Hello,

I was wondering if anyone has tried synthetic differential fluid such as Mobil 1. My car is a 300 SD.

If so, does anyone know what is the proper viscosity?

Thanks,
mbz owner
84 300SD 235K
83 300SD 130K

Last year when I changed the differential fluid in my '83 300CD-T, I used Red Line (synthetic). I've used several of their other products so I was already fairly convinced of the quality of their products.

Without looking at the bottle, I don't recall the viscosity. Nice part was I called them and told them what the owner's manual said and then I got passed to a fellow who seemed to be an expert in these lubrication matters. He asked me the model and year and told me what to use. So far, I've been pleased with the results (I suppose I'd only have a negative opinion if something bad ensued subsequent to the new fluid being put in). For now, the rear end seems to function as I'd expect.

Two other things:
It is an excellent idea to clean the vent on top of the differential while you're in there. Also, make certain that the fill plug will unscrew before you go draining out the old fluid...

Good luck-

I run Redline 75W90 in both of my cars' differentials.. I'm confident that, especially in the differential, synthetic's the way to go. And definitely clean the vent properly while you're in there!

Best of luck, Michael
'92 500E
'88 300TE

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Thanks for the advice...


Has anyone tried the Mobil 1 synthetic diff?
What grade would you use in an 84 300SD?