75w90 or 75w140 differential fluid?

[Jon K]

I went to the speed shop and bought Royal Purple 75w90 gear oil for the rear end. I have a limited slip differential. apparently, though, the OE fluid is 75w140? What should I do?

[632 Regal]

LSD's use the thick stuff, opens use the thin stuff.

[ryan roopnarine]

take it back to the same store and ask to exchange/pay the extra for the royal purple 75w140? i have the same fluid (RP 140) and it works great even without additive.

[bfd]

I went to the speed shop and bought Royal Purple 75w90 gear oil for the rear end. I have a limited slip differential. apparently, though, the OE fluid is 75w140? What should I do?

Where is the requirement that you need to use 75w140 gear oil for your rear end?

I'm using RP 75w-90 SynMax gear oil in my 1990 535i, 5spd, 109K miles. I have a limited slip and it seems to work fine. My owner's manual states I can use any 90w gear oil. Before this last oil change, I used Redline.

If you're not happy with the 75w-90, can you exchange it?

[ryan roopnarine]

Where is the requirement that you need to use 75w140 gear oil for your rear end?

I'm using RP 75w-90 SynMax gear oil in my 1990 535i, 5spd, 109K miles. I have a limited slip and it seems to work fine. My owner's manual states I can use any 90w gear oil. Before this last oil change, I used Redline.

If you're not happy with the 75w-90, can you exchange it?

bentley (among other places) says that non LSD takes BMW SAF-XO rear end oil. LSDs take SAF-XLS. one (or either) has been superceeded, but the weights stay the same. saf-xo is a syn 75w90, saf-xls is a syn 75w140. the SAF designation is by castrol, as they make the "BMW" specified rear end oil.