fuel gauge

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Pete49
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Model you own: w123
Location: Pt Augusta Sth Australia

fuel gauge

Post by Pete49 » Sat 04 Nov, 2017 2:30 pm

Hi guys. My fuel gauge stopped working today and I cant find the sender to check if its the problem. Checked fuses and they are ok. Just dont want to pull the cluster if the problem is in the sender.
Pete
1978 W123 300D Maple Yellow
1981 W123 300TD Classic White (now sold)
1983 W123 280TE Champagne

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Tony From West Oz
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Re: fuel gauge

Post by Tony From West Oz » Sat 04 Nov, 2017 11:29 pm

Pete,
The fuel sender on a W123 sedan is under the first aid kit. Have a large pair of multigrips to undo it and a container to catch any spilt fuel when you remove the sender unit.
Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

'83 W123 300D 325000km (Wife's car Josephine - sold).
'84 W123 300D replaced good OM617 912 with OM617 952 and enjoyed having good acceleration for the first time since first driving a 300D in 2002 - became engine and trans donor for 300CD Turbodiesel conversion. Now parted out.
'86 W124 300D sold (Wife's old car - sold )
'85 W123 300CD, 275 000km (Fatmobile) rebuilt turbodiesel from previous Fatmobile transplanted into 280CE (occasional tourer)
'99 W202 C250 Turbodiesel (my darling Wife's car - Sold)
'98 W202 C250 Turbodiesel (my car - Sold)
'06 Ssanyong Musso Crew Cab 2WD Ute (OM662 diesel and Auto Transmission)

Pete49
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Re: fuel gauge

Post by Pete49 » Sun 05 Nov, 2017 1:35 pm

thanks Tony I'll remember that one but my bad Its the S123 280TE 7 seater.
1978 W123 300D Maple Yellow
1981 W123 300TD Classic White (now sold)
1983 W123 280TE Champagne

mathuisella
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Re: fuel gauge

Post by mathuisella » Sun 05 Nov, 2017 7:54 pm

I have a friend 2 suburbs away with a 7 seater that i just fixed his fuel sender.

it's in the rear under the carpet, if i remember right you need a 36mm socket and a breaker bar :)

as you take it out, let the fuel drain through the tiny holes as you lift up, it might take 10 minutes to drain, but you'll be glad you did, saving yourself 2 years of cleaning the fuel smell out of your interior.

undo the bottom little plastic screw and you'll probably find yourself with a fuel sender that's just a bit gummed up from years of use.

clean it all with methylated spirit and be extremely careful not to break the thin/tiny wires.

please post pictures if you need any help further with it :)

I'd be happy to do it for you if you're in brisbane :)

Pete49
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Re: fuel gauge

Post by Pete49 » Mon 06 Nov, 2017 1:41 pm

Thanks for the info Math. I'll give it a look later. Won't be in Brisbane until sometime next year to visit the boy :)
Pete
1978 W123 300D Maple Yellow
1981 W123 300TD Classic White (now sold)
1983 W123 280TE Champagne

mathuisella
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Re: fuel gauge

Post by mathuisella » Thu 16 Nov, 2017 5:29 am

https://mercedessource.com/store/123-30 ... -unit-used

from the above link

Access to this sender is under the rear floor panel / mat. If your fuel guage is not reading properly or sticking at 1/4 of a tank this is most likely the cause.


my own words > I've cleaned 4 of these now, and they all work again.



You will need a 46mm Socket. a shifting spanner or multigrips just don't cut it with this. Also, i suggest when you get the socket, you get one with a hole towards the top so you can put a 5 or 6mm rod through the side of it to turn it in tight spaces, trust me you will when you have to pull the intank filter/strainer

and saying that, when you get this socket, make sure it's flat on the bottom of it where the socket inside makes contact to the sending unit. make sure it's not tapered, you can use an angle grinder to take off the taper. I'll be doing this myself tomorrow morning after 9am ( noise restrictions and being nice to the neighbours )

( i'm currently taking an intank filter from my doner car to my good car, previous owner cut the strainer off which has made the filters down the line clog up so much. )


anyways, back to cleaning this sender.
sending.JPG
under the carpet, pretty much in the centre of the back section of the car, i don't believe you need to take the last row of reverse facing seats out to get to it, just lift up the carpet completely in the "boot" area of the wagon. It's right in the middle, if you're having a bit of trouble, look under the car where the fuel tank is, that'll give you an idea.

disconnect the sending unit plug/wires and set aside, note it's orientation, it only goes on/off one way, so never force it, it goes on in a strange manner to those 1st timers


okay, so use the 46mm socket get a 6 sided socket, not a 12 sided, you cannot afford to accidently strip the soft aluminum edges with a hardened steel 12 sided socket that slips....

carefully lit up the sending unit, letting all the diesel flow out of it as you lift, this will take a few minutes. Have a milo tin and a towel in the immediate area to soak up an spills and put the sending unit in the milo can and let the milo tin catch any remaining diesel as you open it up.


Ok, how to open it up.

at the base of the sending unit, you will see a small plastic like smooth circular "nut" use a pair of pliers, pinch this carefully and undo it, this will release the plastic and metal plates.

once they are off, note the top of the silver tube, as you pull the tube off/away from the "top" of the sending unit itself. ( where you attach the 46mm socket is the "top" ) there will be a tiny notch. cutout. this is the way to reassemble.


once it's apart, you'll be met with the following
15135805_10209413684911861_2469305130141188903_n (1).jpg
Usually the inner metal rod is all gummed up, also inside the black float as well it will be very gummy. I've seen it very bad... like below... Clean all the contacts, especially the ones at the base where the float will fall to when on reserve, the contacts here will activate the reserve fuel light on the dash.
YUCK!!!
23335770_10212523046563959_9066778_o (1).jpg
i suggest being very careful not the break the super thin wire. It's very difficult to find, takes forever to ship to you and is a bitch to work with and get nice and taught and soldered up, trust me i know.

