Just over a year ago, I drained and refilled the differential on my '84 190D-2.2. The old fluid that came out was a shade darker than the new fluid, but nothing out of the ordinary. The new gear oil that I refilled it with was yellow and clear (like the color of cooking oil).

Last night, I decided to give the car a general inspection to see if anything needed attention. When I checked the differential fluid level, the filler plug was covered with some sort of black slime. I stuck my finger inside the filler hole to see if the differential was full (it was), and the fluid inside was extremely dirty; it looked as though more of the same black sludge was blended in with the fluid.

The fluid has only been in use for about 18 months, or maybe 15,000 miles, and the fluid that was in there before wasn't dirty like this.

I intend to replace the dirty fluid ASAP, but I would like to know how and why it became so dirty so quickly. Where did this black sludge come from? Is there something else I should be looking at?

As always, I really appreciate any help or advice that you can offer!

Thanks!

__________________

1989 250TD Wagon 5-speed, 160,000mi ::: Dark gray metallic / black cloth
1984 190D-2.2 5-speed, 287,000mi ::: Silver-blue metallic / black MB-tex ::: SOLD

It could be just dirt but to make sure, I'd take the cover off and see the magnet there. Could be that you went thru someplace wet or dirty and dust got into the vent or something.

__________________
01 Ford Excursion Powerstroke
99 E300 Turbodiesel
91 Vette with 383 motor
05 Polaris Sportsman 800 EFI
06 Polaris Sportsman 500 EFI
03 SeaDoo GTX SC Red
03 SeaDoo GTX SC Yellow
04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow

Best guess:
Incompatible oils???
Vent plugged???
Bearing going bad = burning fluid???

__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

But if the bearings are going bad, won't the magnet pick it up? Also, won't it howl or make noise? Mine did when they started to go south.

__________________
01 Ford Excursion Powerstroke
99 E300 Turbodiesel
91 Vette with 383 motor
05 Polaris Sportsman 800 EFI
06 Polaris Sportsman 500 EFI
03 SeaDoo GTX SC Red
03 SeaDoo GTX SC Yellow
04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow

Magnet will only pick up ferrous material.
Heat generation from bad bearings breaks down the oil first.
If you could feed enough fresh clean oil to the a bearing that is going bad, it would last years longer, and cost thousands in oil.

The diff. is making a very slight whine; it's certainly not very noticeable though (it's the kind of noise I can hear but my wife can't ). Right now, it doesn't sound like it's anything abnormal.

The roads have been filthy around here, lots of sand and salt and slush, and when I wash the car, I spray the underside to clean off salt; maybe something worked it's way inside the diff. housing through the vent.

From what you've said, it sounds like I should:

1) check the condition of the vent
2) refill with fresh fluid
3) keep an eye (ear?) on it for any abnormal sounds that would indicate bearing issues

Anything else?

Do you remember if the cover can be taken off without removing the differential from the car? I'd like to clean out some of the sludge before I refill, but I can't remember what the underside of the car looks like right now.

Thanks for the help!

__________________

1989 250TD Wagon 5-speed, 160,000mi ::: Dark gray metallic / black cloth
1984 190D-2.2 5-speed, 287,000mi ::: Silver-blue metallic / black MB-tex ::: SOLD

Sounds like a bearing going bad. Any whine is abnormal. If you're going to go in there you may as well replace the carrier / pinion bearings as it may do a lot of things but get better won't be one of them.

__________________
1982 Mercedes-Benz 300CD
1982 Mercedes-Benz 240D - stick

What gear oil did you use? I don't recall seeing a "yellow and clear" gear oil usually they a pretty dark to start with. Does the oil have a burned smell to it?

__________________
Bill Reimels
Now down to one:
1972 300SE 3.5 W109 (Euro delivery)

Mobil 1 gear oil will turn dark very quick on the first fill, it likes to clean up the dirt and sludge and everything else...

123c's comment sounds like it might be on target. Maybe your new gear oil is a more effective cleaner than the old oil was and is loosening up deposits the old oil left behind.

Thanks for the comments & suggestions. The fluid that I put in last year was SAE 80w90 gear oil. I still had some left from the original bottle I used, so I've attached a 'before and after' photo showing the original gear oil and the oil that came out of the differential. Yuck!

I refilled with semi-synthetic 75W90 gear oil, and I'll check it in a month or two and see how that works...

Attached Thumbnails

 

__________________

1989 250TD Wagon 5-speed, 160,000mi ::: Dark gray metallic / black cloth
1984 190D-2.2 5-speed, 287,000mi ::: Silver-blue metallic / black MB-tex ::: SOLD

Ow...yuck....thats mighty dark on the right....

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

What brand and weight gear oil is correct for rear end, I need to change mine.

__________________
1982 300SD Light Blue
2002 Honda Accord SE
1974 Toro Wheel Horse Tractor
2000 Toyota Tundra Pickup

So would it then be a good maintenance practice to change it more frequently?

Or perhaps to change it a couple of times in quick succession in the case of an older car in which it may not have been previously changed...?

- Patrick

__________________
1982 240D. 198k, Marine Blue/Blue, 4 Speed, Crank Windows, No Sunroof, No Rust, No Oil Leaks
2001 TDI. 197k, Lagoon Blue/Black, 5 speed, Chip, G60/VR6

With that theory then perhaps you should try changing it and observe.

__________________
01 Ford Excursion Powerstroke
99 E300 Turbodiesel
91 Vette with 383 motor
05 Polaris Sportsman 800 EFI
06 Polaris Sportsman 500 EFI
03 SeaDoo GTX SC Red
03 SeaDoo GTX SC Yellow
04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow