75W-90 OK for Differential?

[xvvvz]

I looked up in the MB WIS and it recommends SAE 85W-90 or 90 for the rear differential. I can't find either in the Atlanta area. What risk am I taking by going with Mobil 1 75W-90 synthetic on my 99 230 Kompressor engine? I did a search and see some posts say 75w-140 (I can obtain that too), others say MB fluid only or you are going to hell, others say 75W-90 is fine. The car only has 33k on it but after 9 years I think it is time to change it just for insurance.

Won't 75W-90 just be a bit more thin with equal protection at cold temps compared to 85W-90 but then provide equal protection once things warm up?

Thanks for any insights and assurances you can give me. I would rather not patronize the stealership at their rip-off prices if not necessary.

Thanks in advance!

[c280nz]

i run 80-90 in my diff, so yea if the only option had been 75-90 when i purchased the oil i would have got that no worrys,
it wont be the oil that lets ur diff down anyway itl be those shit plastic bushes on the spider gears :(

[allirroz]

Originally posted by xvvvz
. What risk am I taking by going with Mobil 1 75W-90 synthetic on my 99 230 Kompressor engine? I did a search and see some posts say 75w-140
Thanks in advance!

What I've learn though and I could be totally wrong on this one, but this was the suggestion of my mechanic and he in my opinion is no slouch.
(he knows his stuff) He built a 1000 hp Porsche 911 for Autothority and was magazine featured.

That switching to synthetic is not always better. The rear diff does not specify synthetic in the book . Synthetic although better is thinner and could cause whining down the road because originally our cars were pre loaded from the factory with regular diff fluid only.

I did mine a few weeks ago and used Lucas 80-90W reg fluid.

[jnenad16]

syn 75w-90 is fine, it wont whine or cause premature wear, infact, expect a pleasant MPG increase. I would highly recommend you add one lubegard gear oil treatment, you wont be disappointed.

nenad