It’s commonly accepted that engine oil should be changed regularly, but less consideration is given to changing transmission fluid.

Although it doesn’t experience the same rigors as engine oil, in most cases it should still be changed regularly for best results. However, like engine oil, the change intervals can vary depending on use, conditions, equipment, and other factors.

ATF intervals are uncertain enough that whenever our sales team is out in the field, talking to our customers and with owners and technicians in repair shops, one question we are sure to hear is, “when should I really be changing a customer’s automatic transmission fluid?”

What is a “lifetime” interval?

When looking at various vehicle’s maintenance manuals you will notice different recommendations based on types of vehicles, driving conditions, miles driven, or in many cases advising that the fluid is “lifetime” and never needs to be changed.

It’s important to note that factory-fill “lifetime” automatic transmission fluids are made from higher quality base oil and additive packages, are more chemically stable, less reactive, and do not experience oxidation as easily as lower quality fluids made from lower quality base oils and additive packages. Therefore, higher quality transmission fluids, including factory fill, can last a long time in normal driving conditions, typically 100,000 miles or more. But now that vehicles are built to last 300,000 miles or more, the term “lifetime” is relative and could be shortened by not changing even higher quality fluids.

Also, the definition of “lifetime” varies from transmission manufacturer to transmission manufacturer. It is always important to consult the vehicle maintenance guide for proper service intervals depending on how the vehicle is driven.

Conditional Change Intervals

Let’s dig into the factors that contribute to determining the proper transmission change interval. For one example, the new Toyota Tundra owner’s manual states that when transmission fluid needs to be changed to consult the dealer, no specific frequency or mileage is mentioned. In other cases, your vehicle may be filled with “lifetime” fluid but still have more frequent service intervals depending on how you drive.

Just like engine oils, the definition of normal driving conditions are:

  • Carrying passengers or loads within the tire & loading information label
  • Driving on reasonable road surfaces

Where severe conditions include:

  • Mainly driven in heavy traffic in hot weather
  • Driven in hilly or mountainous terrain
  • Frequently towing a trailer
  • Used for high speed or competitive driving
  • Used for taxi, police, or delivery service

If driving conditions are half ‘severe’, half ‘normal’, fluid should be changed roughly twice as often. Therefore, a 45K-60K mile change interval is not unreasonable for even what might be specified as “lifetime” transmission fluid.

High Mileage Concerns

One other aspect to consider is if a vehicle operator waits to have the fluid serviced until 100,000 or more miles, they will find a number of service facilities refusing to do transmission fluid change. Service athigher mileage can lead to problems that may be blamed on the technician or service facility, when in fact delayed service is the culprit. For this reason, waiting until very high mileage, or until the fluid is compromised or symptoms are presented, might be too late. Your transmission might already be in decline and knowledgeable service facilities might not take the risk of changing the fluid to mitigate further damage.


Another concern to file under mileage: there are varying qualities of automatic transmission fluid and, like engine oil, if the least expensive is selected, the vehicle operator may want to increase the frequency that the fluid is changed.

In the end, follow the manufacturers recommendation for your specific type of driving, make sure that your servicing technician knows the type of driving you do, and follow the manufacturers requirement for the type of fluid that you should be using. Not all transmission fluids are equal in quality or compatibility.

Factory Quality

As an OE supplier, ENEOS not only provides factory fill to Asian OEMs, but we provide R&D for the fluids OEMs use. This ensures our lubricants are developed to the exact specifications (or greater) for each vehicle included in our coverage, and with the high quality and performance for which ENEOS is well known.

ENEOS transmission products include:

ENEOS ECO Series broad match fluid: ECO ATF PLUS for Asian OEMs, Dexron, Mercon  [3111-300]

ENEOS Import Series exact match fluid: Import ATF  for specific Asian OEMs