On Saturday, August 19, 2017 at 10:48:06 AM UTC-4, Bram van den Heuvel wrote:
Given ,
wrote:

Rerally nothing of you don't need synthetic. All you NEED is a simple
GL4 gear oil like the Walmart LubKing GL4. Synthetic doesn't thicken
as much in the cold, or thin as much in the heat, and MAY last a
little longer, but not enoughlonger to make it worth 4 times as much
(there isGL4 oil available for as little as about US$16 a gallon)

I was hoping to get good information like that so I thank you because all
the guys on the Toyota forum are saying to only use Amsoil or Redline but
they don't really know why.

You see this on lots of those gear head forums. Where they will
spend $$$$ for super premium products that make no sense without
even understanding why. I've been at the BMW dealer parts counter
and seen people come in to buy oil at $8 a qt, they believe you
have to use only BMW antifreeze, etc. As long as it meets the
spec recommended by the auto manufacturer, it will be fine.





I'm looking at GL4 and SAE 75W90 as those are the specs from Toyota.

My one question to you is if the synthetic doesn't thicken as much in the
cold, how does it keep the 75W and if it doesn't thin out in the heat as
much, how does it keep the 90 rating?


Isn't that what the rating is all about?
So doesn't one 75W90 act the same at cold/hot as another 75W90?

The 75 and the 90 spec the viscosity at the cold and hot ends of
the working temp range and both types have to meet it. Synthetic may
exceed it, hold that viscosity profile over a wider range, but it's not
going to be an issue for your application.