ATF Automatic Transmission Fluids

Automatic transmission fluids

Automatic transmissions are now more complex than ever. In fact, the automatic transmission is perhaps the most complicated mechanical component in a car. The automatic transmission combines electrical & mechanical systems, hydraulics and computer processors to shift smoothly through the gears and transfer engine power to the drive wheels. They place huge demands on automatic transmission fluids (also known as ATF oil).   

Castrol ATF fluid product range

Castrol offers a wide range of ATF fluids designed to protect critical transmission components and help prolong component life. These include our premium Castrol TRANSMAX ATF  fluids formulated with Smooth Drive Technology™ to provide smoother gear changes for longer and deliver a more relaxing drive.

Automatic transmission fluids FAQs

Q: Why can I find EP on the label of ATF oils?

A: EP stands for extreme pressure. EP is an additive designed to stop metal-to-metal contact taking place between transmission components.

Q: Will synthetic gear oils and mineral gear oils mix together?

A: Yes, but always check the specifications in your manufacturer’s handbook to make sure that you are using an oil of the right specification.

Q: Are filled for life gear oils a good idea?

A: In theory these are fine but it’s a good idea to change ATF fluids periodically to flush out wear debris. You should consult your manufacturer’s handbook for recommendations.

What is automatic transmission?

An automatic transmission is a multi-speed transmission which transfers power from the engine to the driveshaft without the driver having to change gears. 

Types of automatic transmission fluids

Over the years there have been different types of ATF oil or trans fluid developed by different manufacturers and the introduction of new technologies.

1. Type F – This is now a rarity and can only be found in the gearbox of classic cars.
2. Dexron III/Mercon - This is one of the most common automatic transmission fluids on the market and is the right ATF fluid for most GM and Ford cars as well as many Japanese and European brands. 
3. HFM-Style fluids – These ATF oils have been specially developed for all Audi, VW, Porsche, Volvo, Toyota, Lexus and Saab models (amongst others) fitted with an Aisin Warner automatic transmission.

Synthetic fluids offer improved resistance to heat, cold, oxidation and sheer and are the reason why many manufacturers have eliminated the transmission dipstick. Their improved characteristics mean that there is less reason to access a vehicle’s transmission and its operation between services. 

Automatic transmission fluid vs manual transmission fluid

Automatic transmission fluids are distinctly different from fluids made for manual transmissions. The properties of a high performing ATF fluid are:

1. Heat resistance and thermal stability to help prevent deposit and sludge from forming due to high temperatures
2. Frictional characteristics to enable smooth gear changes by supplying the correct friction to the transmission clutches and bands
3. Extreme pressure/load carrying performance to ensure anti-wear and gear durability
4. Viscosity stability or proper fluid thickness over a wide temperature range
5. Low temperature flow to ensure effective operation of hydraulics and electronics controls at low temperature

Key performance and protection requirements for manual transmissions: 

1. Synchronizer compatibility, durability and shift quality. 
2. The transmission synchronizer must engage smoothly for proper shift performance.
3. Anti-wear and load carrying components in the transmission fluid must ensure long synchronizer life and gear protection. 

Always consult your car’s handbook to make sure you find the correct fluid for your transmission.