Differential Fluid Differences

[A4Qwattro]

Apropos of nothing. Why are there multiple part numbers for the rear diff fluid and what is the difference between the fluids?

KBU: G052145S2
MFS/KRR: G055190A2

KBU looks like diff code for pre-facelift auto cars (43:13 ratio)
KRR looks like diff code for facelift auto cars (43:13 ratio)
MFS looks like the diff for manual cars (48:13 ratio)

Are the fluids the same? Did Audi just make a load of paperwork for somebody? Side note, the G055190A2 is also listed for the V6 cars (S4).

[Smac770]

Seems to be is the diff produced by VW Kessel or ZF.

The ZF diffs (front diff in 0B6 and 0BK, rear standard diff 0BD) use G 052 145 S2.
https://www.toolsinfoweb.co.uk/conte...tic%20gear.PDF

The VW diffs (front diff in 0AW CVT, rear standard diff 0BC and sport diff 0BF) use G 055 190 A2, which has replaced G 052 190 A2 in recent years
https://www.toolsinfoweb.co.uk/conte...iable%20au.PDF

The 190 gear oil seems to be GL-5 75w-85, while the 145 gear oil is unclear as to if it's GL-5 75w-85 or GL-5 75w90.
You can see from the SDS documents they are not exactly the same hazardous components content.

G 055 145 A2 is the gear oil for the Torsen center diff in the ZF transmissions.
G 052 145 A1 was a 0.5L bottle that got dropped some 8 years ago leaving just the S2 1.0L bottle.
G 052 145 A2 is something different that hasn't been around since the start of the century.

None of this applies to the 6MT or DCT transmissions as the front and center diffs are in a common oil chamber with the gearbox MTF.

[A4Qwattro]

Legend. Thank you. The MSDS also shows the oil properties. The 145 oil seems slightly thicker than the 190 oil at 100C but a lot thicker than the 190 oil at 40C. In general, the 145 oil is thicker than the 190. I wonder why that is:

Kin. Viscosity (at 40C)
G052145: 116.5 mm2/s
G055190: 69.6 mm2/s

Kin. Viscosity (at 100C)
G052145: 17.0 mm2/s
G055190: 11.4 mm2/s

Knowing Audi, they must have done it to reduce fuel consumption.

According to this conversion table https://petroleumservicecompany.com/...scosity-chart/ (Kin viscosity, to SAE Gear) which I'm not sure that I know how to read, the 145 seems like an 85w-90 oil. The 190 oil seems like a 80w-85 oil. So it seems like the oil update was just to thin it out to reduce fuel consumption...unless there are different additives.

[Smac770]

VW going thin for the fuel economy is a safe assumption. ZF making their own stuff with a bit more robustness. Which I find curious since the ZF made 0BD rear diff is only for the ZF transmissions with the 2.0T, and has a lower torque rating than the 0BC. It might also have to do with the gear teeth or the axial offset or other such engineering differences. That was something Audi pointed out for the DL382 second gen DCT: "The short pinion shaft runs at right angles to the crown wheel, and there is no axial offset. This permits the use of low friction spiral teeth and low-viscosity MTF (gear oil) in the bevel gear." That being in a DCT where the front diff uses the gearbox MTF.

[A4Qwattro]

Apropos of nothing again. The ZF and VW Kessel rear diffs have different drain plugs apparently...This is neglected in the parts catalogs of the mainstream vendors like FCP Euro and ECS Tuning.

The ZF diff (KBU) has an M16x1 fill plug. The VW diff (KRR/MFS) supposedly has the M22x1.5 thread just like the 0B2 6 speed box. This is nice since you can get the magnetic drain plugs in that size for the diff. Regrettably, the nuts at VW spec'd an aluminum fill/drain plug for this box. Part number is N10037105 (KRR/MFS diff codes). Maybe for weight and cost savings if they assume the diff would never be opened. Aluminum plugs is a great way to end up with a stripped/stuck fill plug.

If you wanted steel plugs, you might try the M22x1.5 from the 0B4 6 speed which is M22x1.5 (N10037106) or the M22x1.5 plug from the 0B2 6 speed (WHT005804). No idea why they have so many part numbers for the same thing. The 0B2/0B4 also has an aluminum casing so not a big deal to have dissimilar metals threaded together.

[Chillaxin]

Info I collected here: https://www.audizine.com/forum/showt...1#post15001916

All are 75W-90

Amsoil Severe Gear GL5 Viscosity@40C 97.8 cSt, Viscosity@100C 16.0 cSt, Pour Point -43C, Flash Point 222C

Amsoil Long Life Gear GL5 Viscosity@40C 115.8 cSt, Viscosity@100C 15.7 cSt, Pour Point -48C, Flash Point 208C

Liquid Moly Hypoid Gear Oil GL4/5 Viscosity@40C 106.0 cSt, Viscosity@100C 15.6 cSt, Pour Point -50C, Flash Point 200C

Liquid Moly HP Gear Oil GL4+ Viscosity@40C 81.5 cSt, Viscosity@100C 14.3 cSt, Pour Point -60C, Flash Point 200C

Redline GL-5 Gear Oil Viscosity@40C 108 cSt, Viscosity@100C 16.1 cSt, Pour Point -45C, Flash Point Not Listed

Redline MT-90 GL4 Viscosity@40C 82 cSt, Viscosity@100C 15.5 cSt, Pour Point -45C, Flash Point Not Listed - This is what redline's website recommends for F/R Diffs for B8 A4 with ZF8speed.

After looking through all of these, the best oil for fuel economy would be the LM GL4+ available from FCP. The automatic doesn't produce high shock loads or extreme pressures of a non-tracked car mostly used for commutes. This benefit would be amplified in cold weather and short trips. If I were to track or race, or had a manual that did launches, that would be a different story.

I just did some digging around and thought I'd share this info for anyone looking.

[Allroad Offroad]

Owner of europe DSG 7 speed allroad, I had my mechatronic serviced along with new oem clutch packs and car is sitting on 215k km with the new cdnc 2.0tfsi engine replaced at 180k km. I want to replace my rear diff oil (KLL code) and on 7sap it says G055190A2 oil to be used.

As an alternative I found FEBI 48785 GL-5 75w85 (SAE J306 class states it as a 75w80?) (40C 78cSt and 100C 12cSt) oil standards. Can anyone confirm if this would be suitable for my case? I don't care about the efficiency and far as I know gl-4 standard is not suffice for most hypoid gear diffs due to shock loads but again I'm not experienced with Vag designs and specs.

[A4Qwattro]

edit: typo, see below.

[Smac770]

KLL uses G055190A2. If you search for that on Febi's website, it comes back with 48785. They are both GL-5 75w85.

https://www.toolsinfoweb.co.uk/conte...AXLE%20OIL.PDF

Density : 0,856 g/cm3 at 15 °C
Viscosity, kinematic : 76,14 mm2/s at 40 °C
Viscosity, kinematic : 12,27 mm2/s at 100 °C

https://cdn.partsfinder.bilsteingrou...LP48785_GB.PDF

Density [g/cm³] 0,85 (DIN 51757) (15 °C / 59,0 °F)
Kinematic viscosity 78 mm²/s 40°C (DIN 51562)
@100C not stated