Apples and oranges man, you are confusing differential gear oil with motor oil. The differential oil for the VX comes in pretty much two flavors: 75W90 and 75W140. They are different from normal motor oils. The are thicker and smell funky. I personally used the Mobil1 75W140 full synthetic and it was pricey ($18 a bottle I think) as hell. You can use an off brand non synthetic for far less, but personally I didn't want to chance it. You may also want pump for this stuff as it can sometimes be a PITA to fill the differential, although you can just try and use the bottle. I looked at the temperature ranges listed on the sides of both types of bottles and really couldn't find a compelling reason to use the 75W90 at all. The 140 is good across a far broader range and where I live the temps like to stay on the higher side, and then dip really low at night. If you are going to service the rear at the same time as the front don't forget to get a tube or bottle of limited slip differential additive(LSD) for the rear differential only.It states that 75W90 is the equal to regular 10W40????????????