Is SAE 80-90 ok to use for rear axle?
 

I'm reading MB states the rear diff needs SAE 90..

I found a new bottle of Castrol Hypoy C Gear Oil 80-90...will be ok to use or should I go buy the correct one?
I'm not familiar at all with gear oil.

Thanks,
Robert

I use Mobil 1 synthetic 75w90 in all of mine with no issues.

What are the change intervals between Synthetic and non?

Castrol Hypoy C Gear Oil 80-90 is fine. I've had it in my differential for a few years now. I checked it just a few days ago, and it was very clean.

Ok cool. The guys at pepboys told me a while back (I do my own oil changes now though...) that they checked it and the oil was "like water"...so it needs to be changed.

Process looks straight forward. Remove fill plug, drain anything that comes out. Remove drain plug, drain all out. Replace drain plug. Fill until it starts coming out of fill plug then put fill plug back in.

Sound right? Any other tips?

Not sure about the interval, I do mine every few years....so probably 35-50k or so.....if I drove more than 14k a year I'd probably do it every other year.

I used some Valvoline Durablend 80W-90 stuff last time I changed out my diff fluids. I change out diff fluids every spring. I really don't care for how many miles the car has racked up in a year, it gets changed out every spring. Keeps my fluids fresh. Pointless, sure. Insane, maybe. :D

I used 80-w90 leftover from changing the diff oil in our Cat tractor... seems to work just fine.... This was a special one that was Cat spec though....

Very few MB differentials are limited slip, but for any car with a limited slip, go ahead and use 80W90, but get a tube of friction modifier additive and put it in first, then fill.

Differentials and manual transmissions don't deal with the by products of combustion as does engine oil, so it will always look clean. Change it about every 100,000 miles and you will be in good shape on that front.