Fuel sender repair - Page 2 - Mercedes-Benz Forum
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post #11 of 41 (permalink) Old 07-02-2013, 03:18 AM
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post #12 of 41 (permalink) Old 01-05-2014, 05:35 PM
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Happy new year drivers...
Found this thread while shopping for a 1980 450sl fuel sender.
The fuel gauge on my 1980 450 was erratic at best then stopped working altogether then I finally decided to investigate. Looks like my sender was replaced by the previous owner as the bottom of it was compressed like an accordian and I think this replacement was adapted to fit as it seems longer than the origional. I am looking for a 2nd hand replacement if anyone could offer any leads or has one for sale.. Thank you in advance.
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post #13 of 41 (permalink) Old 01-05-2014, 05:49 PM
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Welcome to the board.

There are several contributors out there with cars in various stages of being parted out, they'll be along...
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post #14 of 41 (permalink) Old 01-06-2014, 05:11 AM
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I have one for a '79..Came from a parts supplier when I was fighting fuel system problems. I had already bought a new sender..and this one came in a replacement tank I bought. It was guaranteed and looks fine..Jerry ...870-847-5771..anytime..
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post #15 of 41 (permalink) Old 02-08-2016, 04:01 AM
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I took mine out this weekend and found that the thin wire was broken. I replaced the wire with a copper wire, but now when you insert the unit in the tank it reads full all the time. I am guessing the thin wire was some type of material that it did not had continuity when inmersed in fluid. Any one has an idea of what will be a proper repair for a broken thin wire?
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post #16 of 41 (permalink) Old 02-08-2016, 08:23 AM
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After some reasearch the resistor wires needs to be Nichrome. Does anyone know the proper gauge of the O.E.M. resistor wire, I can not find the broken piece. 36AWG, 38 AWG, 40AWG?
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post #17 of 41 (permalink) Old 02-08-2016, 08:33 AM
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That wire is made of an alloy that has a certain amount of resistance. The float grounds that wire, so it's essentially working to make the wire "longer" and therefore increasing the resistance. It's the same kind of wire used in, say, a toaster because it gets hot when you put voltage into it.

On my 560SL the resistance measures from 3 Ohms when full and 69 Ohms when it reaches the reserve fuel amount. (Which is helpful to know when trying to diagnose a fault in the gauge cluster.) The copper wire you replaced it with has almost zero resistance, which is why the gauge reads full.

You can find such wire on eBay, and the data you need is the Ohms per foot, and the exact length of the wire needed. Resistance Heating Wire | eBay Note that the "40 gauge Kanthal D resistance wire–Resistance- 84 ohm/ft 275 ohms/m" sounds about right, but you'll have to do the algebra to get it exactly right. If you have an industrial wire shop where you live, they might be more helpful in finding the right type of wire.

I'm not an electrical engineer, but my best guess is that you'll find it easier just to buy a new sender, but if you successfully pursue just replacing the wire, it would help folks if you let us know which kind of wire worked correctly.

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post #18 of 41 (permalink) Old 02-08-2016, 09:01 AM
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Got it, when the float is up, the distance from contact points is short, therefore the 3 Ohms, When the float is on the bottom I need to measure the amount of cable between the contact points
and determine the proper resistor cable gauge and Ohm/ft that matches the 69 Ohms reading when the float is at the bottom. I don't feel like spending $200+ dollars for a new sending unit
If I can solder a $5.00 piece of wire to solve the problem, I enjoy the work and the challenge!!

Last edited by ivanuf; 02-08-2016 at 09:03 AM.
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post #19 of 41 (permalink) Old 02-08-2016, 09:10 AM
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My sentiments exactly.

Now that I think further about it, 3 Ohms at full is probably just a measurement error, because the way the gauge works in relation to vehicle ground ideally it would be 0 Ohms when full. But any fuel gauge is going to be a rough approximation anyways, otherwise they'd put little numbers on the gauge so we could know the exact amount.

There's got to be interesting ways to use the leftover 49 feet of wire.

Tom
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post #20 of 41 (permalink) Old 02-08-2016, 09:26 AM
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Just an fyi...while many parts are interchangeable with the W126 models (560SEL/C etc) the fuel sender is not one of them. The 126 unit is about two inches longer...IIRC.
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