Originally Posted By: aquariuscsm
I`ve been reading alot through the recent GL5 rear differential oil posts lately. It got me wondering. My car specs an 80W90 GL5 in the rear diff. I currently have the Amsoil GL5 80W90 in it. What`s the exact difference between their GL5 offerings and which one would be THEE absolute best for my car:
Severe Gear 75W90
Severe Gear 75W110
Severe Gear 75W140
Amsoil Gear Oil 80W90 GL5 (my current fill)
First I will say the best choice would be the 75W-110. At the hot end, it's most in line with what is recommended, yet still has excellent cold flow.
The exact difference between the first three is hot viscosity.
16.7 vs 20.4 vs 25.7 cst@100°C
The additives are essentially the same top of the line Severe Gear additives.
Gear Oil White Paper
The 80W-90 AGL is a bit lighter at 14.9cst@100°C. It's better (flow, load, life) than most OTC gear oils, but it is not Amsoil's top of the line gear oil. I wouldn't worry if that's what you have in there. Maybe next change step up in viscosity.
Also, this may be helpful for viscosity comparisons:
http://www.lubrizol.com/products/automotive-gear-oil/J306.asp
