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Automatic transmission fluids, motor oils, and multipurpose tractor oils are now widely used in hydrostatic transmissions. These fluids provide adequate service in most of today's relatively low pressure equipment, but future requirements will be more severe and better lubricants will be needed for tomorrow's larger, higher pressure equipment. An improved hydrostatic fluid has been developed which should help optimize performance of present and future hydrostatic transmissions. Results of a 100-hr, 5000 psi hydrostatic pump test were excellent. Analysis of the used oil and examination of the equipment indicated the fluid would have continued to perform satisfactorily much longer.

The performance of motor oils in engines run on unleaded fuels was evaluated using several makes of United States cars. These oils, SAE 10W-40 grades, were run in high mileage or turnpike service, as well as surburban service. The performance with unleaded fuels was not significantly different from that for leaded fuels in the areas of wear, sludge, varnish, or rust. Valve seat recession was detected in several of the cars, but had an effect on performance in only one case. Further testing using laboratory engines and a patrol fleet in pursuit service demonstrated the effect of lubricant composition on valve seat recession. In addition, it was found that engines preconditioned on leaded fuels afforded better protection against valve seat recession than new engines.

Hydrotreating is a relatively new process to manufacture high quality lube stocks through ring opening, isomerization, cracking, hydrogen transfer and other hydrogen reactions. Among the advantages of this process over solvent refining are greater crude flexibility, potentially high VI base stocks and increased flexibility in viscosity distribution. The hydrotreated base stocks are manufactured to be equivalent to solvent refined stocks and possess the added benefits of higher VI's, higher flash points and lighter colors. In addition, hydrotreated stocks show improved oxidation inhibitor response. This response is seen in engine oils and industrial lubes. In all other respects, hydrotreated stock performance with current additive systems is equivalent to solvent refined stocks in engine oils, automatic transmission fluids and gear oils.

Laboratory studies using bench, chemical and dynamometer tests were carried out to define some of the ways in which fluid degradation may occur and affect the serviceable life of an automatic transmission, as well as how components, individually or in combination, may accelerate or retard fluid degradation. Once these details were defined, the test results indicated two major conclusions. First, degradation products of an automatic transmission fluid (acids, sludges, varnish forming products, and so on) should be considered as new fluid components, since they may have more effect on transmission performance than the original components. And secondly, retention of desirable friction control properties must be a prime consideration in the design of a satisfactory automatic transmission fluid.

Rheological studies of an SAE 10W-40 motor oil were made over temperature and shear rate ranges typical of service. These include evaluations of both new and used oils. Determinations were made of the permanent viscosity changes during service, as well as the temporary non-Newtonian changes with shear. Data were taken at 60, 100, 210, and 250 F, which evaluated the oil from the initial first Newtonian to the second Newtonian regions. New oil viscosity measurements have little relation to the characteristics exhibited over most of the operating period between drains in an engine. Oils having similar initial viscosities can differ in service because of differences in formulation or service severity. It is evident that evaluation of the relatively “stable” used oil near or at the second Newtonian high shear rate region is the most informative. No convenient technique presently exists for such measurements on a large volume basis.