I want to change the gear + diff oil in my MY94 STi, is there an oil that is generally considered the best?( Scoobysport suggest I should use Silkoline SYN5 - but thats what they sell, so id rather hear some other suggestions before I commit)
Cheers!
Alex

 

Alex

Why do you think we sell it?

 

Pete,

Do you use the same oil in the gearbox and the rear diff?

 

The box in my '91 4wd legacy was getting notchy after 110k miles . On advice from a mate who is the service manager at a dealership I changed the oil to Mobil synthetic gear oil (some of his customers who rally Imprezas use this). The box now feels like new .
Andrew ,
I think the rear diff uses heavy gear oil - check your handbook .

 

You can use SYN5 in the rear diff, but we prefer to use BOA90 LS.

The gearbox needs a 75w/90 API GL5 rated oil, the rear diff needs 80w/90 API GL5 although the manual says this does not have to be a multigrade (a fixed grade of between 80 and 90 is OK).

BOA90 LS and SYN5 have friction modifiers that improve the operation of limited slip diffs. You need 4.0 litres for the gearbox and 0.8 litres for the rear diff.

 

Sorry Pete,
Didnt want to offend! - I just wanted to know of some alternatives, as my experience of silkoline oils in competitive motocross is that although they are considered good, they are not necasseraly considered the best.

 

Thanks for the info Pete.

The manual is no help as the recommended lubricants are the same choice for gearbox and rear diff.