Una persona che lavorava nel campo me l'aveva accennato, ed ora ho trovato qualcosa di interessante sulla materia, e cioe' un documento della penzzoil.
Sembra che l'additivazione EP (estreme pressioni), in caso ad esempio di sincronizzatori in bronzo o boccole in ottone, sia molto molto deleteria.
In sostanza, ad esempio, se nel libretto la casa richiede nel cambio un olio con specifiche GL-3 (non additivato EP), mettendo un GL-5, in teoria piu' performante, si rischia di far danni.
http://www.pzlqs.com/Tech/Bulletin//DomesticMarketing/General/pdf/g14c.pdf2. What happens if API GL-5 gear oil is used in an API GL-4 gear oil application?
API GL-4 and API GL-5 products typically use the same extreme pressure (EP) additive system, with
the API GL-5 having about twice the concentration of a API GL-4. In service, these additives become
active under extreme load and temperature when the protective oil film can be squeezed away. EP
additives work by forming wear-resistant compounds with the metal of the gear tooth surface. As the
gears mesh, these compounds shield the gear teeth from direct metal-to-metal contact that would cause
wear and damage to the gears. If too little of the active additive is present, proper protection would be
compromised. Too much of this additive could cause excessive chemical corrosion of the gear surface.
If an API GL-5 gear oil is used in a application where API GL-4 gear oil is called for, chemical
corrosion of “yellow metal” components may occur, such as bronze synchronizers, brass bushings, etc.This may lead to shifting difficulties or shortened equipment life.
