W123 300D Fuel tank sender question

Stretch · #1 05-10-2010, 05:13 AM

Dear All,

I've had problems with a bouncing fuel gauge and the general solutions presented here on this forum are to check the wiring (grounding) and to change the sender.

I've just removed my sender and it was a bit dirty - so I'm now going to clean out the tank - but has anyone ever taken a fuel sender assembly apart to clean it?

There seems to be just two little holes at the base of the sender that allow the fuel level to get into the long sender tube. These hole could easily get clogged up.

When I removed the sender unit the float inside didn't rattle. After some shaking it now does. I assume it is getting stuck and a good clean will help.

A replacement part seems to be of the order of 200 euros. I don't want to pay that much. If it was say 20 euros I wouldn't be asking this question!

Any help will be greatly appreciated.

t walgamuth · #2 05-10-2010, 06:41 AM

I have never, but it looks like the bottom might unscrew.

fruitcakesa · #3 05-10-2010, 07:33 AM

There is a little nut on the bottom of the tube that is secured by a plastic "washer". I had to destroy that washer to unscrew the nut but I was able to tighten things back up later without the washer.
Carefully slide the "innards" out of the tube and all will be revealed,
Be very careful not to damage the 2 fine wires that the float slides on.

barry123400 · #4 05-10-2010, 09:29 AM

Instead of two hundred euros think junkyard part if it comes to it. A good cleaning may get you by. The wires for the contact are small and delicate so go easy. Blocked intake ports on the outer sender cylinder are not your problem.

Too much buildup on the wires, internal cylinder components and contacts inside are more likely. To attempt a cleaning just immersing the unit in a cylinderical cylinder filled with laquer thinner should dissolve all the gunk. Just lifting it up and down should flush the junk out after it disolves.

If it is too dirty just use some fresh petrol as a final drain wash. I doubt if anyone has done this yet to my knowledge but it will disolve the builup without taking the unit apart.

If the rheostat portion of the internal wiring is damaged then it will not. For all practical purposes you need another gauge assembley at that point anyways. It does sound like yours may still be in good condition.

With sendors the contact itself can wear badly on occassion as well over time. This has not been mentioned on 123 senders to my knowledge. On gas cars the buildup internally you have does not occur I believe.

Great ideal to clean the tank out at the same time. If you try the laquer thinner soak/wash let us know the results. I really think it would work in your case.

charmalu · #5 05-10-2010, 12:16 PM

I believe it is JEREMY5848 that has some pictures of replacing his in his w124. same procedure as the w123.
It may be in his thread/s that he has it taken apart.

Charlie

ImBroke · #6 05-10-2010, 06:07 PM

Some shameless promotion.
http://s199.photobucket.com/albums/aa26/t_goat69/Mercedes%20Repair/W123%20Tank%20Sender/

NoSparkNeeded · #7 05-10-2010, 09:19 PM

I took both of ours apart and cleaned. Mine was the worst. I repaired with solder. Be very careful of the fine wires guiding the float. Mine was corrodedbut I was able to clean and solder the joint so my reserve light would work. My wife's was just full of black gunk, that I cleaned up with carb cleaner. Both have been working. Mine for about 2 years, wife's about 2 months. Ifcareful, you can get these working again for pennies.

funola · #8 05-10-2010, 10:24 PM

The sender is made of premium material, beautifully put together and easily cleaned. Aluminum, stainless, plastic, nichrome wire, gold plated contacts. Nothing to rust. Everyone I've fixed has been gunked up with black algae. Use long nose pliers on the plastic washer cup and remove it with the round nut in it. Then remove the plastic and stainless bottoms. Next slide the aluminum housinsg tube straight out. Be careful not to damage the 2 fine nichrome wires. Use a caustic cleaner (potasium hydroxide) such as Purple cleaner in a tall plastic cup and submerge the sender one end at a time (wear gloves unless you want to lose your skin). Use a small parts brush and poke at the crevices to loosen the gunk.(poking is less likely to break the fine wires than brushing). Rinse in hot water. The algae will dissole revealing gold plated contacts. If there is dried algae on the nichrome wires you have to get it off. The float has gold plated wipers which connect the 2 nichrome resistance wires together and its resistance change per float level. Repeat the cleaning till it's spotless. Don't leave aluminum in the caustic too long (more than a min or 2) it will dissolve. After hot water rinse, let dry in the sun then reassemble. Should be good as new.

elrey · #9 05-10-2010, 11:15 PM

Quote:

Originally Posted by NoSparkNeeded

Be very careful of the fine wires guiding the float.

x2 to this. When i was trying to fix my sender i snapped one of these wires. It was such a pain trying to fix the wires i just gave up. I am ashamed to say my sender is now FUBAR.

funola · #10 05-10-2010, 11:30 PM

If the break is where the wire is attached and not in the middle, it can be soldered back. If anyone need a sender, I have a good unit (just cleaned).

charmalu · #11 05-10-2010, 11:32 PM

OK, here is my shameless promotion.

DIY w/pix -- W124 fuel sender disassembly/cleaning/testing

I know this is a W124, but the same set up.

I would have looked this up earlier, but wife said we had to get going.
my story, and Iam sticking to it

.

Charlie

Stretch · #12 05-11-2010, 04:09 AM

Quote:

Originally Posted by charmalu

OK, here is my shameless promotion.

DIY w/pix -- W124 fuel sender disassembly/cleaning/testing

I know this is a W124, but the same set up.

I would have looked this up earlier, but wife said we had to get going.
my story, and Iam sticking to it

.

Charlie

Great story - great link - thanks a lot.

I was going to just try the soaking in solvent suggestion but now I'm curious to see if my slightly different sender is indeed much like the W124 one... I'll post some pictures is it all goes well - otherwise I'll say no more if I've had to find a replacement!

Stretch · #13 05-11-2010, 04:12 AM

Quote:

Originally Posted by ImBroke

Some shameless promotion.
http://s199.photobucket.com/albums/aa26/t_goat69/Mercedes%20Repair/W123%20Tank%20Sender/

Sorry I missed this one before replying to Charlie - nice photos I see that indeed they didn't change the design much between the W123 and W124 models (no great shock there then)

Stretch · #14 05-11-2010, 04:16 AM

Quote:

Originally Posted by funola

The sender is made of premium material, beautifully put together and easily cleaned...

...Don't leave aluminum in the caustic too long (more than a min or 2) it will dissolve. After hot water rinse, let dry in the sun then reassemble. Should be good as new.

I don't see much sun where I live - but I'll put it on a radiator to dry!

Good clear instructions - thanks a lot