When to Change Automatic Transmission Fluid: Performance Requirements and Mistakes

Transmission is the vital part for vehicle common operation, and owing to the special working condition, the transmission is easily to over heat and wear. Therefore, transmission fluid becomes the first choice of solve thus problem.

 

The classification of transmission.

According to the working principle, transmission can be divided into hydraulic automatic transmission (AT), dual-cluth transmission (DCT), automated manual transmission (AMT), and continuously variable transmission (CVT).

 

The requirement demands for transmission fluids.

In order to component wear and prolong the transmission service life, it's often add transmission fluids into the transmission. The transmission fluids have the functions of lubricity, seismic resistance, cooling and anti-oxidation.

 

Automatic Transmission Fluid (ATF) is the most functionally complex type of automotive lubricant. Typical ATFs meeting DEXRON III and MERCON V specifications consist of high-quality base oil blended with 10% to 25% additives. Viscosity index improvers account for one-third to two-thirds of this additive content, serving to increase high-temperature viscosity and improve low-temperature fluidity; the remaining additives-such as dispersants (to keep carbonaceous oxidation products in suspension), antioxidants, and anti-wear agents-are adjusted flexibly according to the specific formulation.

 

Viscosity index modifiers-improve temperature viscosity performance and shear stability

The working temperature range has a large span, form the normal temperature to over 200℃, the base oil viscosity has a large change with the temperature changes.

 

Viscosity index modifiers (the common used in PMA ) stretching and thickening of molecular chains at high temperatures, and their contraction and pour-point-lowering effect at low temperatures.

It should be noted that the polymer with a high molecular quality (10万～20万)has a quicker viscosity loss under mechanical shear. The low molecular weight quality (3万～6万) not only has a small permanent shear loss, but also a lower temporary viscosity loss under high shear.

Synthetic base oils (such as PAO or esters) possess inherently high viscosity indices, allowing for the elimination or reduction of viscosity index improvers. This prevents viscosity loss due to shear and ensures long-lasting lubrication.

 

Anti-oxidation-inhibiting oxidation and deposit formation

The high-speed churning and friction of internal transmission gears generate significant heat, causing the fluid to oxidize and thicken while forming corrosive acidic substances and sludge. Consequently, antioxidants are required to inhibit the formation of these acidic substances and sludge.

The high-speed churning and friction of internal transmission gears generate significant heat, causing the fluid to oxidize and thicken while forming corrosive acidic substances and sludge. Consequently, antioxidants are required to inhibit the formation of these acidic substances and sludge.

 

Extreme pressure & anti-wear additive-protect the gear surface under boundary

Under high torque conditions, when the oil film in the tooth contact zone breaks, the extreme-pressure & anti-wear additive containing sulfur, phosphorous, or chlorine react with metal and form a protective film with low shear strength, such as iron sulfides and phosphates to prevent scuffing and welding.

 

However, the polarity of the base oil will influence the additives compete to adsorb, ester base oils have a higher polarity than mineral oils and PAO base oil that can disrupt the balance among anti-wear additive, anti-rust additive, and friction modifiers.

In addition, the anti-wear performance is not rely on lubricant additives, but also it's related to the oil's high temperature high shear (HTHS) viscosity. The higher HTHS viscosity can help to maintain the hydrodynamic oil film, an reduce the wear on components such as planetary gear pins.

 

The common mistakes in changing transmission fluids.

Mistake 1: it's no need to change transmission fluids

In fact: the transmission oil don't change will oxidize and thickening, influencing lubricity and heat dissipation. Although the transmission temperature is lower than engine, it has large temperature change, and the oil will oxidize quickly, resulting in the heat dissipation and lubricant performance decrease and influence the normal operation of transmission.

 

Mistake 2: different transmission can mixed use

Fact: Mixing transmission fluids of different brands or specifications may result in:

Additive incompatibility, leading to the performance loss or the sediment formation;

Inadequate lubrication or power transmission, causing jerky gear shifts and a lack of power;

Influencing the service life of the transmission.

 

Recommended transmission change period:

Generally, the transmission fluid change interval for cars is approximately 60,000 to 80,000 kilometers;

Please refer to the specific manufacturer's maintenance manual, as intervals may vary depending on the vehicle model and transmission type.

 

Chorus is a professional lubricant additives supplier, we can provide you with various kinds of transmission oil additive, include ATF, DCT, CVT, and also gear oil additive packages.

 

Also, we can offer you other excellent performance lubricant additives, such as viscosity index improvers, anti-oxidation additives, and extreme pressure additives.

If you need automatic transmission fluid, please contact us.