Browse Publications Technical Papers 2003-01-1985

Extended-Drain ATF Field Testing in City Transit Buses 2003-01-1985

City transit buses are a severe environment for an automatic transmission fluid. The fluid must endure very high operating temperatures because of the use of brake retarders, frequent stop-and-go driving, and numerous shifts. There is an increasing trend toward the use of extended-drain, synthetic-based ATFs for such severe service applications. This paper documents a field trial with both synthetic and petroleum-based ATFs at a large municipal bus fleet in Southern California. Three different commercial ATFs, made with either API Group 2, 3, or 4 base oils, respectively, were compared after roughly 80,000 km. and one year of operation. Because of different additive packages in each fluid, not all of the results can be explained by base oil effects alone. However, the base oil is certainly a dominant contributor to the finished fluid performance. The following four variables were monitored by used oil analysis: iron wear, copper wear, viscosity change, and acid number change. The two synthetic-based ATFs showed directionally better performance in copper wear, viscosity change, and acid number increase compared to the Group 2-based ATF. There was no significant difference in ferrous wear protection between the three ATFs. The Group 2-based ATF is capable of providing at least double the OEM-recommended drain interval. The Group 3- and the Group 4-based ATFs can achieve 80,000 km drain intervals, which is four times the interval recommended by the OEM.


Subscribers can view annotate, and download all of SAE's content. Learn More »


Members save up to 16% off list price.
Login to see discount.
Special Offer: Download multiple Technical Papers each year? TechSelect is a cost-effective subscription option to select and download 12-100 full-text Technical Papers per year. Find more information here.
We also recommend:

Long-Term, Heavy-Duty Field Test Comparison of Four GL-5 Gear Lubricants


View Details


Development of a test method to evaluate the life of gear oils for heavy-duty vehicles


View Details


Formulating Automatic Transmission Fluids with Improved Low Temperature Fluidity


View Details