I was getting ready to change my differential fluid and, as always, I can never seem to remember which oil to use, so I came here to do a quick search.

There are the typical discussions of the best brand (Neo, Redline, Royal Purple, etc.), but most everyone seems to be using a 75w90 weight oil.

Figuring that I might be well advised to take another look at the shop manual, it has the recommendations as follows:

API Service GL-4 or 5
Above -18°C (0°F): SAE 90
Below -18°C (0°F): SAE 80

So my question: Is anyone using a single weight gear oil in their differential or is 75w90 the way to go?

Thanks!

 

I've been using Mobile 1 75-W90 for the past 12 years.

 

I believe 75w-90 is the way to go.

Get the highest performance synthetic "gear" oil with GL-5 or better for the diff since there is no brass and you want the maximum EP performance for that hypoid gearset.

David

 

Thanks for the replies!

At this point I will go with a multi-weight. I have it narrowed down to 3:
- Redline 75w90 Gear Oil
- Royal Purple 75w90 MaxGear
- Amsoil Severe Gear 75w90

 

Its funny that when I first got an RX-7 I only used Redline for the diff for awhile, then I started using Royal Purple for awhile , and now I use Amsoil. (In that order, no other oils).

 

Did you notice any difference upon each switch? Do you recommend the Amsoil over the others?