Understanding Automatic Transmission Fluid and its functionality in modern automatic vehicles

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The transmission fluid aids in proper valve operation, reduces brake band friction, lubricates the transmission gears, cools the transmission system, and helps the torque converter in proper functioning.

No matter whether your application has an automatic transmission system or a manual transmission system, the transmission fluid always plays a vital role in maintaining the functionality.

Although most modern vehicles come with an automatic transmission system, a manual transmission system is still prevalent in many vehicles and mechanical machinery.

But for now, I will be covering the Automatic Transmission Fluid (ATF) only, which is a bit different than the manual transmission fluid.

Automatic Transmission Fluid

Types of transmission

An engine transmission system is of six different types. These are-

  • AT or Stepped  Automatic Transmission (uses a  planetary gear set and torque converter)
  • CVT or Continuously Variable Transmission (uses variator pulleys with unlimited gear ratios)
  • DCT or Dual Clutch Transmission (uses manual gearbox architecture and dual clutches)
  • AMT or Automated Manual Transmission (use servos to engage clutch and shift gears automatically)
  • EVT or Electrical Variable Transmission (stepped automatic transmission with an electric motor)
  • MT or Manual Transmission

Except for the Dual Clutch Transmission and Manual Transmission, all the rest falls in the category of Automatic transmission system.

In order to understand how each of the transmission systems works in motor vehicles, consider checking this extract written on Automatic transmission Fluids.

What is automatic transmission fluid?

ATF  or Automatic Transmission Fluid is a type of transmission oil that is used in vehicles with an automatic transmission system or self-shifting gear mechanisms.

Although ATF comes for automatic transmission systems, many modern vehicles with a manual o hydraulic transmission system are also using ATF to lubricate the transmission.

Types of transmission fluid

Transmission fluids are of five different types. These are-

  • Type A and Type F
  • Dexron and Mercon
  • HFM or Highly Friction Modified Fluids 
  • Synthetic ATF 
  • Fully Synthetic CVT Transmission Fluid

Type A and Type F

Type A and Type F transmission oil was an integral part of the old vehicles found during the 1970s.

Type A and Type F lubricant fluids are almost extinct in modern vehicles.

Dexron and Mercon

Both Dexron and Mercon transmission fluids come with a friction modifier.

Therefore, these transmission fluids are good for reducing temperature and friction in the transmission system.

Highly Friction modified(HFM) Fluids

HFM is a type of synthetic oil that enhances the performance capability of the engine. HFM fluids are usually used in high-performing engines.

Synthetic ATF

The characteristics of synthetic ATF and the characteristics of  Dexron and Mercon are almost the same.

Fully synthetic CVT transmission fluid

CVT transmission fluid is a bit different than ATF. CVT transmission fluid is good for reducing higher friction and ensures smooth engine operation. At the same time, CVT transmission fluid ensures protection against thrust.

By preventing oil viscosity change at a lower temperature, the CVT transmission fluid ensures longevity.

CVT transmission fluid also brings protection against oxidation.

Another benefit of using the CVT fluid is that it prevents the machinery from wearing. Therefore, the parts of the engine and the transmission system stay healthy for a long time.

Understanding automatic transmission fluid

In order to ensure perfect operation for all the parts of the transmission assemblies, it is necessary to have a better lubricator that will keep the engine environment cool and workable.

For most vehicles with an automatic transmission system, we call that lubricator ‘ATF’ or Automatic transmission Fluid.

Lubricating oils for modern automatic transmissions of motor vehicles is a great conference paper that you may check to understand the operation and functionality of ATF.

Function and traits of ATF

Here are some of the primary traits and functionality of ATF-

  • Lubrication
  • Anti-wear 
  • Ensuring oxidation and thermal ability
  • Temperature control
  • Friction management
  • Oil viscosity control both in high and low temperature

Why the quality of automatic transmission fluid may drop?

Not using the specific ATF

It is always recommended to use the manufacturer-specified ATF to get maximum functionality and stability out of your vehicle.

Using an unauthorized or after-market transmission fluid may make the transmission system vulnerable.

Mixing fluids

Mixing one type of transmission fluid with another and pouring the whole mixture into the fluid chamber is another reason why the quality and performance of the transmission fluid may drop.

Flush the whole fluid out if you do not know which brand you should use.

Ensure that you are using the manufacturer's proposed right graded lubricant for the system.

Not changing oil fluid for a long time

It is recommended that one should change the lubricant oil twice between every 40,000 and 80,000 miles.

Check the manufacturer specification before you inspect or change the lubricant.

Sometimes it is better to flush transmission fluid before the manufacturer’s specified timeline

Most modern automatic vehicles specify to change the lubricants every 100,000 miles. Some high-end Ford models even recommend changing transmission fluid every 150,000 miles.

Even if the oil grade looks better according to the manufacturer's manual, it might be a better decision to flush the lubricant oil out before the manufacturer's specified timeline.

If water or coolant mixes with the fluid

When flushing or changing the transmission fluid, any intervention of water and coolant to the fluid can also deteriorate the overall quality of the fluid. 

At the same time, a very low temperature might also reduce the viscosity of the oil, which can ultimately reduce the fluid performance.

Burned transmission fluid

Burned transmission fluid is another reason why the quality of the fluid may drop.

At the same time, burned transmission reason can be the initial reason behind transmission system failure.

Is fluid change necessary for Automatic vehicles?

Yes, it is necessary to change the transmission fluid even for automatic vehicles.

Many automatic car owners do not even know that there is a fluid chamber inside their vehicle.

When you are driving usual, you may get away without changing the transmission fluid present in your vehicle.

But driving heavily or going off the road may burn the transmission fluid inside, which can create serious transmission errors in the long run.

Therefore, inspect your vehicle’s transmission fluid after every 40,000 to 60,000 miles and flush if necessary.

How often should you replace transmission fluid?

It is recommended to flush the transmission fluid of any automatic vehicle after every 50,000 miles.

But this can be misleading depending on the brand of car you have and how roughly you are using your vehicle.

High-end luxury vehicles usually demand fluid change after every 60,000 miles.

An average mid-range automatic car will demand fluid change somewhere between 35,000 miles and 40,000 miles.

Always follow the manufacturer’s suggestion before you go flushing the transmission fluid of your car.

Here are usual fluid change recommendations for different car brands-


Fluid change timeline

General Motor

45,000 miles


60,000 miles


50,000 miles


150,000 miles





How to inspect transmission fluid?

To find out any problem with the transmission fluid,  the color of the fluid is the strongest indicator.

By inspecting the color of the lubricant, a professional mechanic can easily determine whether the fluid is worth changing or not.

Therefore, it is necessary to have better knowledge and understanding regarding the transmission fluid to detect any issues with the lubricants.

Drain or flush?

Well, you need to decide whether to drain or flush the transmission fluid by following the manufacturer’s specifications.

Depending on the oil type, every vehicle's manual tends to specify whether to flush or drain the fluid.

Ensure that you are giving the manual a better check.

How much does it cost to flush transmission fluid?

Flushing or draining the transmission fluid out of the chamber should not cost more than $100.

Anyway, high-end luxury cars may require around  $200 to $300 for draining or flushing the transmission fluid.

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