# Gear box oil ratings question.



## adonisito (Nov 6, 2009)

The book for my 1999 2.5d Boxer says 75w 80 manual transmission fluid, I have bought Castrol Syntrans 75w 90 fluid, as I couldn't find the former. Does anyone know if its OK to put it in ? The Castrol site suggests Syntrax and I'm getting confused !

Thanks as usual.


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## listerdiesel (Aug 3, 2012)

That will be fine.

Peter


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## DavyS (Jan 10, 2009)

The 90 bit is really only needed for hot climates, the 75 bit for cold climates below zero; so in UK an 80 would be sufficient. Oil that is too thick causes slow or difficult gearchanges when cold, so dont go below 75.

GL5 gives better protection at high pressure but according to Wikipedia, GL5 is low friction and some synchros wont work with it and are better off with GL4. 
GL5 erodes brass synchro rings faster than GL4. If you are not doing a lot of milage or thrashing the gearbox at heavy load then using GL4 might mean the synchro rings last longer.


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