12' G37xS Sedan AWD

Why does the manual call out for 80w90 for the front differential fluid and the rear differential using 75w90?

Does anyone know the actual reasoning behind this? Its just a question out of curiosity more than anything else. The only logical reason I could think of is because the front diff gets heats from the engine.

 

The front diff is also not used 100% of the time like the rear, front only works when rear slips,

 

I did consider that but wouldn't that effect the all around weight as well? So maybe like a 75w85 instead?

 

Honestly, I just use M1 75w90 in both and call it a day.

 

I may be doing the very same thing. I found Mobil 1 Synthetic 75w90 and was told 80w90 is a lot more rare to find.

 

Also every time the car takes off from a stop or is at low speeds.

 

do yo u need to change both ? or just rear?

 

Both. At 35k mine were both pretty dark