Can anyone tell me the difference between the Amsoil W 7590 W 75 140 fluid 2008 LR two calls for 75-90 is it OK to use the 75 140? Is it better?

 

Seems to be a lack of understanding of oil viscosity and the importance of the 75W portion of the number and the significance of the -90 portion.
Some would pipe in (without an engineering background) and offer the wrong opinion.
In short, I would not do that to my vehicle. Your vehicle, your choice. Mileage WILL vary.

 

In this car I would generally use the OEM spec fluid (not necessarily land rover branded, that's very expensive).

Two exceptions:

Engine Oil: I've always used Mobile 1.

Rear Diff: Due to failure tendency I use AMSOIL Severe Gear Synthetic 80W-90. That's worked for 100K miles since I had to replace the original diff. My manuals say the OEM fluid is castrol EPX 80W-90 (non synthetic).

But I would stick with the correct weight for sure. In addition to wear, that can affect heating, fuel efficiency, and limited slip performance (not sure if that applies to this car).

 

Well, 75 is the low common denominator, a good thing! The upper 140 is the per say "boiling" point of the gear fluid, where it starts losing viscosity, will not hurt one bit. Might actually help. One caution with Amsoil, amazing stuff but priced it's self out of the market for me, it has a lot of detergents so if you have never used it in the diff before, don't skimp on the timing of the next gear oil change.
Another tip, the original design starved the main bearing for fluid, fill it till it leaks. It has a breather so, any pressure has an escape.
Mileage will vary.

 

Thank you for the answer on the 7590 and the 75 140 great info. I also added an additive liquid molly .LIQUI MOLY MoS2 Antifriction for Gears | 50 g | Oil additive | SKU: 2019 https://a.co/d/bWeYaHe
Trying to avoid another differential failure and didn’t think it would hurt to add it

 

I use the moly annually with the diff oil change.

 

My engine is about to pass 200,000 miles and still sounds like a well-oiled sewing machine. I credit Liqui-Moly MoS2 for that, 100%. And I just bought three tubes of the gear additive.