Why 75W90?

[ant]

I have a 2004 Dodge CTD with a 11½" AAM axle with the TracRite differential, which is similar to a Torsen type design.

The owner's manual specifies 75W90 for all conditions including towing. The same axle in Chevy Duramax trucks have a Eaton differential and I think, have 75W140 gear oil.

My question is why 75W90 when 75W140 is the usual recommendation for towing conditions? Is the oil weight required for proper function of the differential? Some have said the oil weight is due to CAFE standards, but I don't think this is a factor with diesel trucks.

 

[MolaKule]

Supposedly, the other factor is that different GL viscosites give different torque biases, so a Torsen is supposedly sensitive to lube weights.

 

[ant]

Molakule:
Last summer there was a thread that you mentioned the viscosity of HDS-5 75w140 was incorrectly listed on the website. "Addendum: The figures listed were for some earlier fluids and needs updating. Our latest tests on HDS-5 75W140 show a 40 C vis of 287 cSt."

What are the latest viscosity figures for the HDS-R and HDS-5 oils?

 

[MolaKule]

We are going to be updating and making some changes on the website and specs will be one of those.