UpperDeck

A few weeks ago I changed the rear differential fluid on my 2015 3.0TFSI D4 A8 with the rear differential fluid of my S6. The C8 S6 fluid part# is G 055 190 A2. It says "Gear oil" on the bottle. I've researched for a long time, this fluid might be SAE 75W-85.

It dawned on me today that I might be using the wrong rear differential fluid since the front differential fluid of my A8 is "Axle oil" (Part#: G 052 145 S2, SAE 75W-90).

I've driven my A8 thousands of miles since the oil change and haven't noticed a problem. Do I need to change my A8's rear differential fluid immediately? Are there any potential mechanical failures from using the wrong fluid?

Any reply will be appreciated.

KnappAttack

Gear oil is gear oil. It will be totally fine. There may be a gear oil out there that will have a friction modifier in it for posi-traction rear ends but it's rare, infact I don't even know that you can get it anymore with friction modifier already in it. Audi's don't run posi-traction carriers in them. I suppose the sport differential could require a modifier in it with the clutches/brakes in there, but the sport differential is rare in a A8, specially one equipped with only the 3.0 in it. Drive on and don't worry.

Striker2237

The sport diff has two fluids in it, one for the gears and one for the computer controlled clutches. The latter is very different

UpperDeck

Do you have any idea that which one G 055 190 A2 is used for?

Thnak you.

Striker2237

Use a 75w-85 synth gear oil if that is the spec you want, I used 75w-90 in my cars for the diff sections.

MP4.2+6.0

Let your fingers do the walking. Type the part # into Google (no spaces) and look at the VW and Audi listings, especially the cross fitments. From that you can figure out what it works with and which of the units (front diff, Torsen, rear diff) it might work with and also the kind of vehicles involved--conventional logitudinal set up Torsen vs. Haldex/pretend quattro in particular.

UpperDeck

Before I made this post I spent a lot of time on Google to find out the differences between these two liquids. Unfortunately, there is so little information about these two liquids. I'm not even completely sure if the 190A2 spec is SAE 75W-85.