Unknown Age MB Differential Oil

[JHZR2]

My new to me 1993 MB 300SD kind of fell into my lap. I bought it for the engine and transmission but it’s growing on me. I decided to change the differential oil after a 300 mile trip where the car ran beautifully. The car has 291k miles on it.

This car has the anti-slip differential option. It was a $775 option in 1993. It has a hydraulically and computer controlled LSD that can adjust clutch lockup between 30-100% based upon conditions. No idea how well it works… no dummy lights come on for it though the dummy lights work.

I anticipated that it would be dirty. In reality the fluid came out decent in color and smell.

The fluid came out ok. The plugs were filthy though.

The drain plug had a heavy coating of sludge on it despite not being a magnetic plug. The fill plug also had a decent coating of black junk but nowhere near as thick.

I refilled with Walmart super tech conventional 80w-90 with lubeguard limited slip additive. I didn’t want to go expensive when I figure I’ll probably be draining this in a year or so to get out any other junk. Then I’ll probably go 75w-90 syn.

 

[Lubener]

Probably original. Sounds like you have a good plan. Next time I would remove the diff's cover (if you can) to clean out that sludge.

 

[JHZR2]

Probably original. Sounds like you have a good plan. Next time I would remove the diff's cover (if you can) to clean out that sludge.

At 291k miles I’d hope it had fluid changed at some point… certainly from a time perspective it may have been a very long time… I was glad to not see signs of moisture.

 

[JohnnyG]

Are you SURE those aren't magnetic plugs? German engineering can be pretty tricky at times.

 

[Hall]

Are you SURE those aren't magnetic plugs? German engineering can be pretty tricky at times.

They have to be magnetic just from the way 'stuff' is collected on them. The magnetism may be small enough that sticking another magnet to it doesn't react but for tiny metal shavings, it's strong enough.

 

[JHZR2]

Are you SURE those aren't magnetic plugs? German engineering can be pretty tricky at times.

No sign of a magnet or magnetism. Ive bought pipe plugs with magnets for some of my MB diffs because of that,

They have to be magnetic just from the way 'stuff' is collected on them. The magnetism may be small enough that sticking another magnet to it doesn't react but for tiny metal shavings, it's strong enough.

The sludge need not be magnetic. The LSD clutches can also shed material.

 

[Lubener]

At 291k miles I’d hope it had fluid changed at some point… certainly from a time perspective it may have been a very long time… I was glad to not see signs of moisture.

The differential is probably the toughest component on the automobile, it can tolerate the neglect. With the appearance of your oil, the accumulated sludge on the plugs, my bet is it's original.

 

[Wolf359]

Why not just get the MB fluid? It probably doesn't hold much, probably anyway from a half a quart to two quarts so one or two bottles even at $20+ a quart isn't that big a price difference. I'm not sure about that particular model, but I know on others, some claimed worse gas mileage using aftermarket fluids as it was thicker than MB specs. I would just look up the right fluid in EPC and order it from online MB dealers or aftermarket vendors that sell MB fluids.

 

[JHZR2]

Why not just get the MB fluid? It probably doesn't hold much, probably anyway from a half a quart to two quarts so one or two bottles even at $20+ a quart isn't that big a price difference. I'm not sure about that particular model, but I know on others, some claimed worse gas mileage using aftermarket fluids as it was thicker than MB specs. I would just look up the right fluid in EPC and order it from online MB dealers or aftermarket vendors that sell MB fluids.

Because for one thing I didn’t know how bad what I drained would be, so I wasn’t going to sink that much money in for the first drain.

And besides that, the fluid, including the Fuchs brand is NLA at my online parts places. Dealers might have an OE part, or may use an aftermarket fluid themselves.

I’m failing to see how what I used is inconsistent with the MB recommendation from my 1993 owners manual… it’s true that the updated 235.7 spec is 75w-85, but me running an 80w-90 with LSD additive seems consistent enough with the owners manual. After flushing this I might consider the redline 75w-85 which claims it meets the spec.

 

[Wolf359]

Because for one thing I didn’t know how bad what I drained would be, so I wasn’t going to sink that much money in for the first drain.

And besides that, the fluid, including the Fuchs brand is NLA at my online parts places. Dealers might have an OE part, or may use an aftermarket fluid themselves.

I’m failing to see how what I used is inconsistent with the MB recommendation from my 1993 owners manual… it’s true that the updated 235.7 spec is 75w-85, but me running an 80w-90 with LSD additive seems consistent enough with the owners manual. After flushing this I might consider the redline 75w-85 which claims it meets the spec.

What's the price difference between the redline fluid and the MB fluid? While redline claims to meet the spec, it's not on MB's approved list.

Mercedes-Benz Betriebsstoff-Vorschriften

Die Mercedes-Benz Betriebsstoff-Vorschriften zeigen eine Übersicht der Anforderungen der im Fahrzeug benötigten Betriebsstoffe und der empfohlenen Produkte. Betriebsstoffe sind alle zum Betrieb eines Mercedes-Fahrzeugs / Aggregats erforderlichen Flüssigkeiten bzw. Schmiermittel z.B. Kraftstoff...

bevo.mercedes-benz.com

 

[JHZR2]

What's the price difference between the redline fluid and the MB fluid? While redline claims to meet the spec, it's not on MB's approved list.

Mercedes-Benz Betriebsstoff-Vorschriften

Die Mercedes-Benz Betriebsstoff-Vorschriften zeigen eine Übersicht der Anforderungen der im Fahrzeug benötigten Betriebsstoffe und der empfohlenen Produkte. Betriebsstoffe sind alle zum Betrieb eines Mercedes-Fahrzeugs / Aggregats erforderlichen Flüssigkeiten bzw. Schmiermittel z.B. Kraftstoff...

bevo.mercedes-benz.com

I don’t know the price of the MB fluid because at least all the online parts places I buy from say it is NLA. Same places say the Fuchs lube is NLA. Amazon seems to have some of the Fuchs lube for $32/L. Worth it especially when I’m trying to flush out dirt and sludge? Dubious.

We’re not talking ATF in some specialized transmission. Sure; the w140 was a $70-100k+ car back in 1993, and an advanced car for its time, but that doesn’t mean every last attribute was.

As noted, I’m following my owners manual. I’m compliant with that, and it’s far better to have new fluid than old. LOTS of folks put redline fluid into euro differentials. I’m not the biggest fan of redline but it meets the (updated) viscosity range and is suited for LSDs.

There is no firm indication that the MB lube is anything overly special. As I said, after a round or two flushing it with the cheap stuff I may go to the MB fluid. Or not. I’ll be over 300k miles at that point.

 

[Hall]

Call a dealer parts counter to get the price and ask if they have it in stock for the "M-B" gear oil. When they tell you it's no longer available, ask them what they sell over the counter or what the shop uses. I bet you'll find they're using some parts-store-branded gear oil.

 

[JHZR2]

It’s more time and effort than I’m interested in. This isn’t hard to understand. I posted what my owner’s manual indicated needed to be used, and I used that.

I’m not terribly interested in shifting from a 90wt to an 85wt. I’m not going to call all over the world for a fluid that won’t make a difference.

If this was a later model transmission or something you bet I’d be all over the dealer fluid. Just like I run Honda specific ATF and PSF in our Honda cars. For this it is not something I’m looking to do. I’ll check back at 400k miles to make my point.

 

[Hall]

It’s more time and effort than I’m interested in. This isn’t hard to understand. I posted what my owner’s manual indicated needed to be used, and I used that.

My point was that odds are you can confirm that the gear oil you used will be just fine and that the dealers aren't using anything special either.