How to Repair Your Fuel Sending Unit

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[@lbowsk]

On my 85 300CD, the gauge would typically show FULL when I filled the tank and would then hang up at about 3/4 tank. The ODO would show another 100 miles going by with zero change on the indicated fuel. As Pierre states, the float MUST be free to slide up and down those wires. Mine had a small accumulation of hard crud on them. I carefully removed it using a very sharp blade on an exacto knife. That was 30K miles ago. Its been perfect ever since. Easy job.

[@ekipe]

I think this was one of the most useful videos on the youtube for classic Mercedes lovers!! Thank you Pierre.

[@mercedesclassicswithpierre1753]

glad you enjoyed it

[@sebaaaa56]

@@mercedesclassicswithpierre1753 Pierre, do you have any idea why my R107 300SL fuel gauge is pessimistic? I get the reserve light on when there's still about 20-22 litres of fuel left in the tank.

[@mustafaabdulhafeez3992]

Thank you so much

[@burundib1352]

Thanks for this video! I bought a tank for my 1967 280SE and I'm glad I watched this video. Now I know how to prep the fuel sending unit for installation. Thanks again!!!!

[@secondopinion6654]

Crucial tip for wire issues. The wires have to run through the little guides on the plastic slider in a mild S-shape. If the wires run straight along next to the slider you will not get a reading.

[@bryanharter4850]

Thanks Pierre! Good stuff!

[@MrRjnr]

I just did this today; very straight-forward & well worth it! hard time getting the rear seat bottom to latch in though

[@northbeachfilms]

thank you! these are also easy to remove from the w123 models. so nice of you to create such a helpful video for us to learn from and enjoy. have a great day. cheers.

[@mercedesclassicswithpierre1753]

We really appreciate you North Beach Films for viewing our videos and leaving a comment. I tried to read as many as I can and take your responses for consideration on future videos. Thomas Polk KZbin Creator.

[@thegreenviking1422]

this was a very helpful video. thank you Pierre. Have the same sender on my W124 200 1998. got to take it apart now,

[@ImpalamansGarage]

Doing a tank job on my 300SD now. Thanks for the tip!

[@hakosama]

Thanks for the video. It was very helpful. I pulled mine out and cleaned it. My problem was that one of the three wires was not making contact with the float. Re-routed it and it works great. I thought I would have to buy a special tool to take the sending unit out of my 1982 -300SD but was able to get it out using some large channel locks.

[@klwthe3rd]

Pierre your videos are getting better and better. Unlike some people I know, that advice came free of charge. I would love if you ever had a repair seminar day at your shop. Have a one day charge per attendee and just give everyone there a general overview of the most common problem and possible fixes for the chassis 123, 124 and 126. 108 & 109 if there is any interest.

[@mercedesclassicswithpierre1753]

we are looking at doing one in april. thank you again for the positive feedback.

[@jackflanagan4971]

Happy to hear of a general tech session most importantly to meet you but equally important to "rub shoulders" with other M-B owners whose experiences would be great to hear for our consideration in care & maintenance of our "gems". Internet forums are ok but in-person networking is best, especially since some MBCA chapters mostly seem do "eat & run" sessions w/o time to discuss tech sessions/ how-to's. That's the key to MBCA/brand loyalty!

[@klwthe3rd]

@@jackflanagan4971 I couldn't agree with you more. Forums have their place and are great for what they are, swapping information. But having the opportunity to meet up, discuss openly and show by visualization is so much more appealing to me. I look forward to the event.

[@louisfritz2889]

Great I,m going right to the garage and practuce what I just learned at video, gets right to the point.

[@unpob]

Thank you Peter

[@stevenbarnett6614]

Great information. I have to do this on my 300SD. Thank you Pierre.

[@mercedesclassicswithpierre1753]

good luck the one for the 300sd is not back in production yet either

[@christopher6161]

thank you pierre

[@lux2j]

Awesome input

[@THIRSTYGUMS]

just the info I needed today!

[@mercedesclassicswithpierre1753]

awesome!!

[@sportsmansparadice42]

Ok guys before you purchase a new fuel sending unit try and clean the electrical connection on top of the unit first. Don't make the same mistake I did, and purchase a new VDO sending unit which didn't solve the gauge Fluctuating issue. I took the old one apart, and cleaned it up well put it back together and used a 220 grit sand paper to clean the electrical connection on the sending unit. It works perfectly fine now.BTW it's a 1995 E320

[@angeldelcarpio1406]

Thanks 🙏 a million bro

[@davidpettifer1541]

Getting stabbed.😂😂😂😂😂Got a rusty shaft 😂😂😂 Incredibly amusing and informative. Thankyou.

