Results 1 to 11 of 11

Thread: Fuel Gauge Reads Inaccurately Near Empty

  1. #1
    Senior Member LWB250's Avatar
    Join Date
    Feb 2018
    Location
    Tampa, FL
    Posts
    230

    Fuel Gauge Reads Inaccurately or Hangs Near Empty

    This one was a bit of a stumper for me, and something that I probably would never have sorted had I not looked closely at things...

    The complaint: When the fuel level got down to about 1/4 tank or lower, the gauge did not read accurately. That is, the gauge would not move to the reserve position, or if it did, it would occur suddenly such as after driving the car on rough roads. Conversely, when the tank was filled the gauge would read low for a short time after, then suddenly move up to the full position.

    I removed the gauge sender from the tank and inspected it. I found that when I inverted the sender, the float would sometimes hang up near the end of the travel. If I tapped the tube or sender the float would come loose and move up to the end of the travel. Flip it over to normal orientation, and it would drop but not necessarily drop to the end of its travel.

    Hmm.

    Removing the tube from the float assembly indicated nothing amiss from what I could see. If I manually moved the float it would move up and down all the way without a problem, and I didn't feel any resistance to speak of near the bottom of the float's travel (empty tank). Inspection of the center rod and conducting wires showed nothing that would suggest there was a physical impediment to the float's movement.

    Upon very close inspection of the float, I found the problem.

    The float has two nylon "fingers" that stick out from it that act as guides for the resistance wires that the copper wipers ride on to provide a variable resistance for the gauge. These nylon fingers have a sort of "J" shape or "buttonhook" to them to keep the wires aligned with the float and wipers. One of the resistance wires had slipped out of the "J" and was rubbing or riding on the outside of it. If you look at the picture below, the wire would have been on top of the white nylon piece, not in the slot, or "J". This very slight distortion of the wire actually increased the tension on it, as the wire was no longer in a straight line. To add to this, the tension of the wire was pushing ever so slightly on the "J" shaped finger and when the float got towards the end of the travel (empty tank) the tension was greatest. This would cause the float to hang up or stick when approaching the bottom of the sender.

    Gauge sender float.jpg

    Once the wire was carefully placed back into the "J" there was no longer any tension on it and the float now moved freely in both directions.

    When I reinstalled the float I also cleaned the cover and O rings inside of it, as I found some corrosion in the cover grooves. I also lubricated the O rings with the proper Mercedes-Benz rubber lubricant.

    Dan

    1993 400E Fuel Gauge Sender - 1.jpg1993 400E Fuel Gauge Sender - 2.jpg1993 400E Fuel Gauge Sender - 3.jpg1993 400E Fuel Gauge Sender - 5.jpg1993 400E Fuel Gauge Sender - 4.jpg1993 400E Fuel Gauge Sender - 6.jpg
    Last edited by LWB250; 05-27-2018 at 07:41 AM. Reason: edited wording to clarify

  2. The Following 8 Users Say Thank You to LWB250 For This Useful Post:

    a777fan (05-26-2018), emerydc8 (05-28-2018), gsxr (05-26-2018), Kip (05-27-2018), Klink (05-27-2018), nocfn (05-27-2018), sheward (05-27-2018), skikrazey (05-27-2018)

  3. #2
    .036 Hoonigan™
    E500E Boffin
    gsxr's Avatar
    Join Date
    Dec 2008
    Location
    Boise, ID, USA
    Posts
    21,325

    Re: Fuel Gauge Reads Inaccurately Near Empty

    Dan, thanks for the writeup & photos!

    Can you share the part number for the MB Spezial-Gleitmettal? Do I even want to know how much it costs?

    Dave M.
    1997 E420 (Bugeyes)
    1994 E420 (Blondie)
    1994 E500 (Q-ship)
    1992 500E (Mach 5)
    1987 300D (Sportline Stage 2)
    Click here for my website
    Click here for my YouTube channel

  4. #3
    Senior Member LWB250's Avatar
    Join Date
    Feb 2018
    Location
    Tampa, FL
    Posts
    230

    Re: Fuel Gauge Reads Inaccurately Near Empty

    Quote Originally Posted by gsxr View Post
    Dan, thanks for the writeup & photos!

    Can you share the part number for the MB Spezial-Gleitmettal? Do I even want to know how much it costs?

    I'll dig the part number up and post it later this morning. It's actually the stuff that is used to lubricate the rubber seals for the convertible and hard tops, but I have used it on O rings and such as well. I believe that bottle is between $30-$40, but once I get the number you can look up the current price. Just like all the other special lubricants, it's pricey, but it sure does a good job.

    Dan

  5. The Following 2 Users Say Thank You to LWB250 For This Useful Post:

    gsxr (05-27-2018), Klink (05-27-2018)

  6. #4
    Senior Member LWB250's Avatar
    Join Date
    Feb 2018
    Location
    Tampa, FL
    Posts
    230

    Re: Fuel Gauge Reads Inaccurately Near Empty

    Part number is 000 989 36 60 - Spezial Gleitmittel, Fluid. Looks like it's around $45.00 for a bottle these days. Yikes!

    Good stuff, however, and it's not like you're slathering it all over the place. I lube my R129's top and door seals annually and I've had it for about three years, I think.

    Dan
    Last edited by LWB250; 05-27-2018 at 07:42 AM.

