Automatic Transmission Fluids



Automatic transmission fluids (ATFs) are the most complex lubricants in the  
petroleum industry. Containing as many as 15 components, ATFs represent a  
careful balance of properties needed to meet the unique requirements of automatic  
transmissions. In terms of viscosity, they may be described as SAE 5W-20 grade  
oils with exceptionally good low temperature properties. They contain some of the  
same types of additives used in engine oils, together withfurther material to  
provide special frictional properties and improved oxidation resistance.
Because of their excellent low temperature fluidity and antiwear properties,
automatic transmission fluids often find use as hydraulic fluids in industrial equipment
and air compressors.
These fluids perform five basic functions:
  • Transmit hydrodynamic energy in the torque converter.
  • Transmit hydrostatic energy in hydraulic logic control circuits and servo-
  • Lubricate shaft bearings, thrust bearings, and gears.
  • Transmit sliding friction energy in bands and clutches.
  • Act as a heat transfer medium controlling automatic transmission
    operating temperatures.

Automatic transmission fluid specifications are in a state of flux and now there are
several types of fluid specified for North American automatic transmissions. The most
widely marketed fluid by far, is DEXRON-III / MERCON ATF , a friction modified
fluid, recommended for transmission top-up or refill, by most automobile manufacturers
for late model vehicles. However, the Ford Motor Company has recently announced, that
for 1997 models and beyond, it will require most of its transmissions to be serviced with
a new automatic transmission fluid...MERCON V. Although Chrysler allows DEXRON-III
ATF fluid to be used for transmission top-up, they prefer that Chrysler ATF+3 fluid be used,
where a complete change of transmission fluid is required. ATF Type F, a non friction-
modified fluid, is still required for 1979 and earlier Ford or other older import cars.