How often should you change the differential oil? 2 different mechanics have told me don’t bother. It doesn’t need it. Yet it’s in the service book

 

2009 E350 4matic wagon 138K
I don't see an interval in my owner's manual maintenance schedule, but I just changed mine while I had the right-side axle out at 136K and the oil certainly was black. Heads up, if your car is like mine there is no drain plug for the front diff. I was looking underneath but it's on the right side. It is easier with he axle out but you can do it with it in, wheel off of course. Tt just takes a little flexible tubing (<1/4 inch if I remember correctly), a long plier of some sort to guide it, and a suction pump of any sort. Suck out the old, slowly pump in the new until it starts to overflow. Mine has a hex head type plug with washer which I was told to reuse by the dealer when I bought the fluid. Mine took 0.6 L. I had to sneak the hex socket wrench in with a combo of extenders with one of them flexible even with the axle out. Other than that, it's relatively easy to do. The fluid is of course thick so doing it on a warmer day than I had would help speed things up. I can't imagine why we wouldn't do it. Pics attached.

front of the car is to the left in pics

 

I dunno I do it pretty often at around the 80-100k range for the customers and the oil "looks" fine but if theres oil in there, it's doing a job and it's SUCH a cheap job to do yourself. I'd honestly just tell you to do it every 10 years on the non LSD cars. On the LSD cars 40k every time, 60k for front diffs of any kind.

 

My front transfer case is making some chattering noises on turns. I’m hoping the new oil chance to the case will resolve this. Anyone have this same noise?

 

80k-100k miles is a good window to replace all driveline oils (front axle, rear axle, transfer case). The transmission has a specified oil change interval.

 

I replaced my rear diff fluid when I did the transmission fluid. Super easy to do. At 70k miles I figured why not. It's cheap to do and takes maybe an hour to do.

-Nigel

 

Does the Rear have drain and fill plugs unlike the front of my '09 wagon?

 

My 09' e350 had both a drain and fill plug. Just buy new diff plusgs and the process is quite simple.


Believe I watched the video above before I did mine and it was the same exact process. EDIT: I did because I posted in his video asking for the diff plugs two years ago..lol

I also purchased this from amazon to fill the diff... Why I didn't buy this sooner blows my mind. I filled the rear diff up in maybe 4 minutes, compared to when I would use a combination of tubes and other crap for my truck which inevitably got diff fluid all over me and my floor...smh.

I went with the above model because other models similar only unscrewed from one end or the other. By unscrewing both ends I can ensure that it's clean throughout.

-Nigel

 

these have the easy squirt packs that fill the port with little drama

dealer link:
https://www.amsoil.com/p/severe-gear...vg/?zo=7236674

 

“Was Certainly black”, implying the oil was spent and needed replacement? , new diff gear oil is black too!

 

I would recommend to change it cuz mine was never changed out so When I did, it came out very thick syrupy look and black. Who knows if it was ever changed since I had the car since I got it at 65k miles and now I have 136k miles.

 

you can't tell when gear oil is bad except when it's very, very hurt. you can get away with it for a very long time. Since we're well past breakin thats probably the last time you'd need to do that on that car. BMW's ZF transmissions notoriously recommend you service it by the people who make them, although BMW does not. This is the origin of your distrust for the manufacturer's service recommendations.

Things about gear oil:
1) it always smells rotten, depending on what you use, sulfur, ash, and potassium are present in the anti-wear additives are perfectly natural and normal even when brand new. They're present in motor oil too, but much less of it so the smell isn't as pronounced until the oil is cooked and you're smelling the burnt versions of them.
2) it is always the same color, depending on what you use. The Shell/Castrol/Mobil Delvac 75w90 fills I'm very familiar with always look exactly the same coming out as they did going in despite me following the manufacturers recommendations for when these lubricants are past their prime.
3) it is always working and protecting your gears, until it's not, the gears are resting against a fluid film, not each other, the tolerance between the gears even accounts for this. As soon as you get metal to metal, stuff is going to start breaking pretty much right away, and/or welding.

i haven't seen a failure on a Mercedes specifically that wasn't just an undiagnosed fluid leak gone awry. You can pick up a slight noise if the fluid has been hurt, and its just good to keep the wear metals out of it. The LSD equipped AMG's however are a different scenario, way more heat and kinetic energy being dispered through the gear oil at all times. It thickens up over time too so it's a fuel mileage thing if you care about that.

The S class just had it's out at 110k, pretty much new looking hadn't thickened up too much although it still did, but factually it's past due.