  7. The Following 4 Users Say Thank You to LWB250 For This Useful Post:

    a777fan (05-27-2018), emerydc8 (05-28-2018), gsxr (05-28-2018), Klink (05-27-2018)

  8. #5
    E500E Guru captruff's Avatar
    Join Date
    Jul 2009
    Location
    Orange County
    Posts
    1,730

    Re: Fuel Gauge Reads Inaccurately Near Empty

    Quote Originally Posted by LWB250 View Post
    Part number is 000 989 36 60 - Spezial Gleitmittel, Fluid. Looks like it's around $45.00 for a bottle these days. Yikes!

    Good stuff, however, and it's not like you're slathering it all over the place. I lube my R129's top and door seals annually and I've had it for about three years, I think.

    Dan
    +1 excellent product although I seem to go through at least one bottle per year.

    Jeff
    "Nice Things Cost Money" - Oskar Schindler

  9. The Following 3 Users Say Thank You to captruff For This Useful Post:

    gerryvz (05-27-2018), gsxr (05-28-2018), Klink (05-27-2018)

  10. #6
    Senior Member LWB250's Avatar
    Join Date
    Feb 2018
    Location
    Tampa, FL
    Posts
    230

    Re: Fuel Gauge Reads Inaccurately Near Empty

    Quote Originally Posted by captruff View Post
    +1 excellent product although I seem to go through at least one bottle per year.

    Jeff
    Looks like I've used about half of my bottle and as I said I think it's about three years old. I glove up when I use it so it doesn't get absorbed into my skin, if it can be. For what it does (lubricates and rejuvenates rubber seals) it's great stuff. Keeping the seals lubed on the convertibles is critical to preventing leaks and wind noise.

    Dan

  11. The Following 3 Users Say Thank You to LWB250 For This Useful Post:

    a777fan (05-27-2018), gsxr (05-28-2018), nocfn (05-27-2018)

  12. #7
    .036 Hoonigan™
    E500E Boffin
    gsxr's Avatar
    Join Date
    Dec 2008
    Location
    Boise, ID, USA
    Posts
    21,325

    Re: Fuel Gauge Reads Inaccurately Near Empty

    Egads, $53 MSRP is for ONE fluid ounce? Anyone know of a less-costly equivalent? I'll still pick up a bottle, but it would be nice to source alternatives!


  13. #8
    Senior Member LWB250's Avatar
    Join Date
    Feb 2018
    Location
    Tampa, FL
    Posts
    230

    Re: Fuel Gauge Reads Inaccurately Near Empty

    Quote Originally Posted by gsxr View Post
    Egads, $53 MSRP is for ONE fluid ounce? Anyone know of a less-costly equivalent? I'll still pick up a bottle, but it would be nice to source alternatives!

    Yes, but it's made with the tears of (German) unicorns..... As in crunchy frogs:

    "We use only the finest baby frogs, dew picked and flown from Iraq, cleansed in finest quality spring water, lightly killed, and then sealed in a succulent Swiss quintuple smooth treble cream milk chocolate envelope and lovingly frosted with glucose."

    Mr_Milton.jpg

    -Monty Python, "Trade Description Act"

    Dan

  14. The Following User Says Thank You to LWB250 For This Useful Post:

    gsxr (05-28-2018)

  15. #9
    Site Honcho
    Klugscheisser
    Ich bekenne mich
    nicht schuldig.
    gerryvz's Avatar
    Join Date
    Nov 2008
    Location
    Annapolis, MD
    Posts
    17,674

    Re: Fuel Gauge Reads Inaccurately Near Empty

    Quote Originally Posted by LWB250 View Post
    Yes, but it's made with the tears of (German) unicorns..... As in crunchy frogs:

    "We use only the finest baby frogs, dew picked and flown from Iraq, cleansed in finest quality spring water, lightly killed, and then sealed in a succulent Swiss quintuple smooth treble cream milk chocolate envelope and lovingly frosted with glucose."



    -Monty Python, "Trade Description Act"

    Dan
    Sounds like the orange anaerobic sealant for M119 cam magnets, which is made from koala claws and a special species of satsuma.

  16. The Following User Says Thank You to gerryvz For This Useful Post:

    lowman (05-28-2018)

  17. #10
    E500E Guru
    Join Date
    Feb 2011
    Location
    DFW Texas
    Posts
    2,662

    Re: Fuel Gauge Reads Inaccurately Near Empty

    You can buy or in lube from most come racial suplier and still fill your tank w the remaining $$

  18. #11
    .036 Hoonigan™
    E500E Boffin
    gsxr's Avatar
    Join Date
    Dec 2008
    Location
    Boise, ID, USA
    Posts
    21,325

    Re: Fuel Gauge Reads Inaccurately Near Empty

    Quote Originally Posted by samiam44 View Post
    You can buy or in lube from most come racial suplier and still fill your tank w the remaining $$
    Link? Brand name / part number?


Similar Threads

  1. Fuel gauge fluctuation
    By gerryvz in forum Troubleshooting and Diagnostics
    Replies: 34
    Last Post: 04-25-2017, 01:42 AM
  2. HOW-TO: Recalibrate 300E Fuel Gauge to Work With 500E Fuel Sender
    By Jlaa in forum "HOW-TO" Tutorial Articles
    Replies: 0
    Last Post: 04-25-2017, 12:43 AM
  3. Fuel gauge needle is erratic
    By ffinn in forum Electrical, CAN and Wiring
    Replies: 14
    Last Post: 02-18-2017, 03:01 AM
  4. WTB: Fuel/Oil/Temp Gauge Pod
    By remotemark in forum Wanted to Buy
    Replies: 0
    Last Post: 07-18-2012, 03:07 PM
  5. Fuel Gauge Sender
    By askd9280 in forum Electrical, CAN and Wiring
    Replies: 2
    Last Post: 01-15-2012, 03:06 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •