Fuel Sender 85 300D- Cleaned (Pics) - PeachParts Mercedes-Benz Forum

tobybul · #1 05-26-2007, 04:33 PM

Here's some pics of fuel sender that I cleaned today. Its the unit in the fuel tank accessed by removing the First Aid Kit compartment right behind the rear backseat. My reserved fuel light has been going on/off.

Dirty unit. Look at the really black lower part.

Another view.

Wiped it with paper towel and later sprayed it with brake cleaner to remove more gunk.

Generously sprayed inside with brake clean and carefully shook unit. Drained it out thru weep hole and lots of blackish solids came out. Did this 3X until solvent was clear. Then blew it with compressed air thru weep hole to dry it out and reinstalled.

Carson357 · #2 05-26-2007, 04:41 PM

you should have removed the little nut on the bottom using a small pair of pliers and dissasembled the unit and clean it thouroughly, inside is probably a lot more sludge, it collects at the bottom, it isn't too complicated, just be sure to be gentle with the wires inside.

TheDon · #3 05-26-2007, 06:55 PM

yes, the small nut on the bottom is a pain to remove without plier.. Do like carson said. I did mine and my guage read alot more accurate than before. Their was alot of crud in there. Be careful with the guide wires

Stevo · #4 05-27-2007, 12:37 AM

I did the one in my 79 last week. It was working but seemed to be "hanging up" a little when the tank got low. When I opened it the lower end was really caked with black goo. I did another one that was not working at all. The thin wire was broken at the lower end. A friend held it and I re soldered it, its still working

tobybul · #5 05-27-2007, 12:50 AM

Ok, I'll take it out again tomorrow since its fairly simple to do. I wondered about the "thing" at the bottom. Didn't look like a nut so I didn't attempt to mess with it. The reserve light still comes one so it looks like I didn't clean it well enough.

One thing I learned was when lifting the unit out of the tank, you gotta do it very slowly so all fuel in the unit drains out first back in to the tank. Otherwise, its squirting everywhere.

JimmyL · #6 05-27-2007, 01:00 AM

Here is the fun part you missed.....

If the light comes on a lot, I suspect it is either stuck down at the bottom, or a wire may have broke/come loose. Careful, they are thin.....

Stevo · #7 05-27-2007, 11:14 AM

Quote:

Originally Posted by tobybul

Ok, I wondered about the "thing" at the bottom. Didn't look like a nut so I didn't attempt to mess with it.

That little nut is "captured" by, what looks like, a little piece if plastic hose which I pulled away with plyres. I put the nut back with blue thread lock, dont know if thats the correct procedure but thats what I did.

tobybul · #8 05-27-2007, 05:30 PM

Now am wondering if this unit is this bad, the strainer at the bottom of the tank probably looks the same or worse.

BrierS · #9 07-27-2008, 02:48 PM

My '84 had the empty to 1/4 full fuel gauge syndrome so I searched, followed what others have done and found the float shaft had rust. Of course the rust would not allow the float to rise beyond the point corresponding with the 1/4 mark. Gentle work with emery cloth, some PB Blaster, thorough rinsing, reassembly and works great. This vehicle had not moved for ??? so it certainly made sense.
Steve

yellit · #10 07-28-2008, 12:36 AM

A Harbor freight ultrasonic cleaner with a little Simple Green works wonders on these after getting them apart...just be real easy with the fine wires.....check for corrosion around the bottom contacts & wire attachment solder points...mine had high resistance rust that was throwing the whole unit off....had to re-solder..all ok for now....

If you are real careful you can gently bend the tiny contact leaves on the float to get a better grip on the wire....two on each side....delicate touch needed there...

pawoSD · #11 07-28-2008, 02:11 AM

The next time I really run down my fuel tank I am going to have to remember to do this.....my reserve light doesn't work and the gauge never reads accurately....just from Full to half....then it will fall abruptly to 1/4 from 1/2 after another 100 miles.....then go a little further and it lays at R....but no reserve light....mines probably full of sludge.....

yellit · #12 07-28-2008, 02:37 AM

Another good test is to attach the female connector to the unit while it is out of the aluminum tube ( being careful of the thin wires) and slide the float up and down by hand (out of the tank of course) while watching the fuel gauge for smooth tracking and reserve light function at bottom of float travel....Ign. key in ACC position or with the engine running
You must kneel in the seat facing backwards to manipulate the float while holding it in the rear shelf area unless you want to use jumper clips for a little more slack....

Found a couple of dead spots along the float wire path but cleaned them up with fine emery paper.....
Nice way to test unit without the mess after repairs......

pawoSD · #13 07-28-2008, 12:33 PM

I noticed in the pic that you're using NAPA brake cleaner.....the AutoZone stuff is WAY more powerful....and has a more controllable spray tip. (So you don't empty the whole can in 5 seconds) Not to mention you get 14oz instead of 12...for less $$

whunter · #14 03-07-2010, 04:09 PM

Quote:

Originally Posted by JimmyL

Here is the fun part you missed.....

If the light comes on a lot, I suspect it is either stuck down at the bottom, or a wire may have broke/come loose. Careful, they are thin.....

The drain hole is in the black plastic end cap !!!

* When this hole is totally plugged, the sender will read FULL when the fuel tank is EMPTY..

** When the drain hole is partially plugged, the sender is extremely slow to change/react, most notable (key on) during fueling from EMPTY to FULL.
I have seen examples of this reaction issue, from three minutes to one day to reach the correct reading...

Scott98 · #15 03-07-2010, 05:05 PM

This is a great post. These sending units are around $200 so knowing how to take one apart and fix it yourself is a huge help. Mine just stopped working (indicating full all the time) so I will certainly disassemble mine now.

Scott