Rear differential gear oil ...

[KurtM]

I was going to use Castrol Hypoy C 80W-90 gear oil.
Any opinions

Thanks
Kurt
95 525ia

[gale]

I checked Castrol's website & it meets the GL-5 spec and that alone is sufficient. If yours has the limit-slip diff, you may need to buy a 4 or 6 oz bottle of lsd friction conditioner as well to keep it from groaning during slow tight turns. Most synthetic diff gear oils are sufficient without the additive so it may be cheaper to go with synthetic gear oil. I believe the current BMW spec calls for synthetic GL-5 gear oil for all diff's. 80W90 is good for most applications, some use 75W90 or 75W140 depending on climate.

[632 Regal]

I checked Castrol's website & it meets the GL-5 spec and that alone is sufficient. If yours has the limit-slip diff, you may need to buy a 4 or 6 oz bottle of lsd friction conditioner as well to keep it from groaning during slow tight turns. Most synthetic diff gear oils are sufficient without the additive so it may be cheaper to go with synthetic gear oil. I believe the current BMW spec calls for synthetic GL-5 gear oil for all diff's. 80W90 is good for most applications, some use 75W90 or 75W140 depending on climate.