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Design changes in automatic transmissions have resulted in new requirements for automatic transmission fluids. Electronic controls, for instance, perform best with fluids having better low-temperature properties. Achievement of the target low-temperature properties can be accomplished in different ways. The advantages and disadvantages of each approach are discussed with respect to total fluid performance. Fluid performance properties examined include viscometrics, shear stability, antiwear and stability toward thermal stress and oxidation.

Automatic transmission fluids (ATFs) are required to possess a high level of antiwear (AW) characteristics in order to function properly in the multitude of applications where such products are used. Generally DEXRON®-II* or MERCON®** fluids have given good AW performance in the field. However, ATFs of different chemistries might exhibit different levels of AW performance. Experimental work with ATFs of different chemistries has shown wide differences in AW levels. Thus, tests were carried out with the GM power steering pump test, the vickers pump (MERCON® procedure) test, the FZG Low-Speed Wear test, the CRC L-20 gear test and several industrial pump tests. The results show that significant amounts of metals in the product detract from some aspects of the AW properties, and an ashless formulation can be the best choice.