90W for Toyota and Lexus Rear Differentials?

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In some of my owner's manuals (including my son's 2009 IS350) they call for 90W in the rear differentials. 75W90 in front and transfer cases.

I'm trying be true to the owner's manual and there has to be a reason they did not specify the 75W-90 for the rear. They do give the option
of using a 80W90 if it gets below 0F.

It seems "everybody" is using a 75W90.

Remember, this is BITOG and some of us have inquisitive minds and some don't.
And you can see in my sig I have been very successful in using Amsoil and Schaeffer gear lubes.
This is a question for knowledge.

There has to be a reason they choose 90W.
 
Just another data point: Amsoil Severe Gear 75W-110 in my 4Runner's rear diff and transfer case.
 
I think I made a mistake in my question. I may be getting "SAE" and "W" confused.
 
If your driving through a cold winter I would surely put a 80W- or 75W-90 in there. Unless its 1 ton dump truck or a clutch bangin' MT drag car with 300+HP You likely don't need the shock cushion of thick goo back there. The additives do the magic.
 
Originally Posted by crainholio
Just another data point: Amsoil Severe Gear 75W-110 in my 4Runner's rear diff and transfer case.


What year is your Runner?
 
Lexus IS350 is a sedan.

Unless you are using it to tow, just get regular gear oil with 75W90 or similar viscosity.

Reason to go with thicker viscosity is towing.
 
Note that some of these sedans have differential capacities of barely over one quart.

My 2017 Lexus GS-350 calls for 75W-85; I use 75W-90.
 
I've always used 75W-90 in the Toyota diffs I've touched. Some of them call for Toyota Differential Oil LX if equipped with LSDs. Supposedly Red Line 75W-85 does work in those.
 
My Toyota Tacoma calls for 90 weight gear oil in the rear and 75w-90 in the front differential and transfer case. I've used 75w-90 in all three since changing out the factory fill. No issues with any of them. 90,000+ miles.
 
Some silly games from the OEM … GM rear calls for 75W85 and the front pumpkin 75W90 … do any grownups proof read these manuals (like I must do at work) …
 
Originally Posted by JLTD
Originally Posted by crainholio
Just another data point: Amsoil Severe Gear 75W-110 in my 4Runner's rear diff and transfer case.


What year is your Runner?


2007 with 206K miles, driven in NJ all seasons...cold Winters, hot Summers. I use the same fluid in our '09 Subaru Forester front and rear diffs, 112K miles and no complaints. If the extra viscosity is costing me fuel economy, I can't tell.
 
90 grade gear oils used to refers to KV@100C range from 13.5 to 24.0 cSt, in gear oil speak is ranging from ISO 150 to ISO 320 gear oils.
SAE 90, being monograde, falls into ISO 220-320, whilst multigrade say, 80W90 falls into ISO 150 to ISO 220 gear oils.

Post 2005, the single 90 grade were divided into 2 categories. Namely current day SAE 90 AND uncommon SAE 110.

Hence in literal translation(?), a pre-2005 monograde SAE 90 should be directly equivalent to (uncommon) current SAE 110 whose KV@40*V ranges from 220 cSt to 320 cSt.

Current day 75W90 is basically an ISO 100 gear oil with KV@40*C of 100 cSt thereabout.
 
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