Automatic Transmission Fluid Oxidation

Automatic transmission fluid will provide 100,000 miles of service before oxidation occurs under normal operating temperatures of about 170F. 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:

175F 100,000 miles
195F 50,000 miles
212F 25,000 miles
235F 12,000 miles
255F 6,250 miles
275F 3,000 miles
295F 1,500 miles
315F 750 miles
335F 325 miles
355F 160 miles
375F 80 miles
390F 40 miles
415F Less than 30 minutes

This information clearly shows why transmission oil coolers and the various maintenance intervals are recommended for severe usage.

Above 300F, 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 very few minutes.

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