Field and Laboratory Evaluations of Automatic Transmission Fluids D. Borden, A. Freedgood, and K. Rothert Enjay Chemical Laboratories THE RAPID INCREASE in the number of automobiles over the past several years (52 million cars in 1955 to 72 million cars in 1965), coupled with a shift toward large population clusters in urban areas (96 million people in urban areas in 1950 to 125 million in 1960, during which time the rural population remained virtually constant at 54 million), has resulted in a large percentage of the cars being involved in heavy stop-and-go driving conditions. The current trend in automotive design has been toward more accessories such as air conditioners, higher horsepower engines, and auto­ matic transmissions with smaller sump capacities. In terms of automatic transmission fluid (ATF) performance, these factors contribute to more severe operating conditions. Higher operating temperatures, caused by greater heat input and less efficient heat dissipation, decrease fluid life by in­ creasing oxidation of the fluid. (1, 2)* In light of this modern mode of operation a need exists to reevaluate the present techniques for measuring ATF per­ formance. Do they adequately predict fluid performance under today's severe operating conditions? A look at the present state of the art of evaluating auto­ matic transmission fluids may prove interesting. These fluids must perform many functions in today's sophisticated auto­ matic transmissions to insure overall customer satisfaction in day-to-day use. In order that the ATF will provide ac­ ceptable performance in consumer use, it must meet speci­ fic performance requirements in full-scale transmission tests, both engine and motor driven. Some other essential con­ siderations are such physical properties as good viscosity- temperature relationships, proper oiliness and lubricity char­ acteristics, elastomer compatability, and rust and foam prevention. These performance and physical tests provide an excellent means for offering a satisfactory automatic transmission fluid to the consumer and for deterring the com­ mercial introduction of substandard fluids. The application of these individual tests and groups of tests to the screening of automatic transmission fluids has been discussed in many publications. (3-5) The Enjay La­ boratories has used these techniques for many years to insure the performance of customer ATF formulations employing commercial additive packages and to screen new additive systems. However, two points have been of concern for some­ time: 1. These tests were designed to provide minimum per­ formance requirements for fluid approvals. As such they have been ample, but they did not provide a means of sep­ arating fluids of minimum quality from fluids of outstanding quality. * Numbers in parentheses designate References listed at end of paper. ABSTRACT - An outline of the field testing of automatic transmission fluids in two New York City taxicab fleets over a three-year period is presented. The field testing of six fluids in each fleet was found to be a suitable method for evaluating their relative quality. Some fluids performed satisfactorily for 11,000 miles while others were in service for over 90,000 miles. With extended fluid drain intervals, the major cause of transmission malfunction was fluid oxidation. No signifi­ cant relationship was found between the field test results and motor driven transmission and beaker bench oxidation tests. A fairly good correlation was established with engine driven cyclic transmission tests. The theory and modes of trans­ mission malfunction are also discussed. Downloaded from SAE International by University of British Columbia, Tuesday, September 25, 20182. No previous report had been published correlating these tests with actual field performance. Therefore, in 1962, the Enjay Laboratories undertook an investigation to determine: 1. The suitability of taxi fleet testi