Transmission Oil Aging – Passenger Car Manual Gearbox Applications (Part Two – Accelerated Testing and Field Performance)

An accelerated test methodology has been developed to reproduce long-term aging of Automotive Gearbox Lubricants. This test is essentially an anaerobic thermal stress test adapted from standard oxidation tests, except that nitrogen is bubbled through the oil instead of air or oxygen.

This test produces significant viscosity increase and heavy deposit formation with lubricants known to create similar problems in the field. However oils that remain stable in the field, that is do not increase in viscosity and do not lead to deposit formation also show no viscosity increase in this test. These fluids do show an increase in acid number and additive reactions/transformations that can be observed by ³¹P NMR.

Comparison with oxidation test results show that the nitrogen aging test gives closer results to known field performance.