Actual meaning of lifetime transmission fluid
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Transmission fluid is used to lubricate the internals of the transmission. It is also used to cool the transmission. Torque converters use transmission oil to transfer power from powertrain to the transmission.
Lifetime means duration of life. Hence, a lifetime transmission fluid ordinarily means fluid that lasts the lifetime of the transmission.
Technically, there is more to the meaning of lifetime transmission fluid. When people say they last the lifetime of the transmission, they may be right or not right. Theoretically yes, but practically maybe no.
There have been many other definitions. Some attribute it to warranty period. Others attribute it to 100 miles, 120 miles or 150 miles of vehicle usage.
From our study and experience, the meaning has less to do with period of time but more of how the transmission works. We recommend that you read this concerning adaptive transmissions to understand the explanation that will follow below.
Technology that makes lifetime transmission oils usable
Since the introduction of adaptive transmissions, manufacturers are able to minimize the number of required maintenance especially oil changes. As the transmission and the vehicle are being used, the oil degrades and components wear out. Adaptive transmissions are able to adjust shift pressures and shift timings in accordance with the conditions of fluid and other components of the transmission. As a result, the fluid and transmission can be used for a long period of time without requiring frequent maintenance.
Is oil change necessary when using lifetime transmission fluid?
These fluids are top quality fluids and they are built to withstand a lot of heat and stress. However, wear and tear of transmission components can only be minimized and slowed down, it cannot be eliminated completely. Hence, the lifetime fluid never remain fresh therefore fluid change is advisable even before the adaptive transmission gets to a point where it has fully utilzed the fluid and has gotten to a threshold point where it can no longer continue to adjust shift pressure and timing. When the transmission is left without oil change and it gets to this point, usually there is already serious wear in the internal components of the transmission and introduction of a new fluid could spell trouble especially if transmission reset and relearn procedure is not carried out either manual or automatically.