As posted in my introductory thread I could not find any evidence of the differential oil having been changed in my 8 year old 20.5k mile SL63, so I decided to do it myself. Per the manual, AMG R231s with the limited slip differential are to have the fluid changed at 2000 miles and thereafter every 40k miles / 4 years.

There are a few threads on differential fluid changes so I am not breaking new ground, but there are not many pictures and some contradictory information on fill plugs, so I thought I’d document my experience.

Guided by the Mercedes BeVo site, I bought 2 liters of . Note that non-LS differentials use a different oil specification. I also purchased a couple of hand pumps, worked perfectly.

I raised the car on my 4 post lift. Boy that thing has sure come in handy the last several years!


The fill plug (always remove this first!!) is on the driver side of the differential housing and the drain plug is on the passenger side. Both are 19mm conventional hex plugs, at least on my car, as I have seen several other sizes mentioned in other posts. The entire differential case, including both plugs, is painted in a gray finish. When applying torque to remove the plugs, this paint chipped - which led to momentary panic as I thought that the plugs were soft aluminum and were being destroyed by my socket wrench. But no, the plugs are steel and it was only the superficial paint layer that was getting chewed up. Two takeaways are (1) the pristine condition of the plugs most likely was proof that the oil had not been changed before, and (2) some internet sites state that you should have new plugs on hand for this change - that is unnecessary IMHO as it is hard to damage the plugs beyond the paint layer.

The fill plug - view shows driver (left) side of differential housing with front of car to the left.


The drain plug on passenger (right) side of differential housing - front of car to the right.



One of the removed plugs showing damaged paint layer but perfectly fine steel plug


For inspection purposes, I drained the oil into a shallow pan. It seemed like a dark suspension, but not gritty to the feel. On a whim, I dropped a strong bar magnet into the pan, and immediately there was a perfect magnetic field visible. That told me that there was ferrous material suspended in the oil, but after swirling the oil all around the magnet and letting it sit for a while, there was no gritty / granular material on the magnet at all. So not really a problem.



To fill up the oil, I used the pump mentioned above. It worked like a charm. The stated capacity of the differential is 1.2 liters. I used a couple of squirts of clean oil initially to “flush” the housing with the drain plug still open, and a fair amount was lost in spillage, etc., so I used a total of about 1.6 liters.


I used Teflon tape on the plugs and tightened them to the standard German DIY spec of “gutundtight”.


In summary, an easy DIY. Hopefully these pictures help someone else.

 

Thanks for the quick and easy tutorial.

Why the teflon tape? Were you expecting leakage? Those plugs look like they had some deep threads, probably way into the housing.

 

I’ve always used Teflon tape on all the plugs of every unit in my collection as cheap insurance against drips. Why button up a pleasant job only to find drips on the concrete a few days later. At that point you have to lift the car and drain the new fluid all over again to re-install the plug. Initially wrapping the threads with the tape only takes 5 seconds so why not?

 

GM recommends Liquid Teflon Pipe sealant on their differential plugs. I’ve used this successfully for years on all my drain plug pipe threads. It’s easier to apply and more durable than tape ( Permatex also makes a cheaper version if you search). It’s amazing how a thick oil can weep…
Permatex

GM

 

Why Teflon tape? Well metal threads don’t generally seal by themselves. Many plugs e.g. oil drain plugs have straight threads and then seal with a softer metal or elastomeric washer against a plug flange. These things here are like pipe threads in that they have a slight taper and no flange. Indeed I’ve used liquid pipe sealant before and it works well. This time I found that my tube of liquid sealant had dried out! I had plenty of Teflon tape on hand and I’ve also used that with no issues in the past, so I used it here. So far so good, no drips from the SL63 diff.

 

BTW I just did a differential fluid change on my recently (well 4 months ago) acquired R129 SL500. Yes I know, different forum, but some of the comments about the non-AMG R231 SL diffs makes me think that MB has been using some carryover parts. Specifically, the fill and drain plugs were internal 14mm hex and the specified oil was 85W90, which is incidentally no longer carried by MB dealers. I ordered and installed new plugs because the existing ones were heavily rusted, and I used Liqui Moly 85W90 hypoid gear oil.

Here I am removing the old drain plug. Both old plugs were rusted in place and I had to apply PB Blaster penetrant and let sit for days. Also the rust initially wouldn’t let me insert my 14mm hex key so I had to wire brush them extensively; the penetrant helped here also.



The oil that I used, and one of the new plugs from MB. Relative to the previous discussion, these new ones had a thread sealant already applied, so I didn’t add anything else.

 

Great discussion! By the way, I have found that WD-40 makes a Specialist Penetrant penetrating oil in their Blu Torch series that seems to work better than PB Blaster or even the homemade mix of acetone and tranny fluid.

 

Did you get the drain and fill plugs from MB, or are they one of the standard sizes? And how much? I'm having a hard time finding the right ones searching on-line.

 

Yep - MB. Part number 000-997-62-32, all of $2.67 each from importpartsdirect.com, who are basically Isringhausen MB of Springfield IL. I use them for all my OE MB and Porsche parts. No connection other than being a satisfied customer!

Who says dealer parts are always expensive!

 

I should add, you need to consult a good Electronic Parts Catalog (EPC) to find these part numbers. I use https://www.ilcats.ru/mercedes/?func...=1&language=en

Be aware that the .ru domain is Russia, so it’s good to be wary, but so far I haven’t caught anything dreadful or had my bank balance emptied after browsing it!

Of course given current events, you may be philosophically opposed to consulting a Russian reference site, even for our German cars…