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EP90 , GL4 or GL5

Paul H

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I read in Practical Classics this month that EP90 GL5 wasnt suitable for our classics . Not ever hearing about GL4 or GL5 mild panic ensued as I checked the label on the tin of Castrol EP90 . There was no mention of either  so rang the help line and was advised that Castrol EP90 oil in their green tin was GL4 - Panic over 





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blimey this old nutshell continues to raise its head  more times than what oil for dashpots  ( sae20 or base 20/50)


there are some GL5 that are yellow metal tolerant but if unsure dont use it

 where as all GL4 is yellow metal tolerant ,


the adatives in most GL5 can disolve bronze/brass. copper metals if used in arduous working and very hot places  so things like baulk rings and thrust washers can suffer 


the diff has a harder life with oils than the gearbox and gets very hot  due to efficiency losses so planet thrusts may thin down.


i know from years of experience with truck reliability when one of our name changes involved a change of oil supplier and GL5 was introduced without prior concern and our older diff designs suffered thrust failures  in volume ...nightmare ,


dont take the chance unless you have a specific  GL5 oil spec thats compatible  with hot yellows .



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