BMW Differential Fluid Applications
This answer is applicable for many BMWs in addition to the one listed below.
car year: 2004
car model: X5 4.4i
I want to replace the gear oil in both the front and rear differentials. Your on-catalog lists 75w-90 and 75w-140NS (both synthetic). I am pretty sure X5′s do not have LS differentials, is that true? Which weight oil do you suggest? P.S. I do pull a 5000 lbs. travel trailer periodically, live in Albuquerque, NM, and the vehicle has 86,000 miles on it.
You can use the LS (limited slip) fluid in a non-LS differential. This makes the LS rated fluids more universal in application. You would not use a non-LS rated fluid in a limited slip differential. The LS rated fluids have modifiers that allow the clutch packs in a clutch-type limited slip differential to slip when cornering … as opposed to chattering.
Both the 75w-90 and the 75w-140 can be applicable to all BMWs. Some BMWs have been originally specified for the 75w-90, some for the 75w-140. The lighter 75w-90 is the more common weight for most vehicles in the US.
BMW applications will typically specify the differential fluids as;
* SAF-XO (75w-90)
* SAFX-LS (75w-90 Limited Slip)
* SAF-XJ (75w-140)
These days, there is no real need for the heavier fluids, as long as we are using a quality synthetic, for our regular road going BMWs. The 75w-90 weight would be just fine for towing with your X5 (The X5 is specified for SAF-XO). Of course, there would be no harm in using the 75w-140, other than a slight potential drop in fuel economy.
Red Line 75w-90 (LS):