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  #1  
Old 05-28-2002, 10:47 AM
jeff karg
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Gas gage

New vehicle for us... '82 240D with a gas gage that reads 1/3 when empty. Will stay on full for first 180 miles. Seems consistant. Is this a matter of bending the tank float or an electric adjustment? How do I access the float?

Running out gave me a reason to replace the leaky primer pump with the new improved non screw-in type. and I'm thankful for that $20. upgrade. But short of using the trip odometer and a pessimistic guess on MPG this could lead to some agravating moments.

Thanks for the assist.

Jeff

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  #2  
Old 05-28-2002, 12:09 PM
Senior Member
 
Join Date: Jul 2001
Location: San Antone
Posts: 408
Probably a dirty or broken fuel sendiing unit is causing your fuel gauge to read wrong - the FSU malfunctioning is a common problem. The sending uint can be removed through the med kit and the fuel tank is in the trunk behind a metal panel. Look up an old reply by me in the Diesel Forum about working on the FSU - lots of good info!

Good Luck!
Tom
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1977 300D: 300,000+ miles

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  #3  
Old 05-28-2002, 03:11 PM
Former Dieselholic
 
Join Date: Feb 2002
Location: West Michigan
Posts: 380
Unhappy Same thing...

I also have the same problem. I recently purchased an 83 240D and the fuel light came on. The PO said that there was 2 or 3 gallons as he could get 50 or 60 miles after that.
I filled up with 13.xx gallons (17 gal capacity) and when it drained (415 miles later) the light came on.
Now, 2-fillups later, I was at 402 miles and the light never came on. I was driving to work when I completely ran out and had to coast into the nearest station. Luckily it was going downhill and the station was right at the bottom of the hill! I filled up with 17.02 gallons.

I will attempt to check the FSU as I do not want to keep draining my tank completely and I *REALLY* don't want to get stranded...
__________________
Current: '91 300TE 4MATIC 317k and climbing...
Former:
'81 300TD Wagon 168K "Tank"
'83 240D 216K 4spd manual "Da Bear" (aka best car ever)

"Never sweat the petty things...
and never pet the sweaty things."
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  #4  
Old 05-29-2002, 01:29 PM
PeterG
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If you have some spare time You might find removing and cleaning it up, it will be as good as new. Here is a post I sent quite a while ago.

PeterG

79 300 SD 75K miles

As I stated before the sending unit is somewhat delicate, so treat it with care. The first thing I would suggest is disconnecting the battery. This is added insurance to make sure we donít short something out. On my 300 SD, the sending unit was located under the hat shelf (as it is called in my book) under the first aid cavity compartment. I had some trouble getting that compartment out. My rear deck has seen some better days, and it seems the compartment was somewhat brittle. I think there were four screws that held it in. Under that compartment is the sending unit (another reason why MB are so great). Maybe before you go any farther get the pan and rags mentioned below,and a permanent marker, and some tape wide masking or duct tape would be ideal.
The sending unit has a connector on the top that pulls off, straight up. Now place a mark on the sending unit, and the tank. You will use these as your line up marks when reinstalling and tightening the sending unit, unless you have a torque spec and torque wrench and the correct socket in the next paragraph. The top of the sending unit is a huge nut (1.856" or 47 and some MM). Unfortunately I did not have a socket or wrench to fit it, so I used a large pair of channel locks. It is a right hand thread(righty tighty,Lefty loosy). I backed off the nut (which is the sending unit) and withdrew the unit. Have a pan or something because the sending unit will be filled with fuel, depending on how much fuel is in the tank. Like mine the holes were partially blocked, and I had to let it stand over the tank for a while to drain. (I had not planned for this, as I had nothing close by,or rags). The unit is about 3" in diameter and 8" to 12" long. At this point take that tape, and put an FME cover over the hole. (Foreign Material Exclusion) Nuclear plant terminology and a good practice for anything left open.
On the bottom of the unit I believe there was a nut, that holds the assembly together. I loosened the nut and gently tapped on the side to release the can around the sending unit (a coating from the fuel forms locking this assembly together). Once inside look at how it operates. The fuel fills up the can slowly through the holes in the side and moves the float up and down. Now observe the bottom plate. It has almost a circular mouse maze the fuel follows into the sending unit (I think this is used for dampening when the fuel gets down very low). Mine was very dirty. I carefully separated the sections (Make note how they come apart so you donít mix them up) and cleaned them in mineral spirits. Going back to the sending unit, the float (if I remember correctly) rides up and down on a resistive rail. I cleaned this (the rail) with Q-tips and mineral spirits. At the bottom of the travel (float all the way down) there are two contacts. These activate your reserve light (Contacts on float touch contacts on housing assembly). I used Q-tips and mineral spirits, but I think I also took an eraser from a pencil and rubbed them a little. I had the liberty of checking this out with a ohm meter to check continuity.
I then took the unit back to the car, Plugged it in,(make sure it is not positioned in such a way that the internals can short out on something metal) hooked up the battery, turned the key on and exercised it and observed the gas gauge. Note:I donít remember if I had to take the unit and ground it by touching it to the tank(it will respond instantly because it is now not dampened. I made sure if I moved it slowly the gauge would follow with no dead spots (Gauge bouncing or going in the opposite direction of the float movement). I then took the float all the way to the bottom, or if you have the sending unit vertical, let gravity take place. The light should come on. If everything works, just turn your key off, disconnect the battery, and assemble the unit the way you took it apart. When installing watch that the o-ring is centered in the bottom of the sending unit. You don't want to pinch it, or cut it. I would tighten to the same mark you place on in the beginning. Connect connector reinstall first aid compartment, and enjoy now knowing how many miles to the gallon these soot blowers get. If you have any questions feel free send me a thread. I will answer any questions you have before you attempting it.
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  #5  
Old 05-29-2002, 09:06 PM
jeff karg
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Thanks for the Instructions. Works like a champ. Took about an hour to remove, clean all the crap off and get in back in. Well worth it. Never owned an MB with a working warning light. Can see why. Those contacts sitting at the bottom of the can were sitting in 2 inches of goop. Think I'll work on the wagon's tomorrow if I can find it.

Thanks again.

Jeff
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  #6  
Old 05-30-2002, 09:16 AM
Former Dieselholic
 
Join Date: Feb 2002
Location: West Michigan
Posts: 380
in the wagon...

My '81 300TDT has the 3rd seat, but I am assuming that even without it has to be in the same place:
Under the floor in the middle of the cargo area. Lift the carpet and floor if any (I had to remove the entire 3rd seat...not bad at all) you will see the large hex head with connectors to it.
There she be. I will try the same in my 83 240-D this weekend.
__________________
Current: '91 300TE 4MATIC 317k and climbing...
Former:
'81 300TD Wagon 168K "Tank"
'83 240D 216K 4spd manual "Da Bear" (aka best car ever)

"Never sweat the petty things...
and never pet the sweaty things."
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  #7  
Old 05-30-2002, 02:08 PM
PeterG
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Yea, it is sure nice to know I can depend on the gas gauge. When the light comes on I usually fill it up. If I can only find time to fix the odometer. The last time it worked (for a while) I calculated about 20 to 21 MPG. I have heard discussions of 24 to 28. I wonder if this is for a 79 300SD ?


PeterG

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