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  #1  
Old 09-19-2009, 05:44 PM
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1975 300D Fuel Gage

Hi, I have just purchased a 300D, 6600 miles on it, and I'm having trouble getting the fuel gage to read. I filled the tank, but it shows it's empty. The oil pressure, temperature gage all work, it's just the fuel gage not reading. I checked the sensor in the trunk above the tank and it is getting voltage as well. Anyone know what could be wrong? Thanks.

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Old 09-19-2009, 06:02 PM
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Even if the sensor is getting voltage, they usually get gunked up and have to be cleaned or replaced. Unscrew it (have a tupperware pan to catch the fuel), take it out, take off the cylinder cover and clean the unit with keroscene. If one of the three wires is broken, get a new sender unit.
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Old 09-19-2009, 06:07 PM
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If the sender unit was stuck at the bottom, would the low fuel light be on?
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Old 09-19-2009, 06:32 PM
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Quote:
Originally Posted by Dynotoaqrimp View Post
If the sender unit was stuck at the bottom, would the low fuel light be on?
It would but then the warning light would have to be on that's if it was stuck right at the bottom enough to touch the contacts.
Do this: there are three wires that go to the fuel floater remove then and touch them all together and have someone check the instrument cluster for the low fuel warning light (orange on my dad's W115) and the fuel gauge should swing right to full which proves there is no probem with the conections or the little motor that swings the needle, remember in the trunk there are three wires touch them all together so they all have contact and check for operation of the warning light and see if the needle swings over.
After you have tried this and if the test shows that there are no problems their now you would have to remove the fuel floater (sensor) you could open it up if you want to try and fix it I do myself because my dad would have to travel to Colombo in order to get parts which is a little dicey due to availability around here so if you want to go through fixing it post back, it should take around say 10 minutes tops to get it fixed its not that hard and cost's very little for a yard of nichrome wire it cost's me 10 RS for the nichrome to get it fixed having said that you must have a soldering iron and a little soldering wire.

Hope this helps you good luck
Jeremy Brett
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Old 09-19-2009, 10:06 PM
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How do you gain access to the sendor in the tank on a W114-W115?
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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

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1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

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Old 09-20-2009, 02:36 AM
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Originally Posted by 79Mercy View Post
How do you gain access to the sendor in the tank on a W114-W115?
when you open up the trunk and lift up the mats there should be a cover on the trunk floor, after you get that off you can see the top of the fuel floater and there are I think six nuts around it so after those nuts are removed the you can pull the floater up

Jeremy Brett
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Old 09-20-2009, 11:16 AM
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The low fuel light only comes on when the float is at the very, very bottom.

When we took apart the one on my friends 1976 we couldn't believe how gunky it was They clean up nicely though. Very German design.

-Jason
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  #8  
Old 09-20-2009, 01:34 PM
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yes thats true and the thin nichrome wires break so easy
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  #9  
Old 09-20-2009, 01:37 PM
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Okay I got my sender unit out, and tested the wiring and the needle jumped to full. However, now I cannot figure out how to open the unit to clean it. Am I supposed to just drop it in kerosene and hope it cleans itself? Edit: I got it to work! I got to the sending unit, cleaned it with kerosene and put it back in, and it registered a full tank! Thanks all!

Last edited by Dynotoaqrimp; 09-20-2009 at 02:04 PM.
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  #10  
Old 09-20-2009, 02:30 PM
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My 300D had a recessed nut on the bottom, unscrew that and the bottom plates will come off and the tube surrounding the guts of the unit will slide off as well...be forewarned! the wires are really delicate and be certain to go at the cleanup gently, a little patience will go a long way. I used Q-Tips and solvent to remove the sludge. You'll see that the float runs up and down two wites as well as a center guiderod. Be Careful of the area where the wires pass near to the float, there are little contact "wipers" in the float that complete the electrical connection to the sending unit, I didn't realize their importance until I opened up the unit a second time to find out why the gauge was jumping all over the place --- my bad, the wipers weren't connecting with the wire...

Easy cheap fix, if your patient....I also had to re-solder a wire because I'm still learning patience...

Reminder! When you disassemble this, don't do it on the dining room table...amazing the "stuff" that came out of my unit!

Fuel Sending Unit Threads
Fuel Gauge and Sending Unit threads

good luck

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