DML FAQ : Transmission and Gears : How does temperature affect transmission fluid life?
Automatic transmission fluid will provide 100,000 miles of service before oxidation occurs under normal operating temperatures of about 170°F. Above normal operating temperatures, the oxidation rate doubles (useful life of fluid is cut in half) with each 20° increase in temperature.
The approximate life expectancy at various temperatures is as follows:
|415°F||Less than 30 minutes|
This information clearly shows why transmission oil coolers and the various maintenance intervals are recommended for severe usage.
Above 300°F, the metals inside the transmission will warp and distort in varying degrees depending on the severity of overheat. Because this damage occurs and fluid life is so seriously impaired, rocking out of snow, mud or sand should never exceed a few minutes.
Synthetic fluids are better but can still be compromised under extreme conditions.