change your dif fluid frequently
 

background:

2018 ss 1LE. 0 track time. no dd, no winter use.

bolt ons & ethanol @ 16k miles
changed rear dif fluid @ 6, 14 & 24k miles
using factory ac delco dif fluid

the most recent fluid change took place a couple weeks ago. i didn't dump the fluid out of the container i caught it in until yesterday. it had 2 weeks to settle. i poured the oil out of the container and was left with this gom. i snapped a pic of it, then ran my finger thru it and snapped another pic.

the car has never seen a road course or autox, all street miles. rear doesn't make any noise and works fine. that is 1 calendar year's worth of stuff.

thought i would share and enter it as evidence to change the dif fluid frequently, even if the car isn't tracked. i change it every spring no matter what. might add another change in the middle of the year.

the container was new and i planned this out. never expected to find a 1/2" of metallic silt in the bottom with only 10k miles on the oil.

I found the same dark gray fluid when I changed at 1500 miles. There is another thread where someone pointed out that the black color is coming from the carbon black coating on the diff gears when they are produced (and before incorporated into the diff housing). Supposedly the black coating would come off fully after 2-3 diff fluid changes, and subsequent changes would see fluid that looks much more like fresh fluid.

Since your experience seems to differ a bit (plenty of black color in 3rd fluid change), I'd guess it might be due to how you use the car (road use only, no track). Perhaps using the diff more aggressively (twisty track with aggressive throttle) will get the rest of the black coating out of there for good.

Not sure about the metal particles though....

idk. if i had saved and added up all the blackish goo that came from dif changes id have a solid 1/2 solo cup full. the rear dif gets its workout, on track or not. i use the recommended dexron fluid. oh well. ill stick to once a year unless i start frequently putting the car on track.

That was me lol. Crown wheel and pinion gears get coated in Black iron oxide as opposed to Red iron oxide (RUST). This is very normal. After a few changes it goes away. I honestly wouldn’t worry too much about trying to get it all out you will go crazy. I have had theories that as the coating wears off, the lashing increases but I do remember changing ratios on my fox body and the gears had none or minimal coating on the teeth.

So if I changed my diff fluid at 1500 miles and then just did my first road course track day, should I now change the diff fluid again?

I did my diff fluid at 1,500 miles and the fluid looked quite OK. The magnetic plugs didn't really have much on them, either. Looked nothing like what you show in your picture, my fluid looked far more 'new'.

I'll probably do it again at 5,000 miles and then leave it for a while after that until 30K or something.

I’ll put something into perspective. I have a 300k mile explorer that has seen more abuse than any car on this page. I have never changed the diff or the bearings and it still spins. I wouldn’t get too bananas about having un-contaminated fear oil. The gears are always under pressure. Significantly more than any engine oil. There is a theory that synthetic fluids in diff actually break down faster than dinosaur oil.

If you are changing your diff fluid because you are full tilt at the track and know you are breaking down the synthetic esters then that is understandable. But there will always to some capacity be metallic particles in the oil. Obviously we don’t want to see chunks of metal but a glittery look is not abnormal.

Changed my diff oil today to RP. 2SS with 3500 miles on it.
The factory fill was clean. There was zero residue on the fill plug and only a small amount of sludge on the drain plug.
Street driving. Top down cruzing. Wife commuting. A few hard blasts just to blow the gunk out.

i change mine once a year but i did mine at 1500 miles and then yearly only at 33k now and almost 6 years