2014-2020 Lexus IS AWD Diff/Transfer case fluid type

LexusGuy97 · Nov 17, 2022

Hi everyone,

I have a 2016 IS awd that I will be doing a drain and fill of the rear diff and front transfer case/diff on. My owner's manual specifies the use of toyota's own 75w85LT fluid -which I have been successful in sourcing and is not cheap (although I am fine with this as I do want toyota fluid). However, the issue is the front transfercase/diff is specified at 80w90, SAE90, or SAE80W. My local dealers do not carry any of these from Toyota and instead have told me it is safe to use the 75w85LT in the front. They said they do this on customer cars without issues.

I am picky and I do not wish to damage my drivetrain components. It has been recommended to me, to purchase Ravenol's products since they carry the oil weight I am looking for (80W90). Another lexus dealer near me told me to use synthetic in the rear (which the toyota fluid is), and not synthetic, but rather mineral in the front (which ravenol oil can be).

So my questions are:
1. Will using 75w85LT in the front of my IS be safe instead of the recommended-by-the-manual 80w90?
2. one dealer said i shouldn't use syntehtic in the front. I read that this is not important in the lexus open diff - is there any risk to using synthetic fluid in the front?

Thanks for your help

Snagglefoot · Nov 17, 2022

Just happened on this. Chevrolet 4x4 trucks give pretty much the same advice, but I’m pretty sure in the case of Chevy they are just trying to save us a few bucks as the front diff is not used as much in part time 4 wheel drives. 80w90 is normally a mineral oil and if you really want to go that way, Pennzoil makes a 80w90 and so do many others. I don’t think it’s any better than synthetic but is easy to find. Sleep well.

dnewton3 · Nov 17, 2022

LexusGuy97 said:
So my questions are:
1. Will using 75w85LT in the front of my IS be safe instead of the recommended-by-the-manual 80w90?
2. one dealer said i shouldn't use syntehtic in the front. I read that this is not important in the lexus open diff - is there any risk to using synthetic fluid in the front?

1- yes; safe to use
2- open diffs are pretty much immune to fluid selection as long as the API rating is correct (such as GL-5, etc)

simple_gifts · Nov 17, 2022

dnewton3 said:
immune

maybe "indifferent" is a better word?

JeffKeryk · Nov 17, 2022

I used Red Line 75w85 in our GS350 rear. I bought a cheap garden sprayer to squirt it in. Tight fit.

GSCJR · Nov 17, 2022

My Toyotas have only ever run on conventional QS 80w-90 GL-5, in the all my diffs and t/cases for the last 13 years. As a matter of fact, I use that in everything where GL-5 is recommended; with LSDs or not.

Greasymechtech · Nov 17, 2022

Nothing special about the LT 75w-85 and I wouldn't even bother with it

I'd run a 75w90 full synthetic in both the front and rear diff, preferably non-LS since no need for LS additives.