Transmission fluid is petroleum based just like engine oil. Over time, both will deteriorate and their chemical properties will change – reducing the cooling and lubricating benefits. You wouldn’t drive 50,000 or even 100,000 miles without changing your engine oil and filter. So, why would you do the same with your transmission? Harrell & Beverly recommends that you have a Transmission Tune-Up Service completed once a year or every 15,000 miles. Doing so will help your transmission continue to run great and help you avoid costly repairs!