801363 The Prediction of ATF Service Life from Laboratory Oxidation Test Data COPYRIGHT. /*?%& SOCIETY OF AUTOMOTIVE ENGINEERS, INC. P. A, Willermet, L. R. Mahoney, S. K. Kandah, and A. W. Sever Research Staff Ford Motor Co. Dearborn, MI THE thermooxidative stability of automatic transmis­ sion fluid is a critical factor in achieving long-term transmission durability. Although many ATF formula­ tions are currently available which give acceptable performance, changes in composition can be expected to take place due to factors such as base stock availability and the introduction of new fluid formula­ tions by suppliers. In order to facilitate ATF development and to help select the best fluid for a particular application, it would be desirable to have available an oxidation test procedure which has dem­ onstrated correlation with service and which is at the same time inexpensive and convenient. A laboratory beaker oxidation test could fulfill the cost and convenience requirements. In order to determine if such a test can also be correlated with ATF degradation in service, we have carried out a systematic comparison of laboratory oxidation test data and data obtained for the same ATFs in vehicle service. We have previously reported the results of a study of antioxidant depletion which showed that the early stages of ATF oxidation in vehicles could* be ■modelled by the Ford Aluminum Beaker Oxidation Test -K- (ABOT) procedure (1). This report deals with the later stages of oxidation, up to and including oxidation related to transmission failure. ^Numbers an parentheses designate References at end of paper. EXPERIMENTAL TEST PROCEDURE - The apparatus and test proce­ dures used in this study are described in a previous paper (1) and in Ford Laboratory Test Method B3 10-*. Briefly, the fluid under test is oxidized in an aluminum beaker of @425 mL capacity. A steel gear pump in the .beaker, driven at 1000 rpm, circulates the fluid and provides for intimate mixing with air flowing into the system at 5cc/min. Lead, steel and copper parts are included to represent materials in transmissions. Aliquot samples are withdrawn periodically and ana­ lyzed for pentane insolubles, IR absorbance, total acid number and viscosity. ATF PROPERTIES - The same letter designations are used in this report and in (1). Description of the various fluids are given in Table 1. FORMATION OF PENTANE INSOLUBLES - Data for the formation of pentane insolubles for several fluids in the ABOT and in service are presented in Figs. 1-3. These data show that the details of the pentane insolubles formation yaried from fluid to fluid. The value of one percent pentane insolubles was chosen as a test failure criterion because it is readily measure- able value and is usually reached soon after the onset of detectable pentane insolubles formation. Experi­ mental values for the times required to generate 1% pentane insolubles are summarized in Table 2. The Ford Aluminum Beaker Oxidation Test was developed as an inexpensive and convenient test procedure for evaluating the thermooxidative stability of ATFs. This paper presents the results of a systematic study of ATF oxidation in this test and in ■ ABSTRACT - vehicle service. The results show that ATF service life in vehicles could be predicted by extrapolating laboratory oxidation test data using temperature co­ efficients for oxidative processes. SAE/SP80/473/$02.50 Copyright © 1980 Society of Automotive Engineers, inc. Downloaded from SAE International by University of Wisconsin - Madison , Monday, September 10, 20182 Table I - Analysis of Fresh Fluids Elemental Analyses, PPM Fiuid Type JL Zn B Na Ca MS TAN TBf> A M2C -33F 310 320 --360 -1.2 1.6 B M2C -33G 530 460 - 330 370 - 0.9 C M2C -33G 360 310 190 --- 0.7 a M2C -138C3 230 200 40 - 40 60 1.0 E n " 570 6*0 -- 5*0 - 0.8 2.5 F " « 390 110 170 --- 0.9 1.9 G " " 200 ISO 30 -- 50 0,8 2.1 H M2C -33F 3