Use kerosene as your cleaning agent, and a small paint brush to clean it up, and a soft tooth brush for the more stubburn parts.


Paper towel to carefully wipe it all down once done and reassemble.

Note: you can test the level by attaching the plug before reassembly and move the float by hand to see if the needle moves in sync with the float. in most cases it will be close, but not perfect other than when it's on reserve/empty or full tank. everything else in between is arbitrary and after time you'll get to know your car.

if you've got any questions i'm happy to answer, I have a sending unit disassembled at the moment i can take pictures of if you or anyone needs clarification :)
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Pete49
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Re: fuel gauge

Post by Pete49 » Mon 20 Nov, 2017 1:35 pm

Thanks for the help I've now found it and had to borrow a socket from a mate so will get to it when its a bit cooler in the next day or two and report back.
Pete
1978 W123 300D Maple Yellow
1981 W123 300TD Classic White (now sold)
1983 W123 280TE Champagne

Pete49
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Joined: Thu 09 Oct, 2014 4:42 pm
Model you own: w123
Location: Pt Augusta Sth Australia

Re: fuel gauge

Post by Pete49 » Fri 24 Nov, 2017 2:07 pm

Well I got the fuel gauge out of the tank this morning and saw immediately why it wasn't working.....The wires were broken. It looks like the bottom of the tube the float is in lost the nut holding the bottom plate on undid itself and the plate dropped off and I cant see it (the plate) or the nut and surmise that's what broke the wires. I can make a plate and have a nut the right size. I've soldered up the copper wire as it was only off at the bottom but the other wire has me stumped as its double the length of the unit and was totally disconnected and I can't tell where to attach it.
Any pics or drawing that can help? or do I need to buy a new one? :angryfire:
Pete
1978 W123 300D Maple Yellow
1981 W123 300TD Classic White (now sold)
1983 W123 280TE Champagne

mathuisella
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Re: fuel gauge

Post by mathuisella » Fri 24 Nov, 2017 3:09 pm

okay, so the single length wire that just connects top to bottom is for the circuit that turns on and off the fuel reserve light when the "float" goes all the way to the bottom and touches the metal contacts ( test this out with a helper looking at the dash fuel reserve light/gauge )

the other is a bit more complicated, it's the one that's twice as long as the unit itself.

i'll take a few pictures, that'll help

see how the thin wire wraps around ? it's best to do this with 2 people, one holds the float and stuff while the other stratches the wire around and solders or however you need.
23998411_10212670451408988_1364057209_o.jpg
24093751_10212670451248984_387566650_o.jpg
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23961018_10212670451568992_195838076_o.jpg
24085465_10212670451168982_667426405_o.jpg

note the metal contact points under the float and where they coll hit when the fuel level gets low... make sure those are clean...

Hope this helps :)
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Pete49
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Re: fuel gauge

Post by Pete49 » Sat 25 Nov, 2017 1:12 pm

Mathuisella it helped BUT the wire was too short ( broke part way up) and I don't have anything that thin or type so now I will need to buy a replacement. Not happy Jan :angry4: Any ideas? has anyone got one spare they are willing to part with or do I go to MB Spares and hope they have one?
Pete
1978 W123 300D Maple Yellow
1981 W123 300TD Classic White (now sold)
1983 W123 280TE Champagne

mathuisella
Adenauer
Posts: 383
Joined: Sun 08 Jun, 2014 7:03 am
Model you own: w123
Location: Brisbane, North side.

Re: fuel gauge

Post by mathuisella » Sat 25 Nov, 2017 11:39 pm

Pete49 wrote:
Sat 25 Nov, 2017 1:12 pm
Mathuisella it helped BUT the wire was too short ( broke part way up) and I don't have anything that thin or type so now I will need to buy a replacement. Not happy Jan :angry4: Any ideas? has anyone got one spare they are willing to part with or do I go to MB Spares and hope they have one?
Pete
the wagon uses different wire to the sedan and coupe :/

37 awg nichrome 80 (80% nickel, 20% chromium) Sedan/coupe

Wagon ??? I don't know, used it on my friends wagon and fuel gauge was out by half...

but here's a link to it anyway

https://www.amazon.com/uxcell-32-8ft-Ni ... mp_s_a_1_1

mathuisella
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Model you own: w123
Location: Brisbane, North side.

Re: fuel gauge

Post by mathuisella » Tue 28 Nov, 2017 12:06 pm

This guy will have the wagon fuel gauge signal sender unit for you :)
parts.JPG
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Pete49
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Posts: 300
Joined: Thu 09 Oct, 2014 4:42 pm
Model you own: w123
Location: Pt Augusta Sth Australia

Re: fuel gauge

Post by Pete49 » Tue 28 Nov, 2017 1:58 pm

Thanks for the post but I've ordered the wire from amazon as per your link so will wait and see how it goes. This close to Xmas will see delays in postage anyway. I have the low warning light working so I'll know when I get to reserve IF I forget to keep an eye on it.
I have found there are some changes to the W123 gauges so its a case of suck it and see I guess.
1978 W123 300D Maple Yellow
1981 W123 300TD Classic White (now sold)
1983 W123 280TE Champagne

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