July 14, 2021 By Francis G. Pallarco

Servicing Automatic Transmission Fluid

Should I flush or should I change?

To Change or Flush?

Having the automatic transmission fluid checked/serviced is part of routine maintenance, just like having an engine oil change. Transmission gears require good quality fluid to deliver power from the engine to the drive wheels, shifting automatically to provide the best power and efficiency. But before deciding whether to flush or simply exchange the fluid, the first step is to understand the differences between the two.

Transmission Fluid Change

This procedure can only change around 50% of dirty fluid from the transmission oil pan and does not remove all harmful contaminants.  Normally consumes around 4-6 quarts.

Transmission Fluid Flush

This procedure gets rid of all the fluid from the pan, the oil cooler lines, as well as the torque converter and gets rid of most of the contaminants. Normally consumes around 10-12 quarts.

What’s The Difference?

The main difference is the amount of fluid being exchanged from the transmission as well as the method in which the fluid is being exchanged.  During a transmission service (drain and fill) around 30-40% of the fluid will be changed.  When performing a transmission flush (removal of oil trans oil pan) around 80-95% of the old fluid will be exchanged and the filter must be replaced.

Which One Should I Get?

There are different factors to consider before coming to a decision. First thing to consider is when the last time the fluid was changed.  If it’s a second hand car and there’s no way to find information, start by draining the fluid and have it checked by a technician before deciding what to do based on the fluid condition.  Also consider the actual mileage as the general rule of thumb would be to change the ATF every 50,000 kilometers, regardless of car manufacturers’ specifications or type of fluid used.

Fluid Types

Remember to use only the type of ATF specified/recommended by the vehicle’s car manufacturer. Different fluid specifications contain different additives and ingredients, which is why it’s important. The most common type of transmission fluid is the DEXRON and MERCON series. This is what most car manufacturers’ use today. There are also synthetic based ATF which provide different properties such as longer life and effectiveness in high heat.

Continuously Variable Transmission (CVT) Fluid

This type of automatic transmission seamlessly changes through a continuous range of effective gear ratios. This is different from conventional automatic transmissions, as it requires a CVT only specific fluid. Do not use ordinary ATF on your CVT to avoid transmission damage.

How often should the CVT fluid be changed?

This depends on how you drive your car. Normal average daily drivers wait until 60K to replace their CVT fluids, while others change at 30 or 40K. Always check the car owner’s manual and the condition of the fluid before changing. This will give a more accurate answer if you need to replace it.

Sealed CVT Transmissions

It is not uncommon to have sealed automatic transmissions these days whether CVT or conventional automatic as they come filed with longer lasting fluid. They don’t even have a dipstick in order to check the fluid level. If this is the case, have it checked/replaced based on the car manufacturers recommended service interval.

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