[@pinzgauernorcal]

Yes very helpful thanks

[@volkmarmaleika1623]

Thank You for your informative video. Mine is a 74 230 and the fine wire broke. Hope I can route that wire correctly. Also mine has a 3rd wire and looks like to guide the float. I am going to use some new cooper wire which is the sending unit. Let you know if it works. VW

[@anthonysimmons1673]

Thank you!!!

[@JoeGomez1]

Thank You for the Info

[@mercedesclassicswithpierre1753]

you're welcome!

[@pinzgauernorcal]

does the wire snake through the contacts in an "S" or just ride them on the side?

[@solomanlam1270]

Hi, can you tell me the size of the nut that’s holding the fuel sender on a 86 420sel W126 chassis ! Thanks.

[@luisarturogarciaarmijo9117]

excelente

[@robertsteffen7597]

Pierre how do you remove a fuel level sensor from a 1973 450SL that was one that was epoxied in place?

[@saintpreferred4159]

Excellent.

[@mercedesclassicswithpierre1753]

glad it was helpful!

[@jensenhealey907efi]

Is the fuel sending unit the same on a 1993 W124 wagon? If it is, how / where do you access the fuel sending unit on a W124 Wagon?

[@mahlonpaul4568]

Wat about the wires Bru? Aren't they sup to be running thru the contacts on the slide? Which way?

[@ItsTimePictures]

$280 is really not all that much money when one considers what things cost these days. Interesting and informative video. Instructional vids like this one are huge for the DIYer.

[@mercedesclassicswithpierre1753]

It really isn't...but some of the senders are not available yet, like the one for a 126 sedan

[@CozannHernandez]

I have a 560 sel and the gas gauge just quit working! It is on empty! But the tank was filled. If it shows empty without a light does that mean no power to the gauge or no ground or something else

[@emilianogualdieri4930]

Hey there. Besides of the hole at the top of the pipe is there another one on the bottom? I took my sender out but I can't figure out how the fuel goes inside the pipe if it doesn't have a hole in the bottom. I'm confused, don't know what to do

[@robertsteffen7597]

Pierre you have failed to respond to my question on how to remove the fuel sensor in a 1973 450SL that was one of the units that was epoxied in place. Please help me out.

[@charlesrussell7090]

I have a '94 e320 convertible and under the instrument cluster there is a box mounted with a dial on it with "I" on one end and "O" on the other. I can't find anything to tell me what this is. Can you help me?

[@chuckho8950]

what are the spec on the wires for the unit.

[@faizrahman7671]

thanks for the great video as always my sec may have an issue with its sending unit. The reserve light will go on with 2 gallons left as it is supposed to do but the gauge needle still hangs around the middle rather than the empty area. when removing the sending unit, are there any precautions needed. Does it matter if the tank is empty or has gas? My car is an 85 500sec thanks

[@mercedesclassicswithpierre1753]

you don't need to drain the tank...the unit comes out of the top. the resistor wires are very delicate, so when you disassemble and clean the unit treat the wires inside the sender with the utmost care. your issu e might actually be in your fuel gauge. IS the fuel gauge the original one supplied with your car?

[@faizrahman7671]

@@mercedesclassicswithpierre1753 thanks. I'll put this on my long list of projects for the sec... In meantime I'll watch the light....can't watch the trip because those gears broke the other day too

[@klwthe3rd]

Pierre, If you want to be proactive in regards to your fuel sending unit on a W126 sedan what can you do? I know on the W126 you have to remove the rear seat to get at the unit but how can you tell if it's going bad?? Nobody wants to wait till it fails so I wanted some tips as to know when your unit might be ready to go out on you. Can you tell just from looking at it once it's removed from the tank?

