Just like your engine oil, transmission fluid breaks down and has a service life depending on the vehicle and what its job duties are. Service intervals can be found in your owner's manual but we have found these intervals to not be adequate with today’s driving conditions. We suggest every 30,000 miles on vehicles and if extreme towing is all the vehicle does it is always good to shoot for 15,000 to 20,000 miles. Maintaining and servicing your vehicle will prolong its life immensely so you don’t have the costly expense of replacing a transmission at the most inopportune time. Knowing when maintenance is due is also a great way to budget your finances.