Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 10-28-2004, 10:29 AM
Registered User
 
Join Date: Mar 2004
Location: Kansas City, MO, USA
Posts: 1,213
Fuel level sending unit question

My low fuel level light only comes on when the tank goes completely empty. Furthermore, once I get down to about 8 gallons in the tank, the fuel level gauge goes down to R and stays there forever. From what I found out from searches and from my own suspicion, this means my fuel level sending unit is messed up right? Just wanted to get the opinions of techs or people who have gone through this before I purchase a new sending unit and start the replacement task. Thanks. Oh, car is the '84 300SD.

__________________
1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver
Reply With Quote
  #2  
Old 10-28-2004, 11:48 AM
Registered User
 
Join Date: Mar 2004
Location: Kansas City, MO, USA
Posts: 1,213
Also I forgot to mention that my temperature gauge isn't working properly. I already changed the sending unit but it still flickers sometimes. Now that I think of it, the temperature and fuel level gauges are on the same part of the instrument panel. Maybe that is really messed up.
__________________
1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver
Reply With Quote
  #3  
Old 10-28-2004, 12:42 PM
dmorrison's Avatar
Registered User
 
Join Date: Dec 2002
Location: Colleyville, Texas
Posts: 2,694
Some considerations

This post is based on my W123 work, I dont' have a 126 manual anymore since the 300SDL is gone. So minor variations may exist. Someone with a 126 will correct me if I'm wrong, I'm sure.

I played with the fuel sending unit on my daughters 240D.
The lack of a correct indication could be due to algae/crud on the sending unit wires. Remove the unit and open it up. Clean it with carb cleaner. It will take 2-3 cans of carb cleaner.

Removing the sending unit.

W126 removal of 1st aid kit box

Then open the sending unit by unscrewing the nut at the bottom. Slide the tube off the assembly. Be careful not to damage the 2 wires. Clean the unit completely with carb cleaner. Check the resistance at the plug with an ohm meter while sliding the float up and down, this will make sure your unit is making contact. Also check the reserve light contact. Reassemble and install with a new Oring.

Here is the SM for the W123

http://skinnerbox.steaky.org/Service/W123/Index/617T/47FuelSystem.htm

Also the reserve light goes thru the seatbelt warning relay. My daughters light did not work. I replaced the seatbelt relay and it now works. Test the light first. Test the reserve contact in the sending unit. If they both check OK then it could be the seatbelt relay.

These proceedures shold be covered in the Service Manual.

Dave
__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car
Reply With Quote
  #4  
Old 10-28-2004, 03:04 PM
oldnavy's Avatar
Registered User
 
Join Date: Apr 2004
Location: SwampEast MO
Posts: 1,695
My 240D didn't have a nut at the bottom of the sender so I could take it apart, I may pull it in a day or two and look at it closer. All I did when I had it out in the spring was spray carb cleaner into the holes and let it drain.
__________________
'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.
Reply With Quote
  #5  
Old 10-28-2004, 07:57 PM
Dan Howard
Guest
 
Posts: n/a
Quote:
Originally Posted by oldnavy
My 240D didn't have a nut at the bottom of the sender so I could take it apart, I may pull it in a day or two and look at it closer. All I did when I had it out in the spring was spray carb cleaner into the holes and let it drain.
My 240 didn't appear to have a nut. It had a small round thing which screwed onto the center rod. I used channel locks to remove it CCW. It was full of junk which kept it from reading accurately. It had three wires inside. Delicate.

Dan
Reply With Quote
  #6  
Old 10-28-2004, 09:37 PM
"Da Benzito"
 
Join Date: Oct 2004
Location: Durham, NC
Posts: 106
I had a similar problem with the gauges on my 300sd. Started of the fuel gauge didn't meaures the fuel in the tank properly. Learned a whole lot from dissassembling and reassembling various clusters. Now, five clusters later, I have a fully functional unit. I have 2 or 3 300sd gauge clusters laying around at the house, but can't remeber which one's have good gauges, and which ones have bad gauges. If it comes down to it you should be able to buy a whole entire cluster for less than 100 dollars. Check ebay, user id usedpartshunter, that is who I got mine from. If you have access to a gasoline speedometer though, you might be able to make it work to an acceptable degree. Of course the diesel units don't have the economy gauge, but other than that, the oil, temp, fuel gauges are virtually the same. You would though have to get a wiring diargram of the cluster and rearrange the pins to match the gasoline's board arrangement. Probably eaisier just to get another one though.
Reply With Quote
  #7  
Old 10-28-2004, 11:39 PM
oldnavy's Avatar
Registered User
 
Join Date: Apr 2004
Location: SwampEast MO
Posts: 1,695
Quote:
Originally Posted by Dan Howard
My 240 didn't appear to have a nut. It had a small round thing which screwed onto the center rod. I used channel locks to remove it CCW. It was full of junk which kept it from reading accurately. It had three wires inside. Delicate.

