There are many fluids that run throughout your vehicle, but one of the most important to keep track of is the transmission fluid. Whether or not you should change it is not a matter of debate: Yes, you should. But how often this service should be performed varies by manufacturer and vehicle, and it’s open to debate.
The manufacturer’s maintenance schedule for many automatic transmissions doesn’t call for fresh fluid until 100,000 miles or, with some Ford transmissions, even 150,000 miles. A lot of mechanics say that is too long and that it should be done at least every 50,000 miles. Manual transmissions require more conventional gear oil rather than ATF and tend to be on a different maintenance schedule, so it’s best to consult the service intervals in the owner’s manual.