Rear diff oil turns dark grey

[Corniit]

Hi,

I’ve got 2016 VW 4 motion which I’ve noticed that past two rear diff oil changes the oil color turned dark grey. When I got the car, it was four years old and changed the rear diff oil it had 108k km / 67k mi and the oil looked normal. Second oil change was also after four years but 53k km / 33k mi. This was also the first time I noticed it was grey. Today after 14 months and 19k km / 12k mi, it was dark grey, similar to previous change. I’m very nervous as I’m afraid this is due to wear. I took sample of the oil and moved magnet in there, then wiped the magnet on tissue but I couldn’t see any metal shavings or shiny things there.

When I first got the grey oil, I thought that the gear oil I used wasn’t slippery enough eg. meant for Hypoid gears GL5 class oil. However, the oil was from lube advisor and rated GL4 / GL5, so it had also that GL5 mentioned. Previous oil did specifically have VAG G052145S2 -approval which from other specifications mention it to be GL5 oil (no GL4 mentioned at all). Now I added Red Line GL5+ gear oil which should have superior lubing compared to the previous ones.

Attached is pictures of the 19k km / 14 month old oil. When new, oil was yellowish in color.

My question is, do you think that the first change I did wasn’t slippery enough oil which resulted in wear of the diff gears, even though it had GL5 mentioned? And when it started wearing, second change didn’t stop it from wearing even when more slippery oil was introduced? Or could it be that this is due to clogged breather so water contamination? Or something else?

Thank you

 

[JavierH19]

Looks like the differential is defective and is failing slowly. Many diffs like the 341k mile one in my truck are still good and haven't been maintained as well. I highly doubt the oil was bad unless it was like mannol or something equally untrustworthy and lied about being suitable.

 

[FowVay]

What fluid are you using? I think those use a Haldex system which means there's a multi-plate clutch. If you're using the wrong juice you're going to have issues with clutch wear.

 

[Tkonrr]

The front differential fluid in my 2015 Jeep Wrangler drained out like grey paint a couple of years ago. I checked on the fresh fluid I put in the differential a few weeks later and it was a clear amber appearance, not gray. I replaced it again about a year ago and it drained out a light amber, not gray at all. I believe a bit of water got into the differential somehow. The fill and drain bolts were closed tightly and the vent hose was attached firmly on the nipple on top of the differential leading up into the upper part of the engine bay just fine. I'd replace the fluid and check its condition in a few weeks.

 

[edyvw]

Hi,

I’ve got 2016 VW 4 motion which I’ve noticed that past two rear diff oil changes the oil color turned dark grey. When I got the car, it was four years old and changed the rear diff oil it had 108k km / 67k mi and the oil looked normal. Second oil change was also after four years but 53k km / 33k mi. This was also the first time I noticed it was grey. Today after 14 months and 19k km / 12k mi, it was dark grey, similar to previous change. I’m very nervous as I’m afraid this is due to wear. I took sample of the oil and moved magnet in there, then wiped the magnet on tissue but I couldn’t see any metal shavings or shiny things there.

When I first got the grey oil, I thought that the gear oil I used wasn’t slippery enough eg. meant for Hypoid gears GL5 class oil. However, the oil was from lube advisor and rated GL4 / GL5, so it had also that GL5 mentioned. Previous oil did specifically have VAG G052145S2 -approval which from other specifications mention it to be GL5 oil (no GL4 mentioned at all). Now I added Red Line GL5+ gear oil which should have superior lubing compared to the previous ones.

Attached is pictures of the 19k km / 14 month old oil. When new, oil was yellowish in color.

My question is, do you think that the first change I did wasn’t slippery enough oil which resulted in wear of the diff gears, even though it had GL5 mentioned? And when it started wearing, second change didn’t stop it from wearing even when more slippery oil was introduced? Or could it be that this is due to clogged breather so water contamination? Or something else?

Thank you

View attachment 291621

View attachment 291622

OK, VERY IMPORTANT question here:
Did you change fluid in rear differential or Haldex unit that is located just in front of rear differential???

 

[Corniit]

OK, VERY IMPORTANT question here:
Did you change fluid in rear differential or Haldex unit that is located just in front of rear differential???

Oh no.. I'm not stupid. I know the differences between the diff and haldex fluids. I do change the haldex fluids more often and clean the filter (gen 5).

 

[edyvw]

Oh no.. I'm not stupid. I know the differences between the diff and haldex fluids. I do change the haldex fluids more often and clean the filter (gen 5).

OK, just making sure we are on the sam page as you know they are close to each other and Haldex plug is more visible, so mistakes are not excluded.
Why don't you go with OE fluid and see what happens?

 

[Corniit]

For next change maybe I’ll try the OE oil. Most likely it’s the same stuff that I used previously..

Breather is not accessible as far as I know without dropping the diff so would it be good way to test its functionality if I machine hose adapter to the fill hole threads and carefully try to build pressure with Mityvac and see whether it vents without pressure build up? Should there be one way valve as well so if I check also vacuum, it should make vacuum as well?

Other thing regarding that oil sample I took. Is there a way of testing it at home to overrule water contamination or metal wear? For water contamination, if I heat it to 100°C / 212°F and wait for a while for the possible water to evaporate. Would it then clear up if it was water which turned the color to dark grey?

Or, leaving it still for days / weeks, if the grey matter settles on bottom and top is clear is it then clear that it’s wear metal?