Dan
Thanks Dan, I'll give that a try tomorrow.
__________________
'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.
Reply With Quote
  #8  
Old 10-29-2004, 02:51 AM
Brandon314159
Guest
 
Posts: n/a
The carb clean works magic..
I ran a bunch through mine and it seems to be ok now
a lot smoother
Why does my 300SD w126 only seem to have a 18 gallon tank?
I looked it up and it is supposed to be more?
Reply With Quote
  #9  
Old 08-18-2007, 02:11 PM
atombaum's Avatar
Registered User
 
Join Date: Oct 2000
Location: western Finger Lakes region of New York state
Posts: 120
related (W123) fuel level sending unit question

Hello,

My low fuel warning light started to come on dimly this week, with more than half a tank of fuel (240D). When I topped off the tank, the light went out for a few miles. Then it came back on. Today, I replaced the voltage regulator to no avail, and checked the fuel level sending unit, but I did not get the fastener off the bottom, so I did not inspect the wires. It seemed like some black crud was coming out the top holes when I held it upside down. Is this probably a sending unit issue? I only replaced it seven years ago when I got the car because it was not working at all at that time. Price of a new unit must be over $100 by now. Don't want to spend it if I don't have to. BTW, this 240D now has 353,576 miles.
__________________
- Jeff

1957 W121 190 (history)
1966 W108 250S
1967 W108 250S (parts)
1982 W123 240D (history)
1989 W124 260E
Reply With Quote
  #10  
Old 08-18-2007, 03:42 PM
oldnavy's Avatar
Registered User
 
Join Date: Apr 2004
Location: SwampEast MO
Posts: 1,695
Quote:
Originally Posted by atombaum View Post
Hello,

My low fuel warning light started to come on dimly this week, with more than half a tank of fuel (240D). When I topped off the tank, the light went out for a few miles. Then it came back on. Today, I replaced the voltage regulator to no avail, and checked the fuel level sending unit, but I did not get the fastener off the bottom, so I did not inspect the wires. It seemed like some black crud was coming out the top holes when I held it upside down. Is this probably a sending unit issue? I only replaced it seven years ago when I got the car because it was not working at all at that time. Price of a new unit must be over $100 by now. Don't want to spend it if I don't have to. BTW, this 240D now has 353,576 miles.
Get some carb cleaner and use the little tube to stick in the holes and clean that crap out of the inside, it may work by then. Also you will most likely need to clean the fuel tank and lines of this black gunk at some point.
__________________
'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.
Reply With Quote
  #11  
Old 08-18-2007, 08:41 PM
Stevo's Avatar
Registered User
 
Join Date: Apr 2002
Location: NW WA
Posts: 6,296
Quote:
Originally Posted by oldnavy View Post
My 240D didn't have a nut at the bottom of the sender so I could take it apart, I may pull it in a day or two and look at it closer. All I did when I had it out in the spring was spray carb cleaner into the holes and let it drain.
That little nut on the bottom of the sender has something like a tight fitting little "round" of plastic tubing surrounding it. I just preyed if off, undid the nut, fixed the sender and used thread lock on the nut when reassembling.
__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"
Reply With Quote
  #12  
Old 08-18-2007, 09:08 PM
oldnavy's Avatar
Registered User
 
Join Date: Apr 2004
Location: SwampEast MO
Posts: 1,695
Quote:
Originally Posted by Stevo View Post
That little nut on the bottom of the sender has something like a tight fitting little "round" of plastic tubing surrounding it. I just preyed if off, undid the nut, fixed the sender and used thread lock on the nut when reassembling.
Come to think of it I think I did finally get the nut off, because I did eventually get it apart, just been so long I forgot. My memory is not what it use to be to say the least.
__________________
'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.
Reply With Quote
  #13  
Old 08-18-2007, 09:12 PM
Stevo's Avatar
Registered User
 
Join Date: Apr 2002
Location: NW WA
Posts: 6,296
Quote:
Originally Posted by oldnavy View Post
My memory is not what it use to be to say the least.
LOL, Yah me too...what were we talking about?
__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"
Reply With Quote
  #14  
Old 08-19-2007, 12:28 AM
atombaum's Avatar
Registered User
 
Join Date: Oct 2000
Location: western Finger Lakes region of New York state
Posts: 120
Quote:
Originally Posted by Stevo View Post
That little nut on the bottom of the sender has something like a tight fitting little "round" of plastic tubing surrounding it. I just preyed if off, undid the nut, fixed the sender and used thread lock on the nut when reassembling.
I figured if I started prying that little plastic tubing off, that would be the end of the sending unit but I could bring the unit into the shop tomorrow and attempt it.
__________________
- Jeff

1957 W121 190 (history)
1966 W108 250S
1967 W108 250S (parts)
1982 W123 240D (history)
1989 W124 260E
Reply With Quote
  #15  
Old 08-19-2007, 12:54 AM
Stevo's Avatar
Registered User
 
Join Date: Apr 2002
Location: NW WA
Posts: 6,296
Quote:
Originally Posted by atombaum View Post
I figured if I started prying that little plastic tubing off, that would be the end of the sending unit but I could bring the unit into the shop tomorrow and attempt it.
I got into one where the little wire was broken at the bottom. A friend held it and I soldered it back together. I tucked it away for a spare and didn't try it, but I think its fixed

__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 12:12 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page