The GL4/GL5 thing that seems to be getting more and more well known is based on out of date information. Back in the 1970s, when GL5 oils were first introduced, it was very quickly realised that the additives attacked yellow metals. That was no good to the oil manufacturer or user, so the additive pack was soon changed (by reputable oil companies) so that they use the same additives as in a GL4 oil, but in a higher concentration. That means that GL5 oils from reputable companies will not attack brass synchros. I donât know if that is the case with oils from companies that we donât deal with though.
There are certain GL5 oils that are better as diff oils as they are too slippery for synchros, but they are not attacking the brass.
I wouldgo for an ester based 75w-90 like the Fuchs Titan Race Synchro, Motul Gear 300, Millers CRX NT, Gulf Competition or Red Line MT90, although after speaking to Rob the other day, I was advised that the MT90 doesnât last well in the GTO boxes.
He is a transmission expert, working with 3000GT, evo, supra, GTR and more.
My question:
"Some say that class GL5 oil is not good for the syncros in 3S gearbox. But I got a 1999 VR4/TT, so my syncros are upgraded and can handle GL5?
We are having discussions on forums and your answers will be very much appreciated!"
His answer:
âMost synchro transmissions do not like GL5. This is why GL4 is what is typically recommended.
Itâs been our experience the gl5 does not work well in the Mitsubishi transmissions.â
I have now changed my gearbox oil anyway! Better safe then sorry
Regards
John
