I've got Red Line 75/90 NS gear oil in my Sube's gear box and Mobil 1 gear oil in the diff. Been there for about 25k miles.

Since synthetic oils should have a longer useful life than petroleum oils, what's the maximum useful life for the Red Line and Mobil 1 gear oils?

I've got Red Line 75/90 NS gear oil in my Sube's gear box and Mobil 1 gear oil in the diff. Been there for about 25k miles.

Since synthetic oils should have a longer useful life than petroleum oils, what's the maximum useful life for the Red Line and Mobil 1 gear oils?

Not that I would recommend that, but I once went 100K miles on the Redline 75/90NS in my '91 Legacy. Installed Lucas gearoil and the transmission started crunching almost every gear changed. Replaced the Lucas with Redline NS again and all was smooth again. Lesson learned.

Depends very much on the way you use the car. Best case would be 60K miles/5 years, in my own humble and unsubstantiated opinion

 

 

I run Valvoline Synpower for 25-30K miles, but the car sees plenty of action on tracks.

 

Redline is also a very good oil, but Valvoline has an uncanny ability to cure the gear crunch in even 20 year old Subarus. Never had a Sube reject Synpower

hey Setright, i took your advice about changing gear oils to synpower in the transmission from searching the threads and i am so very impressed. my 98 legacy has 170k on it and the gear box feels brand new again. no hard shifting between gears or forcing shifts. im so stoked!

I use all Valvoline fluids: MaxLife Synthetic 5-30 in the motor, Synpower gear oil in the diffs, and MaxLife Synthetic ATF in the transmission and power steering. They make a good product

afterbang, thanks for reporting back.

 

 

 

And Lucid for seconding

 

 

Valvoline are really on a roll. I hope they keep making that gear oil!!