Am I correct in that GTUs uses standard GL5 80w90 oil like the open differentials? No LSD additive? Searching gives mixed results as the GTUs differential is unique. I drained the gear oil when I changed the front dif mount and axle seals, and would like to put the correct oil in.

Thanks

 

I don't remember the weight but no LSD additive is needed.

 

I have a GTUs LSD in my S5 GXL and have had no issues with Royal Purple 75w-90 Gear Oil. I had drained the differential when I purchased it and never added any LSD additive. I've put more than 40k miles on it with no issues.

 

Short answer: Yes

Long answer: Most differential gear oil already has LSD modifiers so that it will work in all differentials, including clutch-type LSDs that need the modifier. Those who don't like to do anything the easy way can fine-tune their clutch-type LSD by using special non-LSD gear oil and then gradually increasing the amount of LSD modifier additive until the chatter disappears. Series 4 RX-7s have a clutch-type LSD that needs the LSD modifier, but Series 5 RX-7s such as your GTUs have a viscous LSD that does not need the LSD modifier.

 

Thanks for clearing things up!

 

Coming from the land of Miatas, viscous LSDs do not need anything added to the fluid. Also, the weight you're asking about is correct for these cars according to the research I've done.

May I suggest trying Motul oil? I ran it on my Miata time attack car and it never let me down.