[Mainia1]

Wish there was a cleaner you could put in the diff and the DCT tranny run it on a lift for a minute or two then drain and refill with the redline I use their engine oil but what is the weight to go with can the gear oil of the same weight be used in both units?

If you change it after getting it warm there is so little left in the rear diff it is a moot point. That is more of an issue with the engine which can keep 7-10% old oil in the oil cooler, turbo oil lines, and the engine oil bores.

It is different oil, as the rear diff and transfer case take 75w-90 GL-5 oil and the front diff/gearbox combo have the same cavity and there for same oil spec for both. OEM is speced at 70w 75 GL-4. I am running 75w-85 GL-4 that Hyundai WOULD use if it was not for CAFE standard BS for thinner oil. No issues with shifting in -25 below here in Minnesota, with that thicker oil. I also put it past Redline's own R&D chemist and he said no issue, good to go with the thicker oil. Will help reduce wear. You DO NOT use Redline Dual Clutch oil in the 7 speed as it is made for a wet clutch and some dry clutch's. This is more of an ATF based fluid where the 7 speed is all gear based fluid.

 

[Mainia1]

I drained my transfer case at 34,500 and it was not black but, it was dirty brown, the oil was at least used and there was no metal flakes seen when throwing a light on the cleaned out drain bucket. I used Redline 75w-90 GL5 to refill it. I also changed my DCT/front transaxle oil and it to was dirty brown with just an ever so so so slight gray tinge to it. I would not have noticed it if I did not drain the transfer case before the DCT. Not saying it is bad, as the additives in the GL-4 Redline MT 75w-85 oil I use could be making it look that way. It also could be some metals there are the sliding engagement of the gear box gears and the front diff's helical gears. No metal glitter to be seen with a light flashed on it, or in the bottom of the bucket. The refill oil was GL-4 Redline MT 75w-85 oil, a thicker viscosity then speced by Hyundai. This would be the spec Hyundai would use and has used as their spec before CAFE stands forced them to use thinner oil then they would like to. And I will add again, zero shifting issue in Minnesota -30F/35C winters.

I also used this time to change the anti-freeze w/o a thermostat swap, as I will change that out on my 70,000 mile antifreeze dump. Just a heads up to you DYIers, my car took 45 mins to bleed out the air at idle and a good couple of throttle blips during that time. Then I noticed a small drop in the tank after doing a 10 mile slow "non boosting" hwy run to get all the air out.

 

[thearborbarber]

I did my rear diff at 35k and it was filthy black. I changed it, the DCT and Xfer case at 70K and they all came out golden brown. I used Hyundai's 70w in the DCT and some Supertech from walmart 75w90 in the other two. The DCT fill bolt was a huge pain. A long reach flexhead racheting wrench got it for me. Mania's method was plan B.

 

[Mainia1]

We know from experience with the Kona/Niro/Ioniq EV gearbox that black oil is a sign that there has been no ferrous particle filtration provided such as a magnetic drain plug. The oil is not oxidised or burnt, it's only dyed from the continual crushing of steel particles down to a fine dust. Consider adding a magnetic plug at the next service and always use the factory recommended oil unless you know what you're doing.

Hyundai installed magnet plugs to our rear diffs by default, and our front DCT/front diff drain plug. That is not a issue with petrol AWD drivetrains as far as I have seen.

 

[Kiwi]

Yeah, that's good. Meanwhile, I know now what's making our EV gear oil black. Hyundai bloody Hyundai ....

 

[Thrillhouse]

Just had my 2023 Kona N-line in for first service at 3,000 km. It's been pretty lightly used since we got it in sept.. No towing or anything.

Had to talk them into changing the diff fluids of course... "we never do it" and "not recommended until 100k".
Had them do the rear diff and transfer case because it was nearly the same price as doing just the diff. Figured it was worth it just to see.

No obvious metal that I could see, but pretty dang black. They were unhelpful in telling me if this seemed normal.
Transfer case on the left, diff on the right.

 

[phornea]

Just had my 2023 Kona N-line in for first service at 3,000 km. It's been pretty lightly used since we got it in sept.. No towing or anything.

Had to talk them into changing the diff fluids of course... "we never do it" and "not recommended until 100k".
Had them do the rear diff and transfer case because it was nearly the same price as doing just the diff. Figured it was worth it just to see.

No obvious metal that I could see, but pretty dang black. They were unhelpful in telling me if this seemed normal.
Transfer case on the left, diff on the right.

Darn, the transfer case fluid looks pretty black too. Didn't expect that based on Mainia1's experience.
I did only the rear diff at 8k and am going to do the transfer case now + rear diff (again) at 24k (along with 3rd engine oil change). Lots of fluids will be changed, hehe.