[Muddy]

I know GL-5 is the required oil, but what damage can be expected from running GL-4?

 

[BAC5.2]

Complete destruction of the front differential, sometimes within miles.

 

[The Rookie]

Not to mention that the synchro's (material, finish and angle) are deigned to work with GL5, use of GL4 will adveresly affect synchro perormance.

Simon

 

[steamloco76]

I did a lot of reading - here on this forum- in the Subaru owners manual- and at oil manufacturers sites- before changing the gear oil in my '09 Foz.

The conclusion of everybody in the know- including Subaru- GL-4 will destroy the front differential.

Subaru designed the entire transaxle unit to work with the high pressure GL-5 gear oil and that is the only sane choice.

FYI- I used Valvoline Durablend semi synthetic in mine which is spec'd GL-4, GL-5, MT-1 along with the military, Mack and Ford specs . Made a measurable difference in shift feel-easier and smoother. Many on these board favor more exotic brands and blends- just try and stay away from oils with a large amount of friction modifiers designed to reduce chatter in limited slip differentials. The modifiers may make the synchronizers in the transmission less effective.

 

[Muddy]

I had my car in a shop to fix a seized synchro and at the end of the whole ordeal (long story in itself) I found they put in GL-4. It was the end of the day, and I that time I'll be honest I didn't remember if I needed GL-4 or GL-5 so I drove home (about 10Km). I'm in the middle of dealing with the shop about this now so I was just wondering what the consequences would be.