Amsoil diff fluid

[98LSC32V]

What do you guys think, should I use the Amsoil Severe Gear 75w-90 or 75w-110 in my 98 Mark VIII which has the Ford 8.8 28 spline open differential? Basically what I want to know is will I get worse MPG with the heavier diff fluid?

 

[Steelers]

No, you will not get worse MPG with the 75w-110. Often, there's no difference in fuel economy between using a 75w-90 and a 75w140. I would think Amsoil's new 110 weight gear lubge in an older Mark VIII would be a good choice.

 

[Pablo]

I agree with Steelers - I doubt you will notice any change in practical usage. In theory, in the lab, yes but not necessarily day to day. Also, maybe precision measurements of the years might see a difference.

However, the trade off for slightly better wear is well worth it.