Yes it requires gl-5, No they don't all have a friction modifier.. at least they don't all have FM's that are bad for MT. Some are designed for good synchro operation. However the EP additives can cause shift quality to be worse than gl-4.
That's why its not recommended to use gl-5 if the
application doesnt call for it.
I had bad luck with subaru extra S in my 2011 forester worst shift quality out of 5 or so options I tried.
The 2015 spec's subaru extra MT which is a 75w80 gl-5 gear oil. Subaru does state you can use a 75w-90 gl-5, but it may have worse shifting and fuel economy.
link to subaru "extra mt" gear oil spec'ed for 2014+ forester mt
http://parts.subaru.com/p/Gear-Oil-Extra-MT-75W80/49506107/SOA748V0100.html
Quote:
Genuine Subaru Gear Oil Extra MT 75W-80 is uniquely formulated for Subaru manual transmissions. This low viscosity fluid reduces mixing resistance, enables efficient power transfer from engine to tires and provides improved fuel economy. It has greater oxidation stability, extended anti-wear performance and is original equipment filled at the factory.
• Maximizes the performance of the Subaru manual transmission
• Low viscosity for improved fuel efficiency
Something is working 600miles on the 2015 and its already at 29.5mpg average 32+ on highway.. and that's not really driving for economy.. 75 on highway etc.
the 2011 forester topped out at about 31 max with the factory tires more like 28.5 with the kumho 4x.
Originally Posted By: Johnny248
Does it call for GL-5 in the trans? Pretty much every manual I've seen wants a GL-3 or GL-5 if it's not some sort of proprietary fluid or an ATF fluid.
That being said, doesn't basically all GL-5 oils have friction modifier? I always recall reading that GL-5 fluids are not ideal for manual transmissions. Unless it actually calls for a 75w90 GL-5 oil, I wouldn't feel comfortable running the M1 in my trans if it was something that I planned on owning for awhile.
Just my thoughts.
On a side note, I've used a bunch of different manual trans oils over the years and had the best results in with the BG Synchro Shift II fluid. Smoother results in the different vehciles I've owned than the Redline MTL. These are 75w80 applications though. I did have one car than worked very well with the MT90, and one that the Amsoil manual trans 75w90 was better in.