
    .036 Hoonigan™
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    Re: HOW-TO: Fuel Sender Removal & Cleaning (fluctuating fuel gauge)

    Quote Originally Posted by Trae View Post
    Whoops thanks for the correction for some reason I was using 26 gallons. Is our tank 23 gallons?
    The 036 tank is 90L, or 23.8 gallons... with 11.5L (3.0 gal) reserve, per the Introduction manual.


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