Motul GEARBOX 80W-90

Worth knowing

The figure of 21.7 mm²/s at 100 °C sets this oil apart from the other grade 90 oils in the Gear line: for GEAR 300, GEAR 300 LS and 90 PA the data sheets give 14.4 to 16.3 mm²/s. In the 2019 edition of SAE J306 such a value falls in the band of grade 110 (18.5 to 24.0 mm²/s), while grade 90 ends at 18.5. When describing the shear test, the data sheet cites the 1998 edition of the standard, in which grade 110 did not yet exist: the 2005 revision introduced it, splitting off the upper part of what was then grade 90.

With the mineral 90 PA it shares the same set of codes, API GL-4, GL-5 and compliance with MIL-L-2105D, and the same pour point of -24 °C. There the match ends: 90 PA is a single-grade SAE 90 with 14.5 mm²/s at 100 °C and is designed chiefly for limited-slip differentials, which GEARBOX is not meant for. Its data sheet declares compatibility with the “yellow” metals in gearbox construction; the article on GL-4 and GL-5 gear oil explains why brass and bronze synchronisers are sensitive to additives.