Z3 2.8 Rear Differential fluid

Hi All,

I own a 1998 2.8 Z3 and it's time to change the rear diff fluid. According to my workshop manual I should be using SAF-XO oil 75W90. I have spoken to a few dealers and they assure me that i should be using part number 83-22-9-415-961. Based on my research is a 75W140,or SAF-XJ used in an LSD Diff. Unfortunately, I have the open Diff, and as such believe that it should be part number 83-22-9-415-960 which is supposed to be the SAF-XO.
As the dealers buy their oil in bulk, they have been unknowledgeable about the oil's type. Can a Subject Matter Expert please shed some light. And provide the correct BMW part number.

Thanks,

The open diffs and the Torsen limited-slip diffs get SAF-XO per the BMW TIS. The clutch-type limited-slip in the M cars gets SAF-XJ.

That being said, I used Amsoil Severe Gear 75W-110.

Diff fluid specifications got an overhaul a few years ago and 75W-110 was introduced. The upper viscosity range was extremely wide for 75W-90 so they narrowed that spec down. 75W-110 now fits in what USED to be the upper viscosity range for 75W-90 and is what a lot of people are using in their Torsen limited-slip diffs. 75W-90 is still spec'd for the open diffs.

However, are you sure that it's an open diff and not a Torsen diff? Go to http://www.rubmw.ru/vincode/eng/ and enter the last 7 characters of your VIN. If it says "differential lock 25%" for your final drive, you've got a Torsen diff and I would recommend the 75W-110. The only down side to using 75W-140 is a little reduced efficiency and reduced cooling of the fluid. Nothing catastrophic that I'm aware of. Unfortunately I can't give you part numbers because I haven't considered using factory fluids.

Hi dkindig,

I checked the site and I don't see Differential lock anywhere. I did raise the car and spin the rear wheels while in 1st gear and they rotate in opposite directions, thus open diff, Unfortunately! So what you are saying I can use any of the oils, XO , XJ without concerns, would this be correct?

Originally Posted by rupertnagi

Hi dkindig,

I checked the site and I don't see Differential lock anywhere. I did raise the car and spin the rear wheels while in 1st gear and they rotate in opposite directions, thus open diff, Unfortunately! So what you are saying I can use any of the oils, XO , XJ without concerns, would this be correct?

Yes, although XJ will probably result in slightly lower mileage, and it won't cool as efficiently because it takes longer to return to the bottom of the diff...

I see. Better stick with the SAF-XO then. Do you know who manufactures the oils for BMW? Is it Castrol? Can i use any 75X90? The dealers tens to put a scare tactic in place enforcing that the use of any other oil will harm the Diff.

I use Mobil 1 gear lube in all my cars, except the E46 M3, which has the variable LSD, so it gets the Castrol SAF-XJ.

Originally Posted by Pinecone

I use Mobil 1 gear lube in all my cars, except the E46 M3, which has the variable LSD, so it gets the Castrol SAF-XJ.

Which Mobil 1 do you use, 75w-90 or 75w-140? I keep a supply of both on hand in the garage, because I use them in my BMW motorcycle transmissions and FDs and in the differentials of my 4x4 Jeep Liberty. I have always used the BMW gear oil in the Z3, but it would be nice to keep one less gear oil on hand.

Hi rupertnagi-- Were you able to locate the differential lock? If not, on my list it is the first item listed under the Standard Equipment section.

Hi,

I checked and it does indicate Differential lock 25%, What exactly does that mean by 25%? I did jack up the Z3 and the wheels turned in opposite directions, so i assumed that I didn't have the LSD. Does the Torsen Diff spin in diff wheels spin in opposite directions? Some clarity would help as every time I think that I have the answer another questions arrises.

Thanks,

Rupert

Originally Posted by rupertnagi

Hi,

I checked and it does indicate Differential lock 25%, What exactly does that mean by 25%? I did jack up the Z3 and the wheels turned in opposite directions, so i assumed that I didn't have the LSD. Does the Torsen Diff spin in diff wheels spin in opposite directions? Some clarity would help as every time I think that I have the answer another questions arrises.

Thanks,

Rupert

You have the Torsen LSD on your car and should use a 75W-90 or 75W-110 diff fluid with a limited-slip additive. The reason I pointed you in that direction (researching your diff) is because most of the six-cylinder cars came with a LSD. One of the reasons I use Amsoil is that the additive is in the fluid by default rather than adding it. I would highly recommend the 75W-110.

25% means that when a wheel starts slipping, 25% of the total torque applied to the diff is directed to the wheel that ISN'T slipping (hence, the term limited-slip). More info here: http://bmwtips.com/tipsntricks/tips_...fferential.htm

Does the Torsen diff require the anti-slip additive since this diff is more mechanical and doesn't have the wet clutches as other limited slip differentials?

Originally Posted by nfunk

Does the Torsen diff require the anti-slip additive since this diff is more mechanical and doesn't have the wet clutches as other limited slip differentials?

Maybe someone has better information, but I don't see why a Torsen (TORque SENsing) diff would need anti-slip additive, although it should not do any harm. Torsen diffs work via the angular interaction of the gears inside the differential, and not by any clutch plates or other sliding/slipping surfaces. My understanding is that the amount differential rotation allowed by a Torsen (e.g., 25%) is designed in by the angles of the gears inside the differential and cannot be changed without changing those gears.

I use the 75W-90 in the cars. 75W-140 in the Jeep.

IIRC, Mobil 1 has the limited slip additive in it. But you can always add some, not a huge deal.