“In the coming years, even smaller transmissions will be responsible for handling as much if not even more torque, so fluids will have even more pressure put on them.” A Complex Formula “Transmission fluid has to be able to flow in extremely cold conditions to prevent slow shifting, which leads to a loss of fuel economy, and needs to provide excellent wear protection and frictional durability,” he continues. The fluid also needs to prevent varnish and sludge deposits that can clog narrow oil passages.

“In high temperatures, transmission fluid can’t get too thin or it won’t protect the vital gears and components of the transmission. “Transmission fluids need excellent thermal stability to stand up to both high and low temperature extremes,” says Ed Newman, advertising manager, AMSOIL. As we look forward, we can only see more complicated multi-speed and electronically controlled units requiring better fluids.” “Complex components such as automatic transmissions must have lubrication that cools, lubricates, resists oxidation from the high temperatures and allows clutch plates to smoothly engage and disengage thousands of times.

“Fluid design can play a major role in superior long-term function,” says Steve Rober, national sales manager, Schaeffer Specialized Lubricants. ATFs are even used as a hydraulic fluid in some power-assisted steering systems, as a lubricant in some 4WD transfer cases and even in some modern manual transmissions. They perform many functions including lubrication, heat dissipation, wear protection, shift quality and more, and are optimized for the special requirements of a transmission, such as valve operation, brake band friction and the torque converter, as well as gear lubrication. Automatic transmission fluids (ATF) rank among the most complex fluids used in vehicles.

Transmission fluid viscosity tests