Selous
Thanks for sharing the results of the efforts that you have put into this today, much appreciated.
It's interesting that the Redline Web site in the USA do specifiy 75W-85, however I take Redline Australia's point re the elevated temperatures here in Australia. I would have thought that parts of the US get quite hot as well, but probably not to the same extent as Australia.
I wonder what oil the JGC's have in them for a factory fill? I suspect the 75W-85, but we will never know.
I still believe that a quality 75W-85, combined with the "too frequent" diff oil changes that are specified by Jeep Aust would be OK for for normal use. Let's face it, most of these vehicles will never see off road and are really glorified shopping trolleys.
However if you do a bit of towing or plan on long road trips in the middle of Summer, then I think that 75W-90 is the way to go. Incidently, 75W-90 is not just 12.5% thicker as some people might think, it's actually about 50% thicker. A point to note thate these diffs have aluminium casings (with cooling fins from memory), and are not the old steel casings of yester-year. That will likely also help to reduce heat buildup.
So for me, as I do some towing from time to time, will probably go with 75W-90 next diff oil change. I'm just not comfortable with putting in oil that is too thick in these diffs if they have been engineered for 75W-85. I want to be sure that the oil is getting into those bearings very quickly when cold. (The "W" or winter viscosity of oils varies significantly when the "Warm" viscosity is altered, even if the 75W is the same).
In some ways, this conversation is redundant for most because a lot of original owners will likely change vehicles either near the end of warranty or 3 to 4 years when their lease or finance is up, and the reality is that no matter which oil of those discussed up the page is used, the vehicle should get to the expiration of warranty.
However there are those of us that keep their vehicles longer. We usually change our vehicles about every 8 to 10 years, depending on how well it is aging mechanically, so we like to get these sort of details right.
I do agree with Redline Aust re the engine 5W-30, and if I can get a low ash 5W-40 (by low ash I mean 0.6% by weight, not 0.8% as some so called low ash oils have, don't want to have to pay to replace that DPF anytime soon!!) that meets all other specs, then when the vehicle is out of warranty, I also will move to that. After the vehicle is out of warranty I will also be happy to ignore the Chrysler MS-11106 spec.