Very satisflied with Red Line LSD fluid.

However I still wonder what is the difference between viscosity 75W-90 of Red Line and SAE 90 that the workshop manual recommends for Limited Slip Differential ?

 

They are the same thing - 90 weight is the operating temperature rating for SAE90 and a 75W90.

The only difference is that a 75W90 is not quite as outrageously thick when cold (but still thicker than when at operating temp).

Since Redline uses "Ester" (Group V) oils as there base - they naturally have a wide temperature range and generally require little to no Viscosity Index Improvers (VIIs) to achieve the 90 weight at operating temp while being better flowing when at room temp (75W), which is good as VIIs can shear over time causing the oil to thin out and the base oil cannot.

RL is a superb product, amongst the top 3 or 4 oils you can buy, use with confidence.

 

your knowledge of these lubricants seems pretty comprehensive - crossing brand names. i am very impressed.

 

I put the Redline LSD fluid in my diff a few thousand miles ago, and all is well.

 

Thanks! It has become quite a hobby of mine and something I enjoy researching and learning about. Hopefully the info I share provides at least one perspective to consider.