[@mercedesclassicswithpierre1753]

good idea....thank you

[@MarkInLA]

Negative on using a file to clean the shaft ! what you'r missing is the explanation of how the 2 thin wires run over one and under the very tiny brass tongues on either side of the float (not plunger!). Those wires get out of place here and need to be re-positioned to run over one and under the other of 2 tongues on each side..This is an extremely delicate re-seating, but doable with patience.. Also these same wires get snagged on the white nylon parts on bottom of the float.. They need to be freed and then running in the center of the square holes in the nylon. One will probably be good, so you will see how IT runs.. This too is extremely delicate. With them properly strung, the float should easily slide up and down the center shaft..And yes, clean out the inside of the tube and be careful that you get its notch seated onto the main top-cap witch has a matching male part it mates with.. Don't over tighten the little rubbery nut at the tube bottom.. Your gauge on the dash should now be reading properly. If not, try redoing the job..Then, if no go get one from another Benz at a Pick your Part for, what, $10.00 ?! ... Mark, Los Angeles PS. This could very well not be the problem. Could be at gauge or wiring to/from float....

[@mercedesclassicswithpierre1753]

Mark, thanks for the insight What do you reccommend to clean the shaft if the plunger is binding on it?

[@gordonelza]

Just found your site . Any idea where I could buy a 85 300d air filter housing California car Thanks Tom

[@mercedesclassicswithpierre1753]

that's a tough find....email me at [e-mail]...maybe I can help

[@adelkheir]

Pierre I have a '79 w123 230 carburated and the fuel guage only reads until the tank is half full and then completely drops to zero when its less than that. sometimes it occasionally works when hitting a bump or just tapping on the sending unit itself. could this be a matter of just cleaning the internals ?

[@mercedesclassicswithpierre1753]

Hello, adelkheir and thank YOU so much for your question(s), we want to answer you as quickly as possible. By signing in our Patreon www.patreon.com/thomaspolk page and making a donation of $10 your are assured of a 24 hour email response from Pierre. If you are already a $10 member please mention along with your question.

[@mercedesclassicswithpierre1753]

yes, i would start there. you likely have a broken wire, which could cause the issue.

[@metalmalitia23]

Did this on my w124 and pretty much the same principle applied. I just can’t get the small nut to start threading back on though.

[@mercedesclassicswithpierre1753]

you can use any nut that has the same thread.

[@eliezerlebron5589]

I actually had to work with my sending unit a few months ago. The wires on my unit are broke. I purchase a used one on a near by yard, but would love to fix the original. Any good ideas on how to replace and fix those wire? Thank you in advance, great video by the way. (380 SEC 1983)

[@hellkell8693]

Measure the resistance of the wire per unit length and find the same resistance wire online.

[@evgenirafalson3041]

Is it the same sending units for gas and diesel?

[@whozat2008]

Did you ever find out if there’s a difference? The unit for the W460 G wagon is no longer available so I’m attempting to modify one from a W126 CD to fit my W460.

[@Bauerofficial]

the very thin wire, that's 0.05 mm thick is the constantan wire that shows you if you are on reserve. it has a resistance of 292 ohms. it's usually not available in hardware stores as its resistance is very high.

[@mercedesclassicswithpierre1753]

yes, all of this is on the premise that the wire has not snapped in half

[@Barola007]

I have a constant reserve light on the dash gauge after cleaning sending unit. The amount of fuel shows correct info just the reserve low level fuel light bulb is on all the time. Any suggestions?

[@robertsykes3242]

Hopefully its the same principle on the 115.

[@mercedesclassicswithpierre1753]

it is

[@scottritchey7492]

Is there a fix if the wire is broken?

[@mercedesclassicswithpierre1753]

if the end comes detached you can solder it back on, but if the wire snaps, which is actually very rare, then I have not found one yet

[@scottritchey7492]

@Afzaal Khan.M: Many thanks. About a decade ago, I broke the wire on the gauge of my 300SD when I lost my grip while cleaning it. I had gotten load of really bad fuel somewhere with so much crap that it plugged the strainer at the bottom of the tank. The whole tank, including the gauge, was a mess. I blasted the crud out of the tank with a pressure washer and then dried it with a shop vac on blow (took 2 days). I managed to solder it somehow (don't recall how) but I will probably need a new wire or gauge if I break it again. Some years earlier, the OE gauge wire broke for no reason and I replaced the gauge; they were only about $100 then. So I appreciate the info.

[@kevinpantera4429]

250c has 8 little bolts to screw out. Gauge not working. Need to drop tank and get at that. Should not be too bad.

[@unpob]

I mean Pierre.....

[@mercedesclassicswithpierre1753]

no worries, you are welcome

[@jamesrich3190]

Yeah, I don’t wanna get stabbed… 🔪😅