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Registered
2000 Forester L
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26 Posts
Discussion Starter #1
I know GL-5 is the required oil, but what damage can be expected from running GL-4?
 

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Premium Member
2009 Outback XT-B 5MT
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10,254 Posts
Complete destruction of the front differential, sometimes within miles.
 

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Registered
99 UK S-turbo
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8,566 Posts
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
 

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Registered
2009 Forester X 4 A/T
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305 Posts
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.
 

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Registered
2000 Forester L
Joined
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26 Posts
Discussion Starter #5
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